M Ball-valve concrete pumps Long used for low- volume pumping,

Ball-valve concrete pumps
Long used for lowvolume pumping,
now some are taking on
more demanding jobs
BY FRANCIS C. WILSON
CONSULTANT
WAUKESHA, WISCONSIN
ore ball-valve pumps
are in use than any other kind of concrete
pump. Most are lowvolume units with output capacities less than 30 cubic yards per
hour. Although the small models
are often called grout pumps, many
can be used for structural concrete
and shotcreting where low-volume
output is suitable. They’re used for
repairing underwater concrete, filling fabric forms, placing concrete
in heavily reinforced sections, and
building bond beams for masonry
walls. Some hydraulically dri ve n
models have pumped stru c t u ra l
concrete at outputs exceeding 150
cubic yards per hour.
M
A ball valve is actuated entirely by flow of the concrete. On the intake cycle
(above), ball movement at the feed hopper is limited by bars or an off-center
cam. On the discharge cycle (below), concrete flow seats the ball. The ball at
the discharge cylinder seats during intake and opens during discharge.
How the ball valve works
Operation of the ball valve is simple (see figure). The valve is actuated entirely by flow of the concrete,
reversing swiftly with the flow. No
springs or actuators are needed. If
on one cycle the ball doesn’t seat
fully, the flow tends to take out any
obstruction that isn’t oversize and
the valve returns to full function.
Some models permit controlling the
ball movement with off-center cams
or bent bars. Adjustments can be
made while the unit is running.
The balls themselves last for long
periods and are changed easily.
Balls with differing weights are used
for pumping concretes with differing unit weights—lightweight, cellular, heavyweight, and normalweight concrete. The same ball seat
is used for all ball weights and can
be replaced easily.
There isn’t enough force from
concrete flow pressure against the
ball to push larger rock mixes out of
the path from the ball to the seat.
Because of this, most ball-valve
pumps can’t pump concrete with
aggregate larger than pea gravel size
(100% passing the 1⁄2-inch sieve, also
called l⁄2-inch minus material). Don’t
confuse this with aggregates having
a nominal maximum size of l⁄2-inch
(ASTM Size No. 7) which can have as
much as 10% passing the 3⁄4-inch and
retained on the l⁄2-inch sieve. These
oversize particles may prevent the
valve from seating.
Drive mechanisms for
ball-valve pumps
Many ball-valve rigs are mechanically driven. These have one concrete pumping piston driven off a
series of belts, chains, and a crank.
The resulting uneven output rate is
leveled out to more uniform flow by
a second compensating piston driven with a cam or heavy spring. The
unit works well with sand grout mixes and with mixes having up to
about 30% aggregate under l⁄2 inch.
Hydraulic-drive ball-valve pumps
use a two-cylinder hydraulic drive
much like those on larg e - ro c k
pumps. These pump models require
a junction pipe or siamese just as
h a rd rock pumps do. The shear face
at the junction creates considerable
flow resistance, but not much
greater than that developed around
the flow compensator in mechanical pumps.
With large-diameter (4 to 6 inches) hydraulic cylinders and long
strokes (24 to 42 inches), flow in a
h yd raulic ball-valve pump doesn’t
pulse as often as flow in a mechanical pump. The resulting smoother
flow is especially useful in wet shotcreting. Another benefit of longer
strokes is fewer valve actuations,
and thus less valve wear.
Hyd ra u l i c - d ri ve pumps can
pump concrete at a faster rate and
at higher pressures than mechanical
pumps, permitting concrete to be
pumped higher and further. When
a jam from oversize or foreign materials begins to form, ball-valve
pumps with self-regulating oil
pumps swiftly sense the obstruction
buildup, reduce oil flow, and increase oil pressure to usually cause
the jam to pass through.
Pumplines
Because the maximum aggregate
size doesn’t exceed l⁄2 inch and highvolume output isn’t needed, smalldiameter delivery line and hose are
commonly used for ball-valve
pumps. With an inside diameter of 2
or 21⁄2 inches and a low pressure rating, the hose cuts contractor labor
costs because it’s lighter and easier
to handle.
Depending on the drive mechanism, maximum concrete line pressures may range from 300 to 900 psi.
