Hydra-Cell pumps are a type of sealless, positive
displacement pump, using a hydraulically balanced diaphragm as the displacement
mechanism. As such, Hydra-Cell pumps do not have a dynamic seal interface
which plunger and piston style positive displacement pumps have and thus are
more reliable, especially for difficult to pump fluids. The simplified
design of Hydra-Cell pumps also simplifies troubleshooting.
New Hydra-Cell Pumps
If you are not receiving the pressure/flow desired, the
likelihood that you have a system issue is very high because Hydra-Cell pumps
are tested at full flow rate and pressure prior to shipment. Unlike other
manufacturers, which test only a percentage of their products, 100% of
Hydra-Cell pumps are tested prior to shipment so you can be confident it was
working when it was shipped.
In my experience, most flow rate issues are related
to the inlet side of a system. You need to ensure that there is sufficient
fluid available to support the desired flow rate. Even though Hydra-Cells
have some suction lift capabilities and will self-prime, insufficient NPSHa will
starve the pump of adequate fluid resulting in cavitation. Simply put,
trying to displace more fluid than available results in a vacuum condition
allowing the liquid to change to its vapor phase; this violent phase change
results in rough running (flow/pressure) and operating this way for prolonged
periods can damage the check valves.
A way to check if this is an issue is to
slow the pump speed down to see if the pumping action becomes smoother and
quieter. If it does, it is confirmation of inadequate NPSHa.
start-up as expected but begin to operate roughly after a period of time might
be symptomatic of clogged filtration, aeration of fluid due to a high percentage
of recirculation or a change in the head pressure available as the feed tank
volume decreases (lack of NPSHa).
Newer pump systems which initially worked well,
but then sat idle for months will sometimes have “stuck” internal check valves
due to residual fluid remaining within the pump which dried out or otherwise
left a sticky residue. A pressurized inlet, such as city water pressure,
can free-up sticky valves.
On the discharge side of a new pump system, make sure
that your pressure-regulating valve is set properly. Generally you should
set the pressure regulating valve to the maximum allowable pressure you wish to
operate at after the pump has primed itself and if you are not receiving the
desired pressure, is there fluid being bypassed? Since pressure is a
function of flow rate, there needs to be adequate restriction, so bypasses, leaks
and oversized/worn spray nozzles are factors to consider.
Existing Hydra-Cell Pumps
Pumps which have a history of performing
satisfactorily are often easier to troubleshoot because rough running is
typically related to worn check valves. The check valves within the pump
head can cycle up to 29 times per second when operated at 1750 RPM, so
eventually the interface of the valve and seat wears. Worn check valves
reduce sealing efficiency and the flow rate decreases as a result. This is
especially noticeable when pumping at elevated pressures. Check valves are
easy to replace and are offered in many materials to maximize both chemical
resistance and abrasive wear.
Hydra-Cell pump elastomers (o-rings and diaphragms)
are not typically wear items; whereas you can predict check valve wear with some
success, o-rings and diaphragms do not exhibit that type of wear. Chemical
and temperature incompatibility can degrade these elastomers but when that is
not an issue, o-rings and diaphragms last years. Many customers elect to
replace the elastomers when they replace their check valves because it does not
add much to the overhaul kit cost and the pump head is already opened to replace
the check valves, so it is a prudent, proactive approach to pump maintenance.