basic hydraulics - Oakland High School

Transcription

BASIC
HYDRAULICS
LEARNING
ACTIVITY
PACKET
HYDRAULIC POWER SYSTEMS
TM
4
BB831-XA01XEN
LEARNING ACTIVITY PACKET 1
HYDRAULIC POWER SYSTEMS
INTRODUCTION
Hydraulic power technology is used to power machines in almost every
manufacturing plant in the world. It has many unique features that have caused its use to
continue to grow rapidly.
This module will explore the basic skills in hydraulics. It will discuss how to
connect and operate basic components and systems, read circuit diagrams, monitor
system operation, and design circuits.
When performing skills, the Amatrol 850 series hydraulic trainer will be used. This
trainer is designed with real world industrial components that will allow the operator to
set up actual circuits and test their operation.
This first hydraulic LAP will explain how to start up and operate a hydraulic power
supply and then connect a basic circuit.
ITEMS NEEDED
Amatrol Supplied:
1 85-BH Basic Hydraulic Training System
1 85-HPS Hydraulic Power Unit
School Supplied
Shop Towels or Rags
FIRST EDITION, LAP 1, REV. C
Amatrol, AMNET, CIMSOFT, MCL, MINI-CIM, IST, ITC, VEST, and Technovate are trademarks or registered trademarks of Amatrol,
Inc. All other brand and product names are trademarks or registered trademarks of their respective companies.
Copyright © 2011, 2009, 1986 by AMATROL, INC.
All rights Reserved. No part of this publication may be reproduced, translated, or transmitted in any form or by any means, electronic,
optical, mechanical, or magnetic, including but not limited to photographing, photocopying, recording or any information storage and
retrieval system, without written permission of the copyright owner.
Amatrol,Inc., 2400 Centennial Blvd., Jeffersonville, IN 47130 USA, Ph 812-288-8285, FAX 812-283-1584 www.amatrol.com
BB831-XA01XEN HYDRAULIC POWER SYSTEMS
Copyright © 2011 Amatrol, Inc.
2
TABLE OF CONTENTS
SEGMENT
1 INTRODUCTION TO HYDRAULICS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
OBJECTIVE 1 Define hydraulics and give an application
OBJECTIVE 2 Describe the functions of five basic components of a hydraulic system
Activity 1 Hydraulic Trainer Component Identification
OBJECTIVE 3 Define hydraulic pressure and give its units of measurement
SKILL 1 Read a hydraulic pressure gauge
SEGMENT
2 POWER UNIT OPERATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
OBJECTIVE 4 Describe the operation of a hydraulic power unit
Activity 2 Identification of 850 power unit components
SKILL 2 Read the liquid level and temperature in the reservoir
SKILL 3 Operate a hydraulic power unit
SEGMENT
3 CIRCUIT CONNECTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
OBJECTIVE
OBJECTIVE
SKILL
OBJECTIVE
SKILL
OBJECTIVE
5
6
4
7
5
8
SEGMENT
4 BASIC CYLINDER CIRCUITS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
Describe the function of a hydraulic schematic
Describe the function of a hydraulic quick-connect fitting and give its schematic symbol
Connect and disconnect a hydraulic hose that uses quick-connect fittings
Describe the function of a tee and give its schematic symbol
Use a tee to connect two circuit branches together
Describe the operation of a pressure gauge and give its schematic symbol
OBJECTIVE 9 Describe the function of a hydraulic cylinder and give an application
OBJECTIVE 10 Describe the operation of a double-acting hydraulic cylinder and give its schematic symbol
Activity 3 Basic operation of a double-acting cylinder
OBJECTIVE 11 Describe the function of a 3-position, 4-way DCV and give an application
OBJECTIVE 12 Describe the operation of a 3-position, 4-way DCV and give its schematic symbol
Activity 4 Flow paths of a 3-position, 4-way DCV
SKILL 6 Connect and operate a double-acting hydraulic cylinder using a 3-position, manually-operated
DCV
SKILL 7 Design a dual cylinder hydraulic circuit
3
SEGMENT 1
INTRODUCTION TO HYDRAULICS
OBJECTIVE 1
DEFINE HYDRAULICS AND GIVE AN APPLICATION
All machines require some type of power source and a way of
transmitting it to the point of operation. The three methods of
transmitting power are mechanical, electrical, and fluid.
Fluid power deals with the transmission and control of energy by
means of a pressurized fluid. Although it is common to think of a fluid as
simply a liquid, a fluid is actually considered to be either a gas or a
liquid. Hence, there are two primary branches of fluid power:
• Hydraulics - Which uses a liquid, usually oil
• Pneumatics - Which uses a gas, usually air
An example of how hydraulics can be used for energy transmission
is shown in figure 1.
ELECTRIC
MOTOR
CONVEYOR
HYDRAULIC
MOTOR
PUMP
RESERVOIR
OIL
Figure 1. Using Hydraulics to Drive a Conveyor
4
In this example, hydraulic power runs a conveyor. To do this, an
electric motor rotates a hydraulic pump shaft causing the hydraulic pump
to pump oil from a tank or reservoir through a pipe to a hydraulic motor.
The pumped oil causes the hydraulic motor shaft to rotate, turning the
conveyor drive. The oil leaving the motor returns to the reservoir to be
used again.
Hydraulics is an important part of modern industry. In almost any
industrial career hydraulic-powered machinery will probably be worked
with or around. Some of the applications that use hydraulics include:
Manufacturing
• Some industrial robots are powered by hydraulics.
• Many industrial machines use hydraulics for their power source.
• Plastic injection molding machines use hydraulics to close the
mold.
• Lifting devices, including fork trucks, use hydraulic power.
Transportation
• Commercial airplanes use hydraulics to control the moving
surfaces and for lowering and raising the landing gear.
• The shock absorbers used on cars and trucks use hydraulics.
• Brake systems for cars and trucks are powered by hydraulics.
Construction
• Digging equipment such as backhoes use hydraulics.
• Bulldozers, graders, and dump trucks use hydraulics.
5
Figure 2. Application of Hydraulics in Plastics
Many applications use hydraulic systems because they can provide
very high forces and can smoothly and accurately control the motion of
the machine. Hydraulic systems also have the advantage of being able to
operate under water and in other harsh environments.
However, hydraulics isn’t the solution for every application. For
example, because hydraulic systems can leak oil, they don’t work well in
clean room applications.
6
OBJECTIVE 2
DESCRIBE THE FUNCTIONS OF FIVE BASIC COMPONENTS
OF A HYDRAULIC SYSTEM
All hydraulic systems consist of five basic components:
• Power Input Device - This is the pump that provides hydraulic
power to the system. The pump draws oil from the reservoir and
pumps it into the supply line.
• Control Devices - Valves control direction, pressure, and flow rate
of the pressurized oil in the hydraulic system.
• Power Output Device - This is where the hydraulic power is
converted back to mechanical power. These output devices are
called actuators. Two types of actuators are motors and
cylinders. The motor creates rotary motion as the oil flows
through it. The cylinder creates straight line motion when oil
flows into it.
• Conductors - To transmit the liquid, conductors (pipes, tubing, or
hoses) are needed. There are two main lines in a hydraulic
system: the supply line and the return line. The supply line
provides flow to the actuators. The return line allows oil leaving
the actuators to return to the reservoir.
• Liquid - This is our power conducting medium. Typically, this is
oil but other liquids are sometimes used.
FLOW
CONTROL
VALVES
OIL
FLOW
ELECTRIC
MOTOR
LINEAR
MOTION
OF ROD
SUPPLY
LINE
RELIEF
VALVE
DIRECTIONAL
CONTROL VALVE
CYLINDER
RETURN
LINE
PUMP
RESERVOIR
Figure 3. Basic Hydraulic System Components
7
Activity 1. Hydraulic Trainer Component Identification
Procedure Overview
In this activity, you will identify the components of the
Amatrol 850 Series hydraulic trainer. This activity will
familiarize you with the components used in a hydraulic
system.
❑ 1. Position yourself in front of the Amatrol 850 Series hydraulic
trainer shown in figure 4.
HYDRAULIC
INSTRUMENTATION
MODULE
HYDRAULIC
ACTUATOR
MODULE
BASIC HYDRAULIC
VALVE MODULE
HOSE RACK
HYDRAULIC
POWER
UNIT
Figure 4. Amatrol 850 Series Hydraulic Trainer
❑ 2. Locate the Instrumentation Module.
This includes pressure gauges and a flow meter to monitor your
circuits.
❑ 3. Locate the Actuator Module.
This panel includes two cylinders, a motor, and some valves to
build many types of circuits used in industrial applications.
❑ 4. Locate the Basic Hydraulic Valve Module.
This panel includes several types of valves that you will use to
build circuits. These valves will be connected to the actuators on
the actuator panel.
8
❑ 5. Locate the Hydraulic Power Unit.
This unit has the pump, electric motor, reservoir, and other
components to supply power to the system.
❑ 6. Locate the Hoses.
The hoses will be used to connect the components.
❑ 7. Locate each of the following components on the trainer shown in
figure 5.
