Service Manual 73
Page 31 of 32
2. Problem: Capacity is too low.
a. Air leaks in suction line.
b. Suction losses are too high. The suction lift is too great or the suction line is too small or
too long. This can be detected by installing a vacuum gauge directly at the pump suction.
The maximum vacuum at the pump suction should never exceed 15” of mercury.
Vaporization caused by higher vacuums will generally result in capacity drop off.
Redesign suction conditions.
c. Pump speed is too slow.
d. Strainer too small or obstructed.
e. Suction pipe or port not immersed in liquid deep enough
f.
Piping improperly installed permitting air pocket to form in the pump.
g. Increased clearances or wear in the pump will sometimes cause the pump to deliver an
insufficient supply of liquid. This may be corrected by reducing the thickness of the cover
gaskets. A folded gasket or a slight amount of dirt can exaggerate the problem and
cause leakage. Refer to Assembly Procedure section for minimum end clearances.
3. Problem: Pump works spasmodically.
a. Leaky suction lines.
b. Suction conditions vary.
c. Air or vapor in liquid.
4. Problem: Excessive power draw.
a. Pressure too high.
b. Liquid more viscous than originally expected.
c. Suction or discharge lines obstructed.
d. Insufficient horsepower.
e. Mechanical defects:
i.
Drive shaft and pump are misaligned.
ii.
Pump is binding due to insufficient end clearance.
iii.
Pump shaft is bent.
iv.
Misalignment within pump due to bad piping or poor installation, causing strain or
distortion.
