Crown CT4QP Series, Installation And Operation Manual

Page: 13 / 26

SECTION J: TROUBLE SHOOTING
J-1) PUMP FAILS TO PRIME OR PRIMES SLOWLY
1. Slow priming or failure of pump to prime is in most every
instance the result of an air leak in the suction line of the pump
or leaking/cut o-rings in the pump cleanout cover.
2. The most common source of air leaks are the threaded
connections of the suction line. These connections should be
coated with pipe thread compound and drawn up tight.
If a union is used it should be of the gasket type instead of the
ground joint type.
If quick connection couplings are used examine their gaskets
or o-rings.
3. A plugged suction line or a collapsed suction hose liner is
frequently the cause. Generally a collapsed hose liner cannot
be detected by removing the hose and looking through it.
Reversing the ends of the suction hose will in most cases correct
the problem for a while.
4. Make sure that the pump case has an adequate supply of
liquid.
5. Make sure the pump speed is fast enough. High lifts require
faster pump speeds.
6. Occasionally gaskets shrink and admit air into the pump.
Tighten gasket connections or replace them. On trash type
pumps, the case cover o-rings should be checked. When
replacing o-rings or gaskets, make sure they are well greased
for easy installation.
7. The bottom drain plug on trash pumps is on the suction side
and may not be tight.
8. The mechanical shaft seal may leak air if worn. If the grease
cup does not use grease, remove the cup, clean it, and fill it with
light oil. If the shaft seal is leaking, it will suck the oil into the
pump when trying to prime.
9. If the pump is old or has had much usage, check the internal
parts.
The impeller and volute could be worn out, or the impeller blades
plugged or damaged.
J-2) PUMP FAILS TO DEVELOP SUFFICIENT PRESSURE
OR CAPACITY
1. Check pump speed. A slow running pump will not deliver
much capacity or pressure head.
2. Check suction hose, strainer or suction end guard, it may be
partially plugged. Suction hose liner may be collapsing. See
paragraph 3 in previous section.
3. If possible check suction lift with a vacuum gage. Most of the
larger pumps provide a place for mounting a vacuum gage on
the suction flange. A vacuum of 15 or more inches of mercury
can cause considerable reduction in capacity. Lifts over 20 feet
are too generally high for efficient operation.
Each inch of vacuum Hg equals 1.13 feet of suction.
4. Check length of suction line. Long suction lines have the
same effect as a high suction lift because of increased friction
encountered when the liquid passes through the line.
5. Check the pump for worn parts. Worn parts such as an
impeller or volute will cause a reduction in both capacity and
pressure.
6. Check impeller for clogging. If the impeller is plugged with
oversize solids, a reduction in both capacity and pressure will
occur.
7. Check piping layout. If pump speed cannot be increased, it
may be necessary to increase the diameter of the piping or hose
and reduce the number of elbows or fittings in order to get more
capacity and head at the discharge. It is just a matter of pipe
friction loss, larger pipe has less friction.
8. Check the pump performance curve. The original selection
of the pump may have been too small for the intended job,
especially after it has received some wear.
13