RWH ROTARY SCREW COMPRESSOR UNITS
MAINTENANCE
070.620-IOM (DEC 12)
Page 29
TROUBLESHOOTING THE PUMP
DANGER
BEFORE OPENING ANY PUMP LIQUID CHAMBER (PUMP-
ING CHAMBER, RESERVOIR, JACKET, ETC.) ENSURE:
1. That any pressure in the chamber has been completely
vented through suction or discharge lines or other ap-
propriate openings or connections.
2. That the driving means (motor, turbine, engine, etc.)
Has been “locked out” or made non operational so that it
cannot be started while work is being done on the pump.
FAILURE TO FOLLOW ABOVE LISTED PRECAUTIONARY
MEASURES MAY RESULT IN SERIOUS INJURY OR DEATH.
Mark valve and head before disassembly to ensure proper
reassembly.
If trouble does develop, one of the first steps toward find
ing the difficulty is to install a vacuum gauge in the suction
port and a pressure gauge in the discharge port. Readings
on these gauges often will give a clue as to where to start
looking for the trouble.
Vacuum Gauge—Suction Port
1. High reading would indicate:
a. Suction line blocked foot valve stuck, gate valve
closed, strainer plugged.
b. Liquid too viscous to flow through the piping.
c. Lift too high.
d. Line too small.
2. Low reading would indicate
a. Air leak in suction line.
b. End of pipe not in liquid.
c. Pump is worn.
d. Pump is dry should be primed.
3. Fluttering, jumping, or erratic reading:
a. Liquid vaporizing.
b. Liquid coming to pump in slugs possibly an air leak
or insufficient liquid above the end of the suction pipe.
c. Vibrating from cavitation, misalignment, or damaged
parts.
Pressure Gauge - Discharge Port
1. High reading would indicate:
a. High viscosity and small and/or long discharge line.
b. Gate valve partially closed.
c. Filter plugged.
d. Vertical head did not consider a high specific gravity
liquid.
e. Line partially plugged from buildup on inside of pipe.
f. Liquid in pipe not up to temperature.
g. Liquid in pipe has undergone a chemical reaction and
has solidified.
h. Relief valve set too high.
2. Low reading would indicate:
a. Relief valve set too low
b. Relief valve poppet not seating properly.
c. Too much extra clearance.
d. Pump worn.
3. Fluttering, jumping, or erratic reading:
a. Cavitation.
b. Liquid coming to pump in slugs.
c. Air leak in suction line.
d. Vibrating from misalignment or mechanical problems.
Some of the following may also help pinpoint the problem:
1. Pump does not pump.
a. Lost its prime air leak, low level in tank.
b. Rotating in wrong direction.
c. Motor does not come up to speed.
d. Suction and discharge valves not open.
e. Strainer clogged.
f. Relief valve set too low, relief valve poppet stuck open.
g. Pump worn out.
h. Any changes in the liquid system, or operation that
would help explain the trouble, e.g. new source of
supply, added more lines, inexperienced operators, etc.
i. Tighten end clearance.
j. Head position incorrect.
2. Pump starts, then loses its prime.
a. Low level in tank.
b. Liquid vaporizing in the suction line.
c. Air leaks or air pockets in the suction line; leaking air
through packing or mechanical seal.
d. Worn out.
3. Pump is noisy
a. Pump is being starved (heavy liquid cannot get to
pump fast enough). Increase suction pipe size or
reduce length.
b. Pump is cavitating (liquid vaporizing in the suction
line). Increase suction pipe size or reduce length; if
pump is above the liquid, raise the liquid level closer
to the pump; if the liquid is above the pump, increase
the head of liquid.
c. Check alignment.
d. May have a bent shaft or rotor tooth. Straighten or
replace.
e. May be a foreign object trying to get into the pump
through the suction port.
4. Pump not up to capacity
a. Starving or cavitating increase suction pipe size or
reduce length.
b. Strainer partially clogged clean.
c. Air leak in suction piping or along pump shaft.
d. Running too slowly is motor the correct speed and
is it wired up correctly
e. Relief valve set too low or stuck open.
f. Pump worn out.
g. Tighten end clearance.
h. Head position incorrect.
5. Pump takes too much power.
a. Running too fast is correct motor speed, reducer
ratio, sheave size, etc. being used.
b. Liquid more viscous than unit sized to handle heat
the liquid, increase the pipe size, slow the pump down,
or get a bigger motor.
c. Discharge pressure higher than calculated check
with pressure gauge. Increase size or reduce length
of pipe, reduce speed (capacity), or get bigger motor.
d. Pump misaligned.
e. Extra clearance on pumping elements may not be
suffi cient for operating conditions. Check parts for
evidence of drag or contact in pump and increase
clearance where necessary
6. Rapid Wear.
a. Examination of a pump that has gradually lost its
ability to deliver capacity or pressure would show a
smooth wear pattern on all parts. Rapid wear shows
up as heavy grooving, galling, twisting, breaking, or
similar severe signs of trouble.