Bell & Gossett S14141B 70X Multiple Pump Pressure Booster Systems - Manual (Page 11)

TROUBLESHOOTