How to Prolong the Life of Your Gas Chlorinator

How to Prolong the Life of Your
Gas Chlorinator
The purpose of a chlorinator is to
meter and deliver a set feed rate of
chlorine gas from a chlorine cylinder
(Figure 1). To do this, gas
chlorinators must be operated and
maintained properly.
Direct Cylinder Mounting
A vacuum-operated gas chlorinator
reduces the gas pressure from a
chlorine cylinder to less than
atmospheric pressure and transports
the chlorine gas to the point of
application.
The easiest and safest way to make
the connection from a gas cylinder to
the chlorinator is by direct cylinder
mounting. In direct mounting, the
chlorinator inlet valve is attached
directly to the cylinder calve by a
positive metallic yoke connection
that is sealed by a single lead gasket.
This soft-lead gasket should be
changed every time the chlorinator is
disconnected.
After the chlorinator is placed on the
cylinder valve, the lead gasket
connection must be secured. One
common error is to over tighten the
lead gasket connection, which can
damage the yoke of the chlorinator
and, as a result of distortion, cause a
leak. It is necessary to tighten the
connection only one half to three
quarters of a turn after contact is
made with the lead gasket.
After the chlorinator is secured on the
cylinder valve, the valve should be
opened only one quarter of a turn so
it can be quickly closed in an
emergency.
Household ammonia vapor, applied
at the lead gasket seal, will indicate
chlorine leaks. Chlorine gas in the
presence of ammonia vapor
produces a cigarette-like smoke, a
visual indication of a chlorine leak. If
a leak exists, first check that the
packing on the chlorine cylinder
valve is tight. Second, check the lead
gasket; however, this connection is
usually tight.
CAUTION: If the stem of the chlorine
cylinder valve is difficult to open, do
not force it. Damage to this valve
could cause a chlorine leak. If the
valve is difficult to open, it is much
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better to return the cylinder to the
chlorine supplier, eliminating the risk
of a gas leak caused by a broken
valve. It is the supplier’s
responsibility to provide valves in
good condition. Also, when the valve
is open, the cylinder wrench should
remain on the valve. This provides
for a quick shut-off (one-quarter turn)
of the chlorine source. A label should
be provided beneath the cylinder
wrench, but on top of the valve,
showing the direction in which the
valve should close. If such a label is
not posted, this could cause a valve
to be turned in the wrong direction,
thus opening, rather than closing, the
valve. All chlorine valves are fitted
with right-hand threads.
Figure 1 - Schematic of Direct Mounted Gas Chllorinator
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Interconnection Manifold
Direct mounting is by far the safest
and most convenient way to mount a
chlorinator to a cylinder, but is it is
not always possible. If several
cylinders are used to provide
chlorine, then an interconnection
manifold is necessary.
The following three items are needed
to make an interconnection manifold:
the chlorine gas manifold - made
of seamless steel pipe with a
chlorine valve for chlorinator
mounting,
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a flexible connector (from the rigid
pipe manifold to the chlorine
source) - made of cadmiumplated copper. This provides a
flexible line between the manifold
and the chlorine cylinder,
an isolation valve - made of
bronze and located between the
flexible connector and the cylinder
valve.
If the gas is maintained in a dry
condition from the gas cylinder to the
chlorinator, very little, if any,
corrosion will result. When a chlorine
pressure connection is broken,
chlorine is exposed to the moisture in
the atmosphere. This allows some
moisture to combine with the chlorine
gas. If moist air collects in the
manifold, acids are formed and
corrosion will occur that may cause
the manifold to fail.
The purpose of the isolation valve is
to isolate the manifold from
atmospheric moisture. The isolation
valve is merely a valve equipped
with an adaptor that is connected
directly to the chlorine gas cylinder.
Before the connection is broken, the
isolating valve is closed and the
chlorine gas cylinder valve is closed.
Therefore, when the connection is
broken, only a very limited amount of
moisture will be allowed to enter the
system.
When a new container is connected
and the connection is replaced, the
isolating valve and the chlorine gas
cylinder valve can be reopened. The
use of an isolating valve can easily
double the life of a chlorine gas
manifold.
The Ejector: Heart of the
Chlorinator
To understand chlorinator operation,
consider the ejector the heart of the
system. The ejector contains a
100.9050.0
venturi nozzle that creates a
vacuum. Water pressure is supplied
to this nozzle by a pump, and the
differential pressure across the
nozzle creates a vacuum.
The vacuum then moves through a
check-valve assembly, usually part of
the ejector body itself, then through
tubing to a rate valve, which controls
the rate of feed of the chlorine gas.
The vacuum level is reduced across
the rate valve to a lesser magnitude
at the diaphragm assembly of the
vacuum regulator.
The diaphragm assembly is
connected directly to the inlet valve
of the vacuum regulator, which has
gas under pressure on one side and
a vacuum on the other. The vacuum
on one side of the diaphragm is
about 20 inches (508 mm) of water
column. The other side of the
diaphragm is open to atmospheric
pressure.
This differential pressure causes the
diaphragm to open the chlorine inlet
valve (which has chlorine gas
pressure on one side of it), allowing
the gas to move, under vacuum,
from the chlorine source, past the
diaphragm, thought the chlorine
flowmeter, past the rate valve,
through the tubing, past the checkvalve assembly, into the nozzle area,
and then into the water at the point of
application. See Figure 1.
It is most important to realize that
chlorine is being drawn from the
chlorine cylinder to the water via the
vacuum created in the ejector. If the
ejector is not functioning, the
chlorinator will not operate. The vast
majority of problems that occur in
chlorination equipment can be traced
to the ejector.
Measuring Water Pressure
A good service tool is a pressure
gauge located just before the water
inlet of the ejector. This gives a
measurement of the water pressure
that is available to the ejector.
Measuring water pressure
downstream of the ejector is
somewhat more difficult, because the
chlorine solution is corrosive.
Downstream pressure is that which
exists at a given installation as back
pressure.
Back pressure can be defined as a
combination of the static pressure
against which the chlorine solution
must be injected, plus the pressure
due to friction losses in the solution
line. Both of these pressure must be
considered because insufficient
sizing of the chlorine solution line can
amount to a considerable increase in
back pressure, which may reduce the
differential pressure across the
ejector to such a point that the
chlorinator will not operate.
Various tools supplied by chlorinator
manufacturers measure back
pressure. A temporary gauge can be
installed if there is some doubt
whether an adequate pressure
differential exists.
Check-Valve Assembly
Assuming the pressure differential is
proper and the water flow through the
ejector is adequate, the check-valve
assembly, which is usually part of the
ejector, is an area of concern. The
check-valve assembly prevents
water from entering the vacuum
regulator portion of the chlorinator.
If chlorine solution is injected in the
presence of any positive pressure
when the water flow through the
ejector is stopped, a vacuum will no
longer exist in the ejector. A positive
pressure, equal to the static head
into which the chlorine solution is
injected, will exist. This positive
pressure will exist at the check-valve
assembly.
If there is no check-valve assembly,
the water will be forced into the
vacuum regulator portion of the
chlorinator.
Check valve failure. Failure of the
check valve is usually indicated by
some quantity of water in the chlorine
gas metering tube.
The check-valve may fail for a
number of reasons, the most
common of which is an accumulation
of deposits on the seat of the check
valve. This means that even though
the check-valve closes, it is blocked
and not completely sealed, allowing
water to pass through to the vacuum
regulator.
The second most common failure,
depending on how frequently the
check valve is cycled, occurs when
the check-valve seat material
becomes distorted. This is most
common on systems, such as a deep
well, where the pressure against the
ejector and the number of cycles
during a day are fairly high.
Most chlorinator manufacturers offer
several check-valve arrangements,
depending on the pressure that the
ejector is subjected to when the
chlorinator is shut off. Generally, as
the pressure increases, the stiffness
of the diaphragm and the hardness of
the check-valve seat increase.
The check-valve is usually identified
by the manufacturer with a mark on
the ejector body itself. Consult the
chlorinator manufacturer to
determine of the proper check-valve
is installed.
Removing Water From the
Chlorinator
If water pressure builds in the
vacuum regulator, the diaphragm
assembly will move in the opposite
direction of the chlorine inlet valve,
and water will be allowed to vent to
the atmosphere in the same way as
when excess gas pressure builds in
the chlorinator.
Depending on the capacity of the
chlorinator, it may be a simple
operation to remove the water. If only
a small amount of water enters the
chlorinator and the check-valve
problem is remedied, the chlorinator
can be restarted and the water will be
drawn out with the chlorine gas.
It may be difficult to remove the
water from low capacity units (less
than 10 PPD/4.5 kg/h) because the
quantity of gas drawn through the
chlorinator is very small.
To safely remove the water from
small capacity chlorinators, remove
the vacuum regulator from the
chlorine cylinder source and allow
the chlorinator to pull in air rather
than chlorine. This will allow the
chlorinator dry out so it can be
reinstalled on the chlorine cylinder
source.
Where the metering tube is small,
the liquid can cause the metering ball
to stick. When this happens, it may
be necessary to disassemble the
chlorine flowmeter and manually dry
it before the chlorine is returned to
operation.
When the check-valve fails, it
sometimes becomes so distorted that
it blocks the passage of vacuum and
it appears as though no vacuum is
present. If the ejector is operating
properly, suction exists at the
vacuum port and gas will flow.
The Chlorinator’s Vacuum
Integrity
The remainder of problems
associated with chlorinator are
related to vacuum integrity. The
chlorinator must be vacuum-tight
from the ejector or the vacuum
regulator inlet valve for a flow of gas
to exist. There are three significant
situations that can occur if there is a
break in vacuum.
No indication appears on the
flowmeter, even though vacuum is
being created. This indicates a
vacuum leak at the top of the meter
tube or somewhere downstream
toward the ejector from this point.
If the leak occurs above the float,
this indicates the O-rings on the rate
valve stem are not sealing. If the
gasket on the top of the meter tube is
not sealing, it has probable been
caused by someone grasping the
vacuum regulator by the meter tube
when changing cylinders, thus
dislodging it from its sealed position.
When confronted with this situation,
check all vacuum tubing and
connections, the rate valve O-rings,
and the gasket on top of the
flowmeter for vacuum leaks.
O-rings are used in most chlorinator
to provide a seal between two parts.
In the case of the rate valve, the Orings slide as the rate valve is
moved.
Although chlorinators are constructed
of materials designed to withstand
the effects of chlorine gas, even the
most substantial O-rings eventually
become brittle, and can actually
remove themselves in the constant
adjustment of the gas flow. They may
disintegrate and be fed out through
the vacuum tubing.
When this happens, there will be a
loss of vacuum through the rate
valve. (Most chlorinator
manufacturers provide spare parts
kits, including O-rings, with their
chlorinators).
A vacuum leak somewhere below
the float in the metering tube. This
can be caused by a leak at the
bottom metering tube gasket. In this
case, the flowmeter will indicate a
flow, but the flow will be air, not
chlorine gas. If any connection below
the bottom metering tube gasket
leaks, air will register as gas flow in
the flowmeter.
The ejector is located at the
chlorine application point. In the
past, it was common practice to
mount the ejector and vacuum
regulator inside a cabinet. But for
safety and economy, the ejector
should be located exactly where the
chlorine is to be applied. This
eliminates pumping the chlorine
solution to the point of application,
which may be several hundred feet.
By placing the ejector at the point of
application, a break in the vacuum
tubing will cause the chlorinator to
shut off immediately, stopping gas
flow or damage from chlorine
solution lead,
With a cabinet mounted ejector, a
broken solution line to the application
point could allow corrosive chlorine
solution to contaminate the area.
There are other advantages to
placing the ejector as close as
possible to the point of application.
For example, this arrangement
eliminates the back pressure
resulting from friction losses in very
long solution lines. When the
vacuum regulator portion of the
chlorinator is mounted directly at the
chlorine source, gas pressure lines
and the accompanying problems are
eliminated. The gas is conducted
under vacuum to the point of
application, minimizing the hazards
of pressurized chlorine gas and
solution piping.
However, the most practical
configurations of equipment are not
always possible. If solution lines are
unavoidable, they should be routed
to an area where a break will not
cause damage. Also, valves within a
solution line should be of the onequarter turn, PVC variety because
these will cause the fewest
maintenance problems and produce
the lowest friction loss.
Reprinted from an article published in
Opflow, a publication of the
American Water Works Association,
July 1991, by Jesse Wolf, Technical
Services Manager, Capital Controls
Company, Inc.
100.9050.0
Design improvements may be made without notice.
Represented by:
CAPITAL CONTROLS
Severn Trent Services
3000 Advance Lane Colmar, PA 18915
Tel: 215-997-4000 • Fax: 215-997-4062
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