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Catalog 207 • Page 167
TROUBLESHOOTING YOUR FLEXIBLE IMPELLER PUMP
Low flow: Reduced flow will occur when the impeller is damaged. Bowed, missing, worn or ripped
blades (see picture) will reduce flow. A worn cam, wearplate or cover plate will also reduce flow.
The replacement of these parts, when worn, normally cures the problem. Another cause of low
flow is an air leak. This can occur anywhere along the suction line, within the sea strainer, or
within the pump. Check all hoses, hose clamps, fittings, gaskets and the pump water seal.
Not priming: All of the causes of low flow described above can also prevent the pump from priming.
How to prevent impeller failure: The main causes of premature impeller failure involve running
the pump dry, with a restricted suction or with a blocked discharge. Confirm your inlet seacock
is in the open position before engine start. You would be surprised how often this simple step is
forgotten. Regularly clean your suction strainer and confirm all old impeller blades are removed
when replacing your impeller. These steps will reduce the majority of system flow restrictions.
FLEXIBLE IMPELLER
When To Replace Your Impeller
CENTRIFUGAL
TROUBLESHOOTING YOUR CENTRIFUGAL PUMP
Not priming (for self-priming models): Any air leak or blockage along the suction line will pre-
vent the pump from priming. Check your hose, hose clamps, fittings, and strainer. If your
suction line checks out, verify pump shaft rotation and impeller spacing (impeller spacing
within a self-priming centrifugal is critical). Self-priming centrifugals require liquid in their
housing to prime. If your pump has sat long enough for your liquid to evaporate, or your
pump was just installed, verify that your pump housing has been filled. Also, verify your shaft
rotation. A self-priming centrifugal pump will not prime when run in reverse.
Low flow: The most common reason for centrifugal pumps to experience low flow upon initial
start up is reverse rotation. A centrifugal pump will deliver approximately 60% of their designed
flow when rotated backwards. An air leak along the suction or line blockage anywhere in the
system will reduce flow. Clear all lines, test for leaks, and verify your chosen line size, fittings
and valves are not overly restricting your flow.
How to prevent premature seal failure: The typical mechanical seal is designed to last thousands of
hours. The common causes of premature seal failure include running the pump dry (closed seacock
or blocked suction), cavitation (restricting the inlet flow to the pump by reduced line size, clogged
strainer or partially blocked or collapsed suction line), thermal shock (a quick change in tempera-
ture that shatters the ceramic element of the seal, and often occurs when a pump has been run-
ning dry long enough to heat up the seal significantly before fluid is allowed to enter the pump),
and deadheading (running the pump with a closed discharge for extended periods of time).
TROUBLESHOOTING YOUR DEMAND STYLE DIAPHRAGM PUMP
Not priming: Any air leak or blockage along the suction line will prevent the pump from priming.
Check your hose, hose clamps, fittings, and strainer. If your suction line checks out, the cause
usually centers on a problem with the valves. Open up your pump and verify the valve o-ring is
in place and there is not any debris clogging the valves. Valves occasionally swell or lose their
resilience. This type of valve damage is not always visible. Luckily valves are relatively inex-
pensive and easy to replace.
Low pressure or automatic switch not shutting off: Slight swelling of the check valves is the
most common cause of low pressure or the pump not automatically shutting off. If after valve
replacement the problem persists, replace the pressure switch.
Leaking: A ripped or cracked diaphragm is normally the cause of liquid leaking out of the pump.
Additional damage to the bearings and motor can be avoided if you catch the leak early.
Pump does not respond to electrical power: Bypass the pressure switch by removing the two
wires attached to the switch and connect them momentarily together. If the pump turns over,
your pressure switch requires replacement. If your pump remains lifeless after bypassing the
switch, your motor needs replacement (some models have replaceable brushes).
PITTING
BEAD WORN
TO A FLAT
CAVITATION
TEAR
BOWED (SET)
RIPPED
VANE
GEAR
When To Repair Your Gear Pump
TROUBLESHOOTING YOUR GEAR PUMP
Not priming: Any air leak or blockage along the suction line will prevent the pump from
priming. Check your hose, hose clamps, fittings and strainer. Dry gears will also reduce the
pump’s ability to prime. Simply pour a small quantity of your liquid into the suction or dis-
charge of the pump and try again. If none of these ideas work, disassemble your pump to
inspect for wear as described in our picture. If excessive wear exists, you will need a rebuild
kit or complete pump head.
How to prevent premature pump failure: Gear pumps were designed to transfer or spray clean
liquids. The close tolerances between both gears and the pump body are the key to its ability
to deliver a strong suction and high discharge pressure. However, sand or debris will wear all
contacting surfaces or even lock up the pump potentially causing motor or shaft damage.
“DEMAND STYLE” DIAPHRAGM
Troubleshooting Your Pump
PRESSURE
SWITCH
O-RING
DIAPHRAGM
VALVE
What Cavitation (Low NPSH)
Will Do To Your Impeller
TROUBLESHOOTING