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Appendix F—Troubleshooting Guide
In diagnosing pump and system troubles, record the
following data during product transfers:
1. Pressure at pump suction.
2. Pressure at pump discharge.
3. Pressure in truck tank.
Problem
Cause
Low capacity
Pump speed too slow
High differential pressure
External bypass valve
stuck open or set too low
Clogged strainer
Suction pipe too small
or restricted
Worn vanes
Pump without vapor return
Worn sideplates
Vanes sticking
Pump runs
Valve closed
but no flow
Excess flow valve slugged
Broken shaft
Defective meter
Pump will not
Foreign matter in pump
turn–locked up
Vanes broken
Bearing seized
Moisture frozen in pump
Will not build
pressure
Poor suction conditions
External bypass valve
set too low
Worn vanes
and/or sideplates
4. Pressure in tank being filled.
5. Pipe size and length of suction and discharge lines.
6. Size and length of vapor equalizing line.
7. Pump speed if practical.
Solution
Check engine speed and PTO ratio. Consult pump performance
curve. Use tachometer on pump if speed is questionable.
Restriction in discharge piping or hose too small. Vapor
equalization lines too small or not used.
Readjust, repair, or replace valve.
Clean strainer.
Indicated by pump inlet pressure dropping several pounds when
pump is started. Remove restriction or modify piping.
Replace.
Without vapor equalization, a pump can remove only about 3%
of the truck tank capacity per minute without severe cavitation
and capacity loss.
Reverse or replace sideplates. Check universal drive assembly
to make sure angularity is within limits, yokes are parallel and
slip-joint is greased. Check bearings.
Remove vanes and clean out foreign matter (check
strainer). Replace vanes if swollen.
Check valves. Make sure internal tank excess flow valve is
open! Refer to manufacturer's instructions.
Stop pump until valve opens. If problem continues, slow pump
down or install a new or larger excess flow valve.
Disassemble and inspect pump. Repair if necessary.
Service meter.
Clean out the pump—check strainer in suction line.
Clean out pump carefully and replace vanes. Has
pump been operated dry? Then, check for damage to cam and
rotor shaft assembly.
Replace pump bearings. Grease monthly. Use ball bearing
grease manufactured for intended service.
Let thaw and break loose carefully. Add alcohol to tank (on LP-
Gas). Check with product supplier about possibility of water
in gas.
Clean inlet strainer. Increase pipe size.
Set valve for higher pressure—see instructions.
Disassemble, inspect and repair as necessary. Do not run
pump dry!
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