Each component’s name is silkscreened next to it on its mounting
panel. Use these labels to identify the location of each component.
COMPONENT
LETTER
PRESSURE GAUGE
MOTOR
CYLINDER
DIRECTIONAL CONTROL VALVE
PRESSURE REDUCING VALVE
FLOW CONTROL VALVE
CHECK VALVE
B
D
F
E
A
A
G
B
C
Figure 5. Identifications of Various Hydraulic Components
9
OBJECTIVE 3
DEFINE HYDRAULIC PRESSURE AND GIVE ITS
UNITS OF MEASUREMENT
An important concept in hydraulics is pressure. Pressure is the
intensity of force, and is created when a force from one object acts over
an area of another object.
For example, in figure 6, the weight of the box creates a total force
of 32 Newtons on the surface upon which it is resting. However, the
force is actually distributed evenly over the entire area of 4 square
meters. This means that a percentage of the total force (32 N) acts on
each square meter of the surface. In this case, it would be 8 Newtons for
each square meter (32 ÷ 4 = 8). The pressure is said to be 8 Newtons per
square meter or 8 N/m2.
WEIGHT OF
CUBE 32N
PRESSURE
8 N/m2
1 SQUARE
METER
2m
2m
Figure 6. Pressure is Determined by the Force and Area
10
The pressure created by any force can easily be calculated by
dividing the total force by the total area as the following formula shows.
The most common units in the U.S. Customary system are inches and
pounds. This creates the unit of pressure called psi or lbs/in2 (pounds per
square inch). The most common units in the S.I. metric system are
Newtons and meters. This creates a unit of pressure called a Pascal (Pa).
FORMULA: PRESSURE / FORCE / AREA RELATIONSHIP
Pressure =
Force
Area
S.I. Units:
Pressure = Pascals (Pa), which is equal to N/m2
Force
= Newtons (N)
Area
= Square Meters (m2)
U.S. Customary Units:
Pressure = psi (lbs/in2)
Force
= Pounds (lbs)
Area
= Square Inches (in2)
A Pascal is equal to 1 N/m2.
To further see how pressure and force are different but related, look at
figure 7. When the weight is laid on its side, it creates a pressure of 2 N/m2
(5 ÷ 2.5 = 2). But when it is laid on its end, the pressure is 5 N/m2 (5 ÷ 1 =
5). The same force creates two different pressures by acting over different
amounts of area.
This same result occurs in people’s shoes. If a woman with a
LOW PRESSURE
HIGH PRESSURE
5N
WEIGHT
5N
WEIGHT
A1 = 2.5 m2
NOTE: SHADED AREAS REPRESENT
AREAS IN CONTACT WITH
THE SURFACE
A2 = 1 m2
Figure 7. Force vs. Pressure
11
high-heeled shoe steps on you, it hurts much more than if it is a flat-soled
shoe. This is because the pressure is higher with the smaller heel.
In addition to mechanical pressure, as shown in figure 7, hydraulic
fluid also produces a pressure called fluid pressure. A simple way to
create fluid pressure is to place a weight on a container filled with liquid,
as shown in figure 8. To support the weight, the fluid generates a
pressure in the container.
The fluid pressure will be the same at every point in the liquid inside
the bottle as long as the liquid is not moving. A Frenchman named Blaise
Pascal discovered this concept in the seventeenth century. It is called
Pascal’s Law. More about Pascal’s Law will be covered in a later LAP.
10 N
LOAD
FLUID
PRESSURE
STOPPER
AREA = 0.1m 3
OIL
BOTTLE
Figure 8. Fluid Pressure Created by a Weight Placed on a Container
The amount of fluid pressure created in the container is determined
using the P=F/A formula, where the force is the weight and the area is
the area of stopper. In figure 8, for example, the pressure is 100 N/m2 (10
÷ 0.1 = 100).
The concept shown in figure 8 actually has an application with
hydraulic cylinders which will be discussed later.
12
SKILL 1
READ A HYDRAULIC PRESSURE GAUGE
Procedure Overview
A pressure gauge indicates the pressure in the
hydraulic system. Technicians read pressure gauges in
industry to determine if the machine is operating correctly.
In this procedure, you will learn how to read a pressure
gauge using the Amatrol hydraulic trainer.
❑ 1. Locate Gauge A on the hydraulic trainer’s instrumentation panel,
as shown in figure 9.
GAUGE A
Figure 9. Gauge A Location
Most pressure gauges have a face plate graduated in either U.S.
Customary units (psi) or metric units (Pascals). A pointer rotates
around the scaled face plate as the pressure changes to indicate the
pressure in the system.
13
Gauge A actually has two scales to enable it to indicate both
English units and metric units. The outer black scale indicates
units of psi, and the inner red scale indicates kilo Pascals (kPa).
One kPa is equal to 1000 Pascals, while 6.9 kPa is equal to 1 psi.
Each scale is graduated with a series of numbers ranging from 0 to
some number. In the case of Gauge A, the maximum reading
possible is 7000 kPa or 1000 psi. This maximum reading is
commonly called the range of the gauge.
To read a pressure gauge, you only have to look at the number on
the red or black scale to which the pointer points. For example, the
pressure reading, shown for the gauge in figure 10, is 200 psi or
about 1400 kPa.
500
60
0
0
40
400
0
300
0
200
0
30
0
0
70
90
0
0
10
600
0
1000
800
200
0
500
00
70
00
10
0
kPa
0
psi
Figure 10. Typical Gauge Reading
NOTE
Sometimes, gauges may show a kPa scale labeled “100 ×
kPa” at the bottom of the gauge face. This means that the kPa
readings you take from the scale must be multiplied by 100 to
get the actual reading. For example, a reading of 9 is really 900
kPa and a reading of 70 is actually 7000 kPa.
14
If the pointer points to a position between two numbers, as shown
in Gauge 1 in figure 11, read the gauge to the nearest graduation.
For example, in Gauge 1 of figure 11, the pointer is positioned
between 2000 and 3000 kPa. Note that there are 10 graduations
between 2000 and 3000. This means the value of each graduation
is 100 kPa. Since the pointer is pointing to the first graduation, the
pressure being indicated is 2100 kPa.
❑ 2. Practice your ability to read a pressure gauge by determining the
readings for each gauge shown in figure 11.
GAUGE 2
500
30
0
200
0
30
0
200
1000
0
10
30
0
200
0
200
0
1000
00
10
1000
200
0
10
00
70
0
00
70
0
00
10
0
200
0
30
0
1000
kPa
0
200
0
1000
00
70
0
00
10
0
0
30
0
30
0
200
200
0
10
90
0
90
0
0
10
600
0
1000
800
200
0
500
800
600
0
90
0
00
70
0
0
psi
0
70
0
500
800
600
0
kPa
400
0
0
300
0
70
0
500
00
10
0
0
psi
60
0
0
40
400
0
0
300
0
70
200
0
500
60
0
0
40
400
0
90
0
0
200
800
6 00
0
90
0
0
10
0
500
800
6 00
0
90
0
GAUGE 6
500
60
0
0
10
0
70
0
500
800
600
0
psi
GAUGE 5
500
0
40
kPa
kPa
psi
GAUGE 4
400
0
0
300
0
70
0
500
kPa
psi
0
300
400
0
0
300
0
70
kPa
60
0
0
40
00
70
400
0
0
300
500
60
0
0
40
00
70
60
0
0
40
00
10
500
GAUGE 3
00
10
GAUGE 1
psi
Figure 11. Various Gauge Readings
15
GAUGE
PRESSURE
(psi/kPa)
1
/
2
/
3
/
4
/
5
/
6
/
The answers for these are Gauge 1 = 300 psi / 2100 kPa, Gauge 2
= 150 psi / 1000 kPa, Gauge 3 = 250 psi / 1700 kPa, Gauge 4
= 70 psi / 500 kPa, Gauge 5 = 160 psi / 1100 kPa, Gauge 6 = 400
psi / 2800 kPa.
❑ 3. Now locate Gauge S on the hydraulic trainer’s power unit shown
in figure 12. The pointer on this gauge should be indicating 0, as
shown in figure 12.
Notice that the unit of bar is used instead of the kPa unit for one of
the scales. A bar is approximately equal to 1 standard atmosphere,
which is about 14.7 psi or 100 kPa. To convert this scale to kPa,
just add two zeroes to the reading. For example, 10 bar is
approximately 1000 kPa.
GAUGE S
Figure 12. Gauge S Location
16
❑ 4. Determine the following about Gauge S.
A. Full Scale Reading________________psi ______________kPa
B. Major Graduation Unit_____________psi ______________kPa
C. Minor Graduation Unit_____________psi______________kPa
You should find that the full scale (FS) reading is 1000
psi/7000 kPa, major unit 100 psi/1000 kPa, and minor unit 20
psi/100 kPa.
It is important to know that pressure gauges are not perfectly
accurate. All gauges have an error. Manufacturers state the
error as a percent of the FS reading in their catalog data sheet.
For example, if Gauge S has an error of ±5% FS (full scale),
then the actual pressure could be different from the reading by
50 psi (0.05 × 1000). A good pressure gauge should have a FS
reading error of 0.5% or 1%.
A point you should also keep in mind is that the amount of
error does not depend on the actual pressure reading. For
example, if the pressure gauge’s FS is 1000 psi and its error is
±5% of FS (i.e. 50 psi in this case), the error is ±50 psi whether
the actual reading is 200 psi or 1000 psi. This means that the
gauge is not very accurate if the pressure is at the bottom of its
range.
17
SEGMENT 1
SELF REVIEW
1. The power output device of a hydraulic system is known as
the _____________.
2. Hydraulics uses a(n) _______________ to transmit power.
3. Pressure is a measure of __________ intensity.
4. The units of pressure measurement used in the S.I. system
are _______.
5. The actuator converts ______ energy into ________ energy.
18
SEGMENT 2
POWER UNIT OPERATION
OBJECTIVE 4
DESCRIBE THE OPERATION OF A HYDRAULIC POWER UNIT
The hydraulic components of most machines are grouped into two
parts: the actuator/control valves on the machine structure and the power
unit. The main components of the power unit are the pump, reservoir,
and the prime mover (usually an electric motor), which drives the pump.
ACTUATOR
HYDRAULIC
POWER UNIT
ACTUATOR
CONTROL
VALVES
Figure 13. Hydraulic Press with Separate Power Unit
19
In addition to the main components, most hydraulic power units
include devices to monitor the operation (e.g. pressure gauge), filters to
clean the oil, a relief valve for safety, and some means to start and stop
the unit.
When the prime mover on the power unit is started, it rotates the
shaft of the pump. This causes the pump to draw oil from the reservoir
through a filter and push it out to the system through the supply line, as
shown in figure 14. Oil that leaves the actuators comes back to the
reservoir through the return line.
It is the job of the power unit to not only produce a flow of oil to the
system, but to make sure it is clean and not too hot. To clean the oil,
most power units have a suction filter and a return filter. To cool the oil,
many power units use a heat exchanger that uses cool water or air.
However, some power units allow the oil to cool by having a large
reservoir.
SUPPLY LINE
RETURN LINE
OIL FLOW TO VALVE
AND ACTUATORS
OIL RETURNING
FROM ACTUATORS
RETURN
FILTER
GAUGE
SAFETY
RELIEF
VALVE
OIL
COOLER
ELECTRIC
MOTOR
PUMP
SUCTION
FILTER
RESERVOIR
Figure 14. Basic Operation of the Power Unit
20
Activity 2. Identification of 850 Power Unit Components
Procedure Overview
It is very important to know every aspect of the
operation of the hydraulic power unit. In this activity, you
are going to begin learning about the 850 Series hydraulic
power unit by inspecting it. This unit is a small industrial
model.
❑ 1. Locate the Hydraulic Power Unit on the 850 Series trainer shown
in figure 15.
NOTE: The Pump,
Suction Line and
Suction Strainer
Are Located Inside
The Reservoir of
The Power Unit
RETURN LINE
ELECTRIC MOTOR
PRESSURE GAUGE
SUPPLY LINE
RELIEF VALVE
FILLER/BREATHER
LIQUID LEVEL GAUGE
ELECTRICAL
STARTER BOX
RESERVOIR
Figure 15. The 850 Series Hydraulic Power Unit
21
SHUTOFF
VALVE
SUPPLY
LINE
ELECTRIC
MOTOR
SUPPLY
MANIFOLD
PRESSURE
GAUGE
RETURN
LINE
HYDRAULIC
PUMP
RETURN
MANIFOLD
FILLER/
BREATHER
RELIEF
VALVE
SUCTION
LINE
SUPPLY
LINE
SUCTION
STRAINER
LIQUID
LEVEL
GAUGE
RESERVOIR
RETURN
LINE
Figure 16. Pictorial of the 850 Series Hydraulic Power Unit
❑ 2. Locate the Electric Motor.
Most industrial hydraulic power units get their energy from a
constant-speed electric motor. The electric motor’s shaft is
connected to the shaft of the hydraulic pump through a coupling.
❑ 3. Locate the Hydraulic Pump.
In this case, you will not be able to actually see it because it is
mounted inside the reservoir.
The hydraulic pump supplies oil to the hydraulic system. When the
electric motor drives the pump shaft, the pump draws oil from the
reservoir into its inlet and discharges it into the system from its
outlet. The power unit design in the 850 power unit is a vertical
design where the electric motor and pump are mounted vertically.
The pump is located underneath the electric motor inside the
reservoir, as shown in figure 17.
22
HYDRAULIC
PUMP
SUCTION
FILTER/
STRAINER
SUCTION
LINE
SUPPLY/
PRESSURE
LINE
RETURN
LINE
Figure 17. Hydraulic Pump of 850 Power Unit
❑ 4. Locate the Reservoir.
The reservoir’s main purpose is to contain oil not being used by
the circuit. It also allows the oil to cool and dirt to settle before the
oil re-enters the circuit. The 850 unit is a 10-gallon unit.
❑ 5. Identify the Suction Line.
This line is connected to the pump’s inlet. It is the line through
which the pump draws oil from the tank.
❑ 6. Locate the Supply Line.
This line is connected to the pump’s outlet. It is the line through
which the oil flows to the system. This line is sometimes called the
pressure line.
The supply line runs through the relief valve’s manifold block and
comes out of a port marked P. See if you can locate the P port on
the relief valve.
The supply line of the 850 power unit then runs to the supply
manifold. This manifold is a machined block with four ports or
connections that are all connected to the supply line. This allows
four separate hoses to easily connect to the pump to supply four
separate circuits.
It is also important to note that the 850 unit’s supply manifold has
a shutoff valve connected between it and the pump. This valve’s
main function is to block power to the circuit during startup of the
power unit.
23
❑ 7. Locate the Return Line.
This is the line through which oil returns from the system to the
reservoir.
The return line of the 850 power unit runs from the return
manifold to the relief valve’s port marked R. See if you can locate
the R port on the relief valve.
The return manifold allows oil to return to the reservoir through up
to four hoses at the same time.
NOTE
It is important to note that the return line and supply lines run
straight through the relief valve block. The relief valve is actually
mounted in the block so that it provides a way to let the supply
line oil short circuit to the return line. These two lines are not
actually running through the relief valve itself, only through the
block.
❑ 8. Locate the Relief Valve.
The relief valve limits system pressure to safe levels. Its pressure
setting is adjusted using the black knob located on the side of the
valve’s body.
❑ 9. Locate the Pressure Gauge.
The pressure gauge is connected through the body of the relief
valve to the pump’s outlet. It reads the oil pressure at the outlet of
the pump. This is also the pressure in the supply manifold.
❑ 10. Locate the Suction Strainer.
The suction strainer is installed in the suction line at the inlet to the
pump and located beneath the surface of the oil. It protects the
pump from taking in any harmful dirt particles that may be in the
reservoir.
❑ 11. Locate the Filler/Breather.
The filler/breather performs two functions for the hydraulic power
unit. First, it has a cap that unscrews to allow the reservoir to be
filled with oil. You will notice it also has a protective screen
attached to the reservoir to keep any large pieces of dirt from
entering the hydraulic system.
The second function served is to allow air to enter or exit the
reservoir. This is necessary because the oil level rises and falls
slightly at various times during circuit operation. As you will soon
learn, the air pressure in the reservoir must be kept near
atmospheric pressure. The filler/breather allows air to pass through
air openings in its cap to balance the pressure. These openings
have filters over them to help keep out dirt.
24
❑ 12. Locate the Liquid Level Gauge.
The liquid level gauge indicates the level of the oil in the reservoir.
It is attached to the outside of the reservoir and has a port
connected through the reservoir to the oil.
❑ 13. Locate the Return Filter.
The return filter is connected in the return line to remove dirt that
has been obtained as the oil flowed through the components in the
system. This filter is not always needed on small power units like
the 850 unit.
25
SKILL 2
READ THE LIQUID LEVEL AND TEMPERATURE
IN THE RESERVOIR
Procedure Overview
In this procedure, you will check the level and
temperature of the oil in the reservoir of the hydraulic
trainer.
❑ 1. Locate the Liquid Level Gauge, shown in figure 18, on the
reservoir of the power unit.
The liquid level indicates the quantity of oil available. There are
two marks shown on the gauge: a red mark at the bottom and a
blue or black mark at the top. The oil level must be kept between
these two marks.
Also, there is a thermometer contained inside the liquid level
gauge. This indicates the temperature of the oil in the reservoir. Oil
temperature drastically affects the performance of the hydraulic
system. The temperature of the oil should be between room
temperature and 130°F/54° C.
BLACK OR BLUE MARK
C
F
THERMOMETER
RED MARK
Figure 18. Liquid Level Gauge
❑ 2. Read the liquid level and describe the level relative to the two
marks.
_______________(below red mark, in between, above black mark)
You should observe that it is in between the marks. If it is not,
check with your instructor to correct this.
❑ 3. Read the oil temperature and record below.
______________________________________________(°F / ° C)
You should observe that it is near room temperature.
26
SKILL 3
OPERATE A HYDRAULIC POWER UNIT
Procedure Overview
For most of the activities in this manual, you will use
the hydraulic power unit to supply power to your circuit. In
order to safely use this power supply, there are very
specific steps that must be followed. These steps are
basically the same ones you would use with any industrial
machine. In this procedure, you will perform these steps to
check out and then start up a hydraulic power unit.
❑ 1. Before starting the power unit, perform the following checkout
procedures:
A. Check the oil level in the reservoir by looking at the liquid
level sight glass. If the oil is below the red mark, fill the
reservoir with clean oil until the oil level rises to the desired
level between the two marks. To do this, unscrew the filler
breather cap and pour oil into the reservoir.
B. Press the red pushbutton labeled Stop on the power unit’s
motor starter to make sure the starter is in the off position.
C. Plug the power cord of the power unit’s electric motor into a
wall outlet.
D. Set the power unit’s relief valve to minimum starting pressure by
turning its knob counterclockwise (CCW), as shown in figure 19.
COUNTER CLOCKWISE (CCW)
DECREASES
PRESSURE SETTING
CLOCKWISE (CW)
INCREASES
PRESSURE SETTING
Figure 19. Relief Valve Pressure Setting Knob
27
❑ 2. Press the green Start button to start the power unit.
The electric motor should start running. The pump will then pump
oil. Since no hoses are connected to the supply manifold the
pump’s flow returns to the reservoir through the relief valve, as
shown in figure 20.
Because the relief valve is turned to its minimum pressure setting,
you should observe a near zero pressure at Gauge S. This is the
pressure required to open the relief valve.
RETURN
MANIFOLD
SUPPLY
MANIFOLD
RELIEF
VALVE
LOW
PRESSURE
PUMP
OIL FLOWS
THROUGH
VALVE
RESERVOIR
Figure 20. Pump Flow Returning to Reservoir Through Relief Valve
28
❑ 3. Turn the black knob on the relief valve clockwise until the
pressure of Gauge S reads 200 psi/1380 kPa.
The flow from the pump should still flow through the relief valve,
as shown in figure 21. However, the relief valve’s setting causes
the pump to push harder to open it. This causes the higher
pressure.
RETURN
MANIFOLD
SUPPLY
MANIFOLD
RELIEF
VALVE
200 psi /
1380 kPa
PUMP
OIL FLOWS
THROUGH
VALVE
RESERVOIR
Figure 21. Pump Flow Returning to Reservoir at Higher Pressure
❑ 4. Now turn the adjustment knob clockwise to 500 psi/3447 kPa.
This pressure is the maximum rated pressure of the power unit.
❑ 5. Readjust the pressure back to 200 psi/1380 kPa by turning the
adjustment CCW.
To accurately obtain this pressure, adjust below 200 psi/1380 kPa
and then adjust back to the desired pressure.
❑ 6. Turn the relief valve knob fully CCW to reduce the relief valve’s
pressure to minimum.
CAUTION
Before turning off the power unit, the relief valve should be
reduced to the minimum pressure as you have just done. If this
is not done, the pressure in the system can cause the pump to
turn backwards and damage it!
❑ 7. Press the red Stop pushbutton on the motor starter to turn off the
power unit.
29
SEGMENT 2
SELF REVIEW
1. To increase the pressure setting of a relief valve, turn the
adjustment knob _____________.
2. Power units normally are started and stopped with the relief
valve set at _____________.
3. The purpose of a relief valve is to ____________ system
pressure.
4. The liquid level gauge often gives you the oil’s __________
as well as its level.
5. The ____________ is where the oil can be poured into the
reservoir to refill it.
6. Pumps always have a(n) __________ attached to their
suction lines to clean the oil.
7. The main components of a hydraulic power unit are the
pump, reservoir, and __________.
30
SEGMENT 3
CIRCUIT CONNECTIONS
OBJECTIVE 5
DESCRIBE THE FUNCTION OF A HYDRAULIC SCHEMATIC
Before we look at more complex hydraulic circuits, we first need to
look at the way these components are represented in a diagram. A fluid
power diagram shows how the components in a circuit are connected so
that we can understand what the circuit does and how it works.
So far, the hydraulic diagrams have been pictorial, where actual
pictures are used. While pictorials allow us to easily see what the devices
look like, they are very time consuming to draw and actually harder to
use. To solve this problem, schematic diagrams are used.
A schematic diagram is a form of visual shorthand where standard
symbols represent each component. It shows all the components in a
circuit and their interconnections. Schematic diagrams are usually drawn
in the normal or de-energized condition.
An example of a typical hydraulic schematic that uses standard
symbols is shown in figure 22.
M
Figure 22. Typical Hydraulic Schematic
31
As you learn about each new hydraulic component, you will learn
the symbol for each device. Most hydraulic symbols use an elementary
form to identify the general function of the component. These forms are
circles, squares, rectangles, triangles, arcs, arrows, lines, dots and ovals,
as shown in figure 23. These basic symbol forms are combined together
to form symbols of various components.
SYMBOL
SYMBOL
ROTATING DEVICE
VARIABLE
VALVE
RESTRICTION
CONDITIONING DEVICE
LINES CONNECTED
CYLINDER
SPRING
ACCUMULATOR
BLOCKED LINE
CONDUCTOR
BLOCKED LINE
FLOW DIRECTION
Figure 23. Elementary Forms of Symbols
As you will see throughout these LAPs, the solid flow direction
arrow (triangle) is also used as a shortcut to indicate a partial circuit.
This allows you to show only the components and circuit necessary
without having to draw the complete circuit diagram.
Three standards that are most often referenced for symbols are those
developed by the National Fluid Power Association (NFPA), American
National Standards Institute (ANSI), and the International Organization
for Standardization (ISO).
The organization uses ISO instead of IOS because, although not a
correct acronym, it is easier to remember. ISO is from the Greek word
“isos,” meaning equal.
The United States uses NFPA and ANSI standards. The rest of the
world, as well as the U.S., uses the ISO standard.
NOTE
As you progress through the rest of this LAP, you will learn
the symbol for each component and how to read schematics that
contain them.
32
OBJECTIVE 6
DESCRIBE THE FUNCTION OF A HYDRAULIC
QUICK-CONNECT FITTING AND GIVE ITS SCHEMATIC SYMBOL
Hydraulic systems often use flexible hoses. Sometimes these hoses
use quick-connect fittings to connect them to the components. As its
name implies, this style of fitting allows fast and easy assembly and
disassembly of circuits.
Quick-connect fittings consist of a male-end fitting and a female-end
fitting, as shown in figure 24. These fittings snap together without
special tools.
Industry uses quick-connect fittings when there is a frequent need to
disconnect a hose. An auxiliary power unit for jet aircraft is an example.
FEMALE QC
FITTING
MALE QC
FITTING
Figure 24. Quick-Connect Fittings
The schematic symbol for two quick-connect fittings which are
connected is shown in figure 25. Each fitting shown has a valve called a
check valve which closes when the fittings are disconnected to keep oil
from leaking out.
ONE END
WITH
CHECK VALVE
SHOWS
CONNECTION
ONE END
WITH
CHECK VALVE
Figure 25. Schematic Symbol for Quick-Connect Fittings
33
SKILL 4
CONNECT AND DISCONNECT A HYDRAULIC HOSE
THAT USES QUICK-CONNECT FITTINGS
Procedure Overview
In this procedure, you will learn to use quick-connect
fittings to connect components. To do this, you will hook
up a pressure gauge.
❑ 1. Perform the following steps to inspect the quick-connect on the
850 hydraulic trainer.
Because you will need to change circuits frequently, the 850 basic
hydraulic system uses flexible hydraulic hoses and quick-connect
fittings.
A. Locate a quick connect fitting on the supply manifold, as
shown in figure 24. This is a male fitting.
One important feature of hydraulic quick-connect fittings is
they have built in valves to keep oil from leaking out of the
hose or components when the hose connection is released. This
avoids messy oil spills. When the male and female ends are
connected, they each open their valves to allow oil to flow
freely.
B. Try pressing the top of the male fitting with your thumb to see
if you can open the valve.
C. Now locate a hose and inspect its quick-connect fitting. This is
a female fitting.
D. Try pressing a ballpoint pen on the bottom of the inside of the
fitting to see if you can open its valve.
As you can see, both the male and female fittings have valves
to keep the oil from leaking. When these two fittings are
connected to each other, their valves are forced open so that oil
can flow through.
34
❑ 2. Perform the following substeps to set up the circuit shown in
figure 26.
HYDRAULIC INSTRUMENTATION PANEL
GAUGE A
GAUGE B
FLOW
METER
GAUGE C
SUPPLY
MANIFOLD
RELIEF \ SEQUENCE
VALVE
PRESSURE REDUCING
VALVE
1
SHUTOFF
VALVE
1
2
2
3
3
NEEDLE
VALVE
A
B
RETURN
MANIFOLD
IN
D.C.V.
#1
CHECK VALVE #1
A
B
OUT
B
A
CHECK VALVE #2
B
A
BASIC HYDRAULIC VALVE MODULE
Figure 26. Circuit Setup: Pressure Gauge A Connected to Supply
Manifold
A. Locate a flexible hose from the trainer’s hose storage area.
Make sure it is long enough to reach from the supply manifold
to Gauge A.
35
B. Grasp the female fitting on the hose and pull back on its collar,
as shown in figure 27.
COLLAR
Figure 27. Q.C. Collar Pulled Back
C. While holding the collar back, push the female end firmly onto
the male end of the pressure gauge and release the collar. Your
completed assembly should appear as shown in figure 28.
Figure 28. Hose Connected to Pressure Gauge
D. Now check your connection by pulling firmly on the hose.
If you connected the fittings properly, the hose should not pull
loose.
36
❑ 3. Repeat step 2 to connect the other end of the hose to the supply
manifold, as shown in figure 26.
❑ 4. Perform the following checkout procedures before starting the
hydraulic power unit.
A. Check the oil level. Fill if necessary.
B. Press the stop pushbutton on the motor starter to make sure it is
in the off position.
C. Plug in the power cord to a wall outlet.
D. Reduce the relief valve to its minimum pressure setting (turn
CCW fully).
❑ 5. Turn on the power unit.
❑ 6. Open the shutoff valve on the supply manifold by turning its
handle, as shown in figure 29. This will connect the flow of oil
from the pump to Gauge A.
HANDLE IN OPEN POSITION
HANDLE IN CLOSED POSITION
Figure 29. Shutoff Valve in Opened and Closed Positions
❑ 7. Turn the relief valve’s adjustment knob CW until the pressure at
Gauge S on the power unit reads 100 psi/690 kPa.
❑ 8. Record the pressure indicated at Gauge A.
Gauge A = _____________________________________(psi/kPa)
It should be close to the reading at Gauge S. If it is, you have
correctly connected the hose and the gauges are working correctly.
Gauge S reads 500 psi/3447 kPa.
❑ 10. Record the pressure indicated at Gauge A.
Gauge A = _____________________________________(psi/kPa)
Again, both gauges should closely agree.
37
❑ 11. Turn the relief valve’s adjustment CCW fully to reduce the
pressure to a minimum.
❑ 12. Turn off the power unit and close the shutoff valve.
❑ 13. Disconnect the hose between the gauge and the manifold using the
following substeps.
A. Put your hand around the collar of the hose fitting.
B. Push the two fittings together and hold them.
C. While holding, pull back on the collar with your fingers and
then pull the hose to release it.
NOTE
Make sure you push the two fittings together before pulling the
collar.
If there is pressure trapped in the system, connecting and
disconnecting hydraulic quick-connects can be difficult if not
impossible. If you are unable to easily connect or disconnect a
hose equipped with quick-connects, there is probably pressure
trapped in the circuit. This pressure should be removed before
you make or break the connection.
❑ 14. Use the following substeps to verify the difficulty of connecting
the quick-connect fitting under pressure.
A. Turn on the power unit.
B. Turn the relief valve’s adjustment knob CW until the pressure
at Gauge S on the power unit reads 200 psi/1380 kPa.
C. Open the shutoff valve on the supply manifold.
This will connect the supply manifold fittings to the outlet of
the pump.
D. Close the shutoff valve.
Pressure will now be trapped in the manifold.
E. Turn the relief valve’s adjustment CCW fully to reduce the
F. Turn off the power unit.
G. Connect one end of a hose to Gauge A and attempt to connect
the other end to the supply manifold.
You should find it difficult to connect the hose to the supply
manifold because there is trapped pressure. At higher pressures,
you might not even be able to make the connection.
38
❑ 15. Open the shutoff valve and connect the other end of the Gauge A
hose to the supply manifold if not already connected.
You should now see that the hose can easily be connected to the
manifold because the pressure has been lowered.
❑ 16. Now use the following substeps to verify the difficulty of
disconnecting the quick-connect fitting under pressure.
A. Turn on the power unit.
B. Turn the relief valve adjustment knob CW until the pressure at
C. Open the shutoff valve on the supply manifold. This will
connect the pump to Gauge A.
You should observe 200 psi/1380 kPa on Gauge A.
D. Close the shutoff valve.
E. Turn the relief valve’s adjustment CCW fully to reduce the
F. Turn off the power unit.
You should observe approximately 200 psi/1380 kPa on Gauge
A because pressure has been trapped between the shutoff valve
and the gauge.
G. Try to disconnect the hose from the supply manifold.
You should find it difficult to disconnect the hose.
H. If disconnected, reconnect the hose to the manifold.
❑ 17. Open the shutoff valve. Gauge A pressure should drop to zero.
❑ 18. Now disconnect the hose.
With no pressure in the hose it should be easily disconnected.
39
OBJECTIVE 7
DESCRIBE THE FUNCTION OF A TEE AND GIVE
ITS SCHEMATIC SYMBOL
There are many times when you will need to connect two circuits to
the same supply line. A single fitting called a tee (and shaped like a “T”)
provides this connection.
The 850 hydraulics system includes three fitting tees equipped with
quick-connect fittings: two ends are male and one end is female, as
shown in figure 30. These fittings allow you to quickly connect these
components together.
SCHEMATIC
SYMBOL
Figure 30. Tee Equipped with Quick-Connect Fittings and Schematic
BRANCH A
SUPPLY
LINE
TEE
BRANCH B
Figure 31. Tee Connection to Two Branch Circuits
40
SKILL 5
USE A TEE TO CONNECT TWO
CIRCUIT BRANCHES TOGETHER
Procedure Overview
In this procedure, you will connect two pressure
gauges to the same supply line using tee fittings. This
procedure will help you better understand how to use tees
in a circuit.
❑ 1. Set up the circuit shown in figure 32.
In this circuit, both gauges are connected to the supply line by a
fitting tee. This will allow both pressure gauges to read the
pressure at the manifold.
GAUGE A
GAUGE B
FLOW
METER
GAUGE C
TEE
SUPPLY
MANIFOLD
RELIEF \ SEQUENCE
VALVE
PRESSURE REDUCING
VALVE
1
SHUTOFF
VALVE
1
2
MANIFOLD
TEE
FITTING
2
3
3
NEEDLE
VALVE
A
B
RETURN
MANIFOLD
IN
D.C.V.
#1
CHECK VALVE #1
A
B
OUT
B
A
CHECK VALVE #2
B
A
Figure 32. Pictorial of Gauges A and B Connected to Supply Using a
Separate Fitting Tee
41
hydraulic power unit.
in the off position.
CCW fully).
❑ 4. Open the shutoff valve on the supply manifold.
This will connect the tee fitting to the outlet of the pump.
Record the pressures indicated at Gauges A and B.
Gauge A _______________________________________(psi/kPa)
Gauge B _______________________________________(psi/kPa)
Both gauges should be close to the reading at Gauge S. If they are,
you have correctly connected a separate tee fitting in the circuit.
Gauge A _______________________________________(psi/kPa)
Gauge B _______________________________________(psi/kPa)
42
❑ 9. Now locate the tee fittings attached to each gauge, as shown in
figure 33.
These are called gauge block tees. They do the same thing as the
loose fitting tee you just used. They are tees machined from blocks
of aluminum.
GAUGE A
GAUGE B
FLOW
METER
GAUGE C
TEE
MACHINED
INSIDE OF
BLOCK
GAUGE
BLOCK
TEE
SUPPLY
MANIFOLD
RELIEF \ SEQUENCE
VALVE
PRESSURE REDUCING
VALVE
1
SHUTOFF
VALVE
1
2
2
3
3
NEEDLE
VALVE
A
B
RETURN
MANIFOLD
IN
D.C.V.
#1
CHECK VALVE #1
A
B
OUT
B
A
CHECK VALVE #2
B
A
Figure 33. Pictorial of Gauges A and B Attached to the Supply Line
Using a Gauge Block Tee
❑ 10. Set up the circuit shown in figure 33.
In this circuit, gauge block A’s tee is used to connect Gauges A
and B to the supply line. This is the same circuit you connected in
step 1 with the separate tee.
The gauge block tees are attached to the gauges to save you setup
time. The pressure gauge is almost always connected to the circuit
through a tee.
❑ 12. Open the shutoff valve on the supply manifold.
This will connect gauge block A’s tee to the outlet of the pump.
43
❑ 14. Record the pressures indicated at Gauges A and B.
Gauge A _______________________________________(psi/kPa)
Gauge B _______________________________________(psi/kPa)
Both gauges should be close to the reading at Gauge S. If they are,
you have correctly connected Gauge A’s tee block in the circuit.
❑ 16. Record the pressures indicated at Gauges A and B.
Gauge A _______________________________________(psi/kPa)
Gauge B _______________________________________(psi/kPa)
Again, all gauges should closely agree.
❑ 19. Now change the circuit to the one shown in figure 34.
In this circuit, gauge block A’s tee is connected to the other side of
gauge block B’s tee.
The purpose of testing this circuit is to show you that both sides of
the gauge block tee are connected to each other and to the gauge
port.