On most jobs 100 to 150 psi is all
that’s needed. For higher pressure
work such as forced grouting or
high-lift pumping, higher rated
(stronger) line and hose are needed.
For high-pressure work, lines, hoses,
and clamps also should be inspected frequently for damage.
On the parts of a job where it’s
feasible, steel slickline has seve ra l
advantages:
• Lower first cost
• Reduced pumping pressures
• Greater durability
For pumping concrete ve rt i c a l l y
more than 100 feet, use of slickline is
much preferred. The vertical lines
must be firmly supported by brackets or lashing, and bolt line couplings should be used, especially
where access is difficult. Latch
clamps are suitable for low-pressure
pumping but shouldn’t be used
where several sections of hose or
pipe are supported only by the
clamps. A falling pump line can
cause severe injuries.
Using the pump efficiently
Mixes with aggregates heavy in
the sand sizes require relatively high
water contents to make them workable. To get the needed strength, cement contents may range from 550
to 900 pounds per cubic yard. The
higher cement contents increase
cost, drying shrinkage, and heat
generation and also may make the
concrete sticky and hard to pump.
One commonly available solution is
to replace some of the cement with
fly ash. This reduces cement cost
and improves pumpability.
Concretes made with crushed
stone and stone sand are hard if not
impossible to pump. Blending in a
small amount of natural sand greatly improves pumpability. So does
mixing pea gravel (rounded particles) with crushed stone.
Most sands are suitable for
pumped concrete but dredge sands
typically lack fines. Pumpability is
improved by adding as little as 30
pounds of crusher dust, wash tailings, blow sand, or fly ash to a cubic
yard of the concrete. Almost any
gain in pumpability as a result of aggregate blending also improves concrete finishability, surface appearance, and strength.
Uniformity is the key word for
ball-valve pump mixes, just as it is
for mixes pumped by all rigs. Consistent concrete makes the pump
and the job run smoothly. For trouble-free operation, avoid oversize
aggregate particles, frost balls, clay
lumps, and random inclusions such
as tramp iron. Keep the hopper
grate in place. Also inspect and repair damaged hoses and lines that
might cause rock jams.
Pump safety
Ball-valve pumps have few safety
problems when concrete discharges
freely and the line isn’t exc e s s i ve l y
long. If there’s a line blockage, howe ve r, the line and couplings could
be subjected to excessive pressure
that can cause bursting. Ball va l ve s
operate as solid check valves and
special care is necessary to relieve
p re s s u re. Even during routine disconnections,such as after filling a
cavity, care must be taken. The pressure can be relieved safely by controlled, gradual opening of a coupling. Also, some machines have
either a surge chamber valve or a
long lever on the first coupling for
pressure dissipation.
Before buying a pump
A ball-valve pump has several advantages. First cost is low and there
are few wear parts. Because of its
simple design, the pump is easy to
clean and maintain. The units are
small and maneuverable, the hoses
easy to handle.
This pump is primarily limited by
pumping rate and aggregate size re-
strictions. Although hydraulic models have pumped at rates up to 150
cubic yards per hour, typical uses
are for jobs requiring no more than
30 yards per hour. The units can’t
pump 3⁄4-inch-aggregate concrete or
l a rg e r. Before buying a pump, consider what concrete you’ll usually be
pumping and what output volume
and pressures you’ll need.
Also check the availability of l⁄2inch minus aggregate in your area
before buying a pump. In some areas 1l⁄2-inch and 3⁄4-inch aggregates
are available for concrete to meet
state highway department specifications, but l⁄2-inch material may be
wasted or ground into sand. In such
a re a s, ball-valve pumps are limited
to pumping sand grout mixes.
For information about reliability,
ease of operation, and technical
backup from manufacturers, talk
with users of ball-valve pumps.
Learn what sort of jobs users do and
how their pumps have perf o rm e d .
Ask about the pump’s tolerance for
an occasional unfriendly mix. How
easy is it to clear blockages and to
clean the machine at day’s end?
What are the maintenance costs
and how much time is spent keeping the unit in operating condition?
Finally, how responsive is the manufacturer to requests for help in diagnosing problems? Studying manuf a c t u re r s’ literature and service
manuals can help you make a buying decision. But talk with users before choosing your pump.
PUBLICATION#C880145
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