070.610-IOM (JUL 21)
Page 39
RWF II Rotary Screw Compressor Units
Maintenance
Table 11: Thrust bearing assembly adjustment
Pump
Distance (in.) on O.D.
End clearance
size
of bearing housing
(in.)
GG
7/16
0.003
HJ, HL
9/16
0.003
AS, AK, AL
1/2
0.003
Installing carbon graphite bushings
When installing carbon graphite bushings, extreme
care must be taken to prevent breaking. Carbon graph
-
ite is brittle and easily cracked. If cracked, the bushing
will quickly disinte grate. Using a lubricant and adding a
chamfer on the bushing and the mating part will help in
installation. The additional precautions listed below must
be followed for proper installation:
1.
A press must be used for installation.
2.
Be certain bushing is started straight.
3.
Do not stop pressing operation until bushing is in prop
-
er position. Starting and stopping will result in a cracked
bushing.
4.
Check bushing for cracks after installation.
Troubleshooting the demand pump
DANGER
Before opening any pump liquid chamber (pumping
chamber, reservoir, jacket etc.) Ensure:
1. That any pressure in chamber has been completely
vented through suction or discharge lines or other
appropriate 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
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.