GAUGE A
GAUGE B
FLOW
METER
GAUGE C
TEE
MACHINED
INSIDE OF
BLOCK
GAUGE
BLOCK
TEE
SUPPLY
MANIFOLD
PRESSURE REDUCING
VALVE
RELIEF \ SEQUENCE
VALVE
1
SHUTOFF
VALVE
1
2
2
3
3
NEEDLE
VALVE
A
B
RETURN
MANIFOLD
IN
D.C.V.
#1
CHECK VALVE #1
A
B
OUT
B
A
CHECK VALVE #2
B
A
Figure 34. Pictorial of Gauges A and B Connected to the Supply Line
Using a Gauge Block Tee
44
❑ 20. Turn on the power unit and open the shutoff valve on the supply
manifold.
This again will connect gauge block A’s tee to the outlet of the
pump.
❑ 21. Turn the relief valve’s pressure adjustment knob CW until the
pressure at Gauge S on the power unit reads 100 psi/690 kPa.
Gauge A _______________________________________(psi/kPa)
Gauge B _______________________________________(psi/kPa)
Both gauges should be close to the reading at Gauge S.
Gauge A _______________________________________(psi/kPa)
Gauge B _______________________________________(psi/kPa)
❑ 25. Disconnect the two hoses and store them.
45
OBJECTIVE 8
DESCRIBE THE OPERATION OF A PRESSURE GAUGE
AND GIVE ITS SCHEMATIC SYMBOL
The most common type of pressure gauge is the bourdon tube gauge,
as shown in figure 35. The main component of a bourdon tube is a
curved tube that works much like a party roll up horn. The curved tube in
the bourdon tube gauge straightens slightly when exposed to fluid
pressure. This causes its mechanical linkage to move the pointer
indicating the amount of pressure in the tube. The higher the pressure the
more the tube straightens and the more the pointer rotates.
1500
1000
2000
500
2500
3000
0
POINTER
BOURDON
TUBE
SCALE
LINKAGE
FLUID IN
SYMBOL
Figure 35. Bourdon Tube Gauge and Symbol
46
SEGMENT 3
SELF REVIEW
1. A(n) _____________________ is a form of visual shorthand
that makes hydraulic circuits easier to draw and read.
2. The worldwide standard for hydraulic symbols is developed
by the ___________.
3. A quick-connect fitting is used whenever there is a need to
______________.
4. Two branch circuits are connected with a(n) ____________.
5. A(n) ________________ pressure gauge uses a curved tube
to indicate pressure.
47
SEGMENT 4
BASIC CYLINDER CIRCUITS
OBJECTIVE 9
DESCRIBE THE FUNCTION OF A HYDRAULIC CYLINDER
AND GIVE AN APPLICATION
A hydraulic cylinder is an actuator that converts fluid power into
mechanical power in the form of straight-line motion of a rod. A typical
cylinder is shown in figure 36.
Figure 36. A Typical Hydraulic Cylinder
48
Applications commonly use hydraulic cylinders for high force and
straight-line motion. One example is a plastic injection molding machine
like the one shown in figure 37.
Figure 37. Injection Molding Machine
49
Another example is a hydraulic press as shown in figure 38. Presses
forge parts under high pressure and perform many other tasks.
Figure 38. Hydraulic Press
50
OBJECTIVE 10
DESCRIBE THE OPERATION OF A DOUBLE-ACTING
CYLINDER AND GIVE ITS SCHEMATIC SYMBOL
A hydraulic cylinder consists of a piston/rod assembly that moves
inside a barrel-shaped body. The most common type of cylinder is a
double-acting cylinder like the one shown in figure 39. This type has two
ports through which oil can enter. When oil flows into the cap end, the
cylinder rod extends. The cylinder rod retracts when oil flows into the
rod end.
This operation will be explained in more detail in the following
activity.
PORT
B
PORT
A
ROD
PISTON
BODY
Figure 39. Basic Parts of a Cylinder
The schematic symbol for a double-acting cylinder is shown in
figure 40.
Figure 40. Schematic Symbol of Double-Acting Cylinder
51
Activity 3. Basic Operation of a Double-Acting Cylinder
Procedure Overview
In this procedure, you will connect and operate a
cylinder by switching two hoses between the ports of the
cylinder. This will demonstrate the basic operation of the
cylinder.
❑ 1. Set up the hydraulic circuit shown in figure 41.
GAUGE A
GAUGE B
FLOW
METER
GAUGE C
SUPPLY
MANIFOLD
RELIEF \ SEQUENCE
VALVE
CYLINDER
PRESSURE REDUCING
VALVE
1
1
2
FLOW
FLOW
CONTROL CONTROL
#1
#2
A
A
2
3
3
NEEDLE
VALVE
B
A
B
MOTOR
B
RETURN
MANIFOLD
IN
D.C.V.
#1
CHECK VALVE #1
A
CYLINDER
HYDRAULIC ACTUATOR MODULE
B
OUT
B
A
CHECK VALVE #2
B
A
Figure 41. Pictorial of a Circuit to Extend a Double-Acting Cylinder
❑ 2. Perform the checkout procedures for the power unit.
B. Press the stop push button on the motor starter to make sure it
is in the off position.
CCW fully).
❑ 3. Close the shutoff valve.
❑ 4. Start the power unit and adjust the relief valve pressure to 100
psi/690 kPa (shown at Gauge S).
52
❑ 5. Open the shutoff valve and observe the operation of the cylinder.
You should see that the flow of oil from the pump causes the
cylinder to extend.
To understand how the cylinder was able to extend, remember that
pressure acts on all surfaces in a closed container with equal force.
However, with a cylinder, one wall of the container, the piston, is able
to move. When oil from the pump enters the cylinder port from the
cap end, the oil presses against the inside surfaces of the cylinder.
This causes the piston to move and extend the rod, as shown in figure
42. As the piston moves, it forces the oil on the other side to be
pushed out of the rod-end port. This oil returns to the reservoir.
OIL IN ROD END
IS FORCED OUT
OIL FLOWING
IN
ROD
EXTENDING
FLUID
PRESSURE
CAP
END
ROD
END
Figure 42. Double-Acting Cylinder Being Extended
At this point, you may be wondering why the oil doesn’t leak out of
the cylinder around the rod. This is because there is a flexible seal
called a rod seal that is placed around the rod, as shown in figure 43.
To hold this seal in place, a rod bushing is needed. This bushing
also acts as a bearing to support the rod as it extends.
PISTON
SEALS
ROD
SEALS
ROD
BUSHING
Figure 43. Seals of a Double-Acting Cylinder
In addition to the rod seal, there are also one or more piston seals.
The piston seals keep oil from leaking around the piston so
pressure can build up to move the load.
53
❑ 6. Reduce the relief valve pressure to minimum.
❑ 8. Now switch the two hoses at the cylinder so the pressure line from
the pump connects to the rod end of the cylinder, as shown in
figure 44.
GAUGE A
GAUGE B
FLOW
METER
GAUGE C
SUPPLY
MANIFOLD
RELIEF \ SEQUENCE
VALVE
CYLINDER
PRESSURE REDUCING
VALVE
1
1
2
FLOW
FLOW
CONTROL CONTROL
#1
#2
A
A
2
3
3
NEEDLE
VALVE
B
A
B
MOTOR
B
RETURN
MANIFOLD
IN
D.C.V.
#1
CHECK VALVE #1
A
CYLINDER
B
OUT
B
A
CHECK VALVE #2
B
A
Figure 44. Pictorial of a Circuit to Retract a Double-Acting Cylinder
54
❑ 9. Turn on the power unit and adjust the relief pressure to 100
psi/690 kPa.
❑ 10. Open the shutoff valve and observe the operation of the cylinder.
You should observe that the cylinder retracts.
The cylinder retracted because the oil from the pump flowed into
the cylinder through the rod-end port, as shown in figure 45. This
causes the piston to move in the other direction and retract the rod.
When this happens, the piston forces the oil in the cap end out of
the cylinder and back to the reservoir.
When the piston reaches the end of travel (fully extended or
retracted), the oil flow in the cylinder stops. The pump flow then
returns to the reservoir through the relief valve.
OIL IN ROD END
IS FORCED OUT
OIL FLOWING
IN
ROD
RETRACTING
CAP
END
ROD
END
Figure 45. Double-Acting Cylinder Being Retracted
❑ 12. Turn off the power unit.
❑ 13. Close the shutoff valve.
❑ 14. Disconnect the two hoses and store them.
55
OBJECTIVE 11
DESCRIBE THE FUNCTION OF A 3-POSITION, 4-WAY DCV
AND GIVE AN APPLICATION
To change the direction of the double-acting cylinder without
moving hoses, as you did in the previous skill, we need a switch that
controls the direction of flow. In fluid power, this switch is called a
directional control valve (DCV), as shown in figure 46. Almost every
hydraulic circuit you see uses one or more hydraulic DCVs.
Applications use 3-position, 4-way DCVs to provide 3-function
control of the cylinder: extend, retract, and stop in mid-position.
Figure 46. 850 Series 3-Position 4-Way Directional Control Valve
56
The DCV on the 850 Series trainer uses a manual handle to operate
it. Construction equipment, like the backhoe shown in figure 47, use
manually-operated DCVs. Most industrial applications, however, use
electrically operated valves. You will learn more about these later.
Figure 47. Backhoe with Manually-Operated DCV
57
OBJECTIVE 12
DESCRIBE THE OPERATION OF A 3-POSITION, 4-WAY DCV
AND GIVE ITS SCHEMATIC SYMBOL
The 3-position, 4-way DCV consists of four main components:
• Valve Body - The valve body has ports drilled in it to provide
flow paths for the fluid. Hydraulic DCV bodies are often made
of cast iron, steel or aluminum.
• Spool - The spool is designed with “lands” that channel the flow
through the valve to specific ports. By shifting position, the flow
paths can be changed.
• Operator - The lever is just one type of operator method of
moving the spool from one position to another. Other ways of
moving the spool include a manual palm button, electrical
solenoid, hydraulic pressure, and pneumatic pressure.
• Springs - A 3-position valve usually has a spring on either side of
the spool to position it in the middle when the operator is not
energized.
CYLINDER
CONNECTIONS
OPERATOR
HANDLE
A
B
SPOOL
LAND
SPOOL
SPRING
P
VALVE
BODY
PRESSURE
CONNECTION
T
TANK
CONNECTION
Figure 48. Main Components of a 3-Position, 4-Way DCV
Notice in figure 48 that the ports are labeled. The P stands for the
pressure or inlet port. The T stands for the tank port. This is the port that
is connected to the reservoir.
There are also two actuator ports labeled A and B. These are usually
connected to the lines going to the cylinder or motor. They allow fluid to
flow to and from the cylinder or motor.
58
Directional control valves are manufactured in many different styles
and sizes with a wide variety of options. One major classification of
directional control valves is by the number of flow paths or ways
available for oil to flow through a particular valve. Directional control
valves (DCV’s) are primarily available as one-way, two-way, three-way,
and four-way types.
In addition to classifying valves by the number of ways, a valve can
also be classified by the number of positions to which it can be adjusted.
A position determines which ports are connected to each other. Industrial
DCV’s are most often supplied as either 2-position or 3-position types.
The type we will explore in this LAP is a 3-position type.
The schematic symbols for directional control valves use what is
called a flow envelope to show the state of the flow paths for each valve
spool position. These flow paths can be shown as either opened or closed
by the envelope, as shown in figure 49.
NOTE
In the fluidpower industry, the terms opened and closed mean
just the opposite of the meaning in the electrical industry. An
electrical switch passes electricity when it is closed. A fluidpower
valve passes fluid when it is open.
OPEN (PASSING)
CLOSED (NOT PASSING)
Figure 49. Directional Control Valve Flow Envelopes
59
The flow envelopes shown in figure 49 represent one flow condition
each of a 2-way DCV symbol. A complete 2-position, 2-way DCV
symbol combines these two flow envelopes, as shown in figure 50. In
one spool position, the valve passes flow between its two ports. In the
other position, the ports are blocked.
To determine when the spool is in a particular position, operators are
placed next to each envelope. In figure 50, a spring is placed next to the
passing flow envelope. This means that the de-energized flow condition
is passing. The lever operator next to the blocked flow envelope shows
the flow condition when the lever is operated (valve is energized). In this
case, it is a blocked condition.
The complete description of the symbol shown in figure 50 is a
manually-operated, spring return, 2-position, 2-way DCV, normally open.
LEVER
A
SPRING
P
Figure 50. 2-Position, 2-Way DCV Symbol
A 4-way DCV symbol has two flow paths per envelope which show
the connections between its four ports (P, T, A and B). If the valve has
two positions, two flow envelopes are drawn side-by-side, as shown in
figure 51.
Each envelope shows the flow path condition for a particular
position of the spool. The flow path conditions shown in the DCV
symbol of figure 51 are called straight arrows and crossed arrows.
SPRING
STRAIGHT
ARROWS
CONDITION
A
B
P
T
CROSSED
ARROWS
CONDITION
ELECTRICAL
OPERATOR
Figure 51. 4-Way, 2-Position DCV Schematic Symbol
60
Figure 52 shows the condition of the 4-way DCV when its electrical
operator is energized. The spool moves to the crossed arrows condition
causing oil to flow from Port P to Port B and retract the cylinder. When
the electrical operator is de-energized, the spring pushes the spool to the
straight arrows condition causing the cylinder to extend.
SPRING
A
B
P
T
ENERGIZED FLOW
PATH CONDITION
ELECTRICAL
OPERATOR
ENERGIZED
Figure 52. 4-Way, 2-Position DCV Energized
The schematic symbol for a 3-position valve adds one more flow
envelope and a second spring, as shown in figure 53. The details of the
operation will be explained further in the skill.
A
B
P
T
Figure 53. 4-Way, 3-Position DCV Schematic Symbol
61
Activity 4. Flow Paths of a 3-Position, 4-Way Directional Control
Valve
Procedure Overview
In this procedure, you will determine the flow paths of a
3-position, 4-way directional control valve for each of its
positions. This activity will help you better see how this
valve works.
❑ 1. Obtain the open-end fitting from the loose items of the 850 Series
trainer.
When inserted into a hose end quick-connect, as shown in figure
54, this fitting opens the end of the hose.
Figure 54. Hose End with Open-End Quick-Connect Fitting
62
❑ 2. Set up the hydraulic circuit shown in figure 55, inserting the
open-end fitting into the hose end from Port A of the DCV.
This circuit will be used to determine the flow paths of the DCV in
each of its three lever positions.
When the DCV’s lever is shifted in one direction, Port P will be
connected to Port B, causing oil to flow through the flow meter.
When the DCV’s lever is shifted in the other direction, Port P will
be connected to Port A, causing oil to flow back to the reservoir
through the open-end fitting.
GAUGE A
GAUGE B
FLOW
METER
GAUGE C
SUPPLY
MANIFOLD
PRESSURE REDUCING
VALVE
RELIEF \ SEQUENCE
VALVE
1
1
2
2
3
3
NEEDLE
VALVE
A
B
RETURN
MANIFOLD
IN
D.C.V.
#1
CHECK VALVE #1
A
B
OUT
OPEN-END
FITTINGS
B
A
CHECK VALVE #2
B
A
Figure 55. Pictorial of a Circuit to Determine Directional Control Valve
Flow Connections
63
❑ 3. Now look at figure 56. This shows the same circuit as shown in
figure 55, except standard symbols were used for the components
instead of pictures. Compare the items shown to become more
familiar with the symbols used in hydraulics.
DIRECTIONAL
CONTROL VALVE
SUPPLY
MANIFOLD
A
B
IN
A
OUT
B
SHUTOFF
VALVE
RETURN
MANIFOLD
FLOW
METER
OPEN-END
FITTING
Figure 56. Schematic Diagram of a Circuit for Determining Directional
Control Valve Flow Paths
64
❑ 4. Close the needle valve.
❑ 5. Remove the cap of the filler/breather located on top of the power
unit tank and place the opened end of the hose into the
filter/breather opening.
Figure 57. Using the Open End Fitting to View Flow Returning to
Reservoir Through the Filler/Breather Opening
❑ 7.
❑ 8.
❑ 9.
❑ 10.
power unit.
B. Press the stop pushbutton on the motor starter to make sure the
starter is in the off position.
C. Plug in the power cord to a 115 VAC wall outlet.
CCW fully).
Turn on the power unit, increase the relief valve setting to 300
psi/2070 kPa and open the shutoff valve.
Open the needle valve 1/4 turn.
With the handle of the DCV remaining in the middle (center)
position, observe from which hose the oil flows.
No flow should be observed from either hose because the IN port
of this DCV is not connected to either hose when the lever is in the
mid position.
Pull out on the lever of the DCV and observe from which port the
oil flows. Record the letter of the port below.
Lever pulled out: IN port connected to ___________________port
You should observe flow through the flowmeter. This indicates
that the IN port is connected to Port B of the valve.
65
❑ 11. Now push in on the lever and observe from which port the oil
flows. Record the letter of the port below.
Lever pushed in: IN port connected to____________________port
❑ 12.
❑ 13.
❑ 14.
❑ 15.
❑ 16.
This time, fluid will flow from the open-end hose into the
reservoir. This indicates that the IN port is connected to Port A of
the valve.
Reduce the relief valve setting to minimum and turn off the power
unit.
Disconnect the hose from the IN port and reconnect it to the OUT
port.
This will allow you to now test the flow paths for the OUT port in
the three lever positions.
Turn on the power unit and increase the relief valve setting until
the pressure at Gauge S reads 300 psi/2070 kPa.
With the handle of the DCV remaining in the middle (center)
position, observe from which hose the oil flows. Again, no flow
should be observed from either hose, because the OUT port is not
connected to either hose when the lever is in the mid position.
Pull out on the lever of the DCV and observe from which port the
oil flows. Record the letter of the port below.
Lever pulled out: OUT port connected to _________________port
You should observe flow from the opposite port of that determined
in step 10, because when the IN port is connected to one of the
cylinder ports of a 4-way DCV, the OUT port is connected to the
other cylinder port.
❑ 17. Now push in on the lever and observe from which port the oil
flows.
Lever pushed in: OUT port connected to__________________port
❑ 18. Release the lever.
❑ 19. Reduce the relief valve setting to minimum and turn off the power
❑ 20.
❑ 21.
❑ 22.
❑ 23.
unit.
Close the shutoff valve.
Using a clean rag to catch any oil drops from the hose ends,
remove the hoses from the filler/breather opening, and replace the
cap on the power unit tank.
Remove the open-end fittings from the hoses and store with the
other loose items of the 850 Series trainer.
Now disconnect and store the hoses.
66
SKILL 6
CONNECT AND OPERATE A DOUBLE-ACTING HYDRAULIC
CYLINDER USING A 3-POSITION, MANUALLY-OPERATED DCV
Procedure Overview
In this procedure, you will set up a basic hydraulic
circuit to reciprocate a cylinder using a 4-way, 3-position
directional control valve. You will find that this method is
much easier than switching hose connections as you did in
an earlier skill.
❑ 1. Set up the hydraulic circuit shown in figure 58 on the 850 Series
hydraulic trainer.
NOTE
Make sure all your hose connections are firmly made.
GAUGE A
GAUGE B
FLOW
METER
GAUGE C
SUPPLY
MANIFOLD
RELIEF \ SEQUENCE
VALVE
CYLINDER
PRESSURE REDUCING
VALVE
1
1
2
FLOW
FLOW
CONTROL CONTROL
#1
#2
A
A
2
3
3
NEEDLE
VALVE
B
A
B
MOTOR
B
RETURN
MANIFOLD
IN
D.C.V.
#1
CHECK VALVE #1
A
CYLINDER
B
OUT
B
A
CHECK VALVE #2
B
A
Figure 58. Pictorial of a Basic Hydraulic Circuit
67
❑ 2. Now look at the schematic diagram shown in figure 59. Compare
this with the actual hose connections shown in figure 58.
As you can see, the hose connections are drawn to the center flow
envelope, which is the normal condition. The normal position of a
3-position valve is almost always designed to be the center
condition because the two springs center the spool.
NOTE
A 4-way DCV is the type needed to extend and retract a
double-acting cylinder. A 4-way DCV with 3-positions is used if
the cylinder must stop in mid-position.
NORMAL
CONDITION
FROM
PUMP
A
B
IN
OUT
TO
RESERVOIR
Figure 59. Schematic Diagram of Circuit Setup
❑ 3. Perform the following checkout procedures for the power unit.
in the Off position.
CCW fully).
❑ 4. Turn on the hydraulic power unit.
❑ 5. Open the shutoff valve.
68
❑ 6. Increase the pressure setting of the relief valve on the hydraulic
power unit to 200 psi/1380 kPa.
Since Gauge C is connected to the pressure manifold, it should
now be reading approximately the same as system pressure.
Record below the readings of Gauges C and S.
Gauge C = _____________________________________(psi/kPa)
Gauge S =_________________(psi/kPa) (on hydraulic power unit)
Also, you should observe that the cylinder does not move, even
though pressure has been raised. To understand why, look at the
diagram in figure 60.
With the manual lever on this DCV in the mid-position, the
springs hold the valve spool in the center position. This causes the
spool’s lands to block flow at all ports and hold the actuator
stopped.
Because the flow is blocked by the valve the pressure in the supply
line builds up and the relief valve opens to dump the oil flow back
to tank.
CYLINDER STOPPED
LEVER
HANDLE
IN MID
POSITION
B
A
P
T
BLOCKED
HIGH
PRESSURE
RELIEF
VALVE
LOW
PRESSURE
RESERVOIR
Figure 60. DCV with Spool in the Mid-Position
69
❑ 7. Now test your hydraulic circuit by pushing in on the lever of the
DCV. This will cause the cylinder’s rod to extend. Continue
holding the lever until the cylinder’s rod is fully extended. Then
release it.
When the manual lever is placed (pushed) in toward the body, the
spool is shifted to connect Port P with Port A, and Port B with Port
T. This is the “straight arrows” position. Flow through the valve is
P to A, and B to T, as shown in figures 61 and 62. This causes the
actuator shown to extend.
CYLINDER EXTENDING
LEVER
HANDLE
PUSHED IN
A
OPEN TO
PORT T
B
P
T
OPEN TO
PORT A
RELIEF
VALVE
RESERVOIR
Figure 61. Pictorial of DCV Shifted to Straight Arrows Condition
70
CYLINDER
EXTENDS
A
IN
B
OUT
FROM
PUMP
TO
RESERVOIR
Figure 62. Schematic of DCV Shifted to Straight Arrows Condition
❑ 8. Retract the cylinder by pulling out on the lever of the directional
control valve. Continue holding the lever until the cylinder’s rod is
fully retracted.
When the lever is placed (pulled) away from the body, the spool
shifts to connect Port P with Port B, and Port A with Port T, as
shown in figures 63 and 64. This is called the crossed arrows
condition and causes the actuator to retract.
CYLINDER RETRACTING
CONNECTED
TO PORT
T
LEVER
HANDLE
PULLED
OUT
A
CONNECTED TO
PORT B
B
P
T
RELIEF
VALVE
PUMP
RESERVOIR
Figure 63. Pictorial of DCV with Spool Shifted to Crossed Arrows Condition
71
CYLINDER
RETRACTS
FROM
PUMP
A
B
IN
OUT
TO
RESERVOIR
Figure 64. Schematic of DCV with Spool Shifted to Crossed Arrows
Condition
❑ 9. Repeat steps 7 and 8 several times to cycle the cylinder. During
one of the cycles, release the lever while the cylinder’s rod is
extending and in midstroke. What happens? Does the cylinder stop
or does the rod keep moving?
_____________________________________________________
_____________________________________________________
You should observe that the cylinder stops in mid-stroke because the
spool goes to the center position and blocks the ports. This is one of
the functions for which you should choose a 3-position valve.
NOTE
3-position valves are made with center conditions other than
the blocked center condition. You will learn more about the other
center conditions in a later LAP.
❑ 10. Reduce the relief valve setting to minimum.
❑ 11. Turn off the power unit.
❑ 12. Move the handle of the DCV back and forth to remove any
pressure in the circuit.
❑ 13. Switch the two hoses connected to the ports of the cylinder with
each other so that the cap end is connected to Port B of the DCV
and the rod end is connected to Port A.
❑ 14. Turn on the power unit and increase the relief valve pressure
setting to 200 psi/1380 kPa.
❑ 15. Cycle the cylinder again by operating the DCV. What difference
do you observe in how the system operates?
_____________________________________________________
_____________________________________________________
72
You should observe that the cylinder moves in the opposite direction
when the lever is pushed in. This step shows that the direction of the
cylinder’s motion depends not only on the internal porting of the DCV
but also how the DCV and cylinder are connected. The cylinder motion
can easily be changed by switching hoses. This is a common task
performed in industry.
❑ 18. Move the handle of the DCV back and forth to remove any
pressure in the circuit.
SKILL 7
DESIGN A DUAL CYLINDER HYDRAULIC CIRCUIT
Procedure Overview
In this procedure, you will further develop your
understanding of hydraulic circuits by designing a basic
circuit.
❑ 1. Read the following scenario.
Scenario: Your company has asked you to design a hydraulic
shearing press that will cut off steel sheet stock. This shearing
press could use just one cylinder to operate but you have decided
that two cylinders would be better in order to maintain a more even
force on both sides of the shear.
CYLINDER
2
CYLINDER
1
Figure 65. Hydraulic Shearing Press
73
❑ 2. Your task is to design a hydraulic circuit that will cause the
cylinders to extend and retract using a single directional control
valve. The valve should provide extend, retract, and mid-position
stop capability.
Draw the circuit schematic using the symbols you have learned in
this LAP. Start your drawing from the manifolds, as shown in
figure 66. Remember that the circuit symbols are drawn in the
de-energized condition.
SUPPLY
MANIFOLD
CYL
1
RETURN
MANIFOLD
CYL
2
SHEAR
Figure 66. Schematic of Circuit Design
❑ 3. Now add pressure gauges to your design to measure the system
pressure and the pressures at the cap and rod ends of the cylinder.
74
SEGMENT 4
SELF REVIEW
1. The actuator that produces linear motion is called a(n)
____________.
2. The number of ways that a directional control valve has
defines the number of _______ paths for the fluid to travel
through the valve.
3. Applications use 3-position, 4-way DCVs to provide
3-function control of the cylinder: extend, retract, and
________.
4. The lever is just one type of ________ method of moving
the spool from one position to the other.
5. Double-acting cylinder direction can be reversed by
switching the hose connections at the ________ or at the
________.
6. The type of cylinder that needs to be powered in both
directions is called a(n) _____________ cylinder.
7. The spool of a 3-position DCV is held in the middle position
by the ___________________.
8. A cylinder rod moves when the _________ against the
piston reaches a point that can no longer be resisted by the
piston.
9. The crossed arrows DCV condition causes Port P to connect
to Port ________.
10. A schematic is usually drawn with connections drawn to the
__________ condition flow envelope of the DCV.
75

basic hydraulics - Oakland High School

Transcription

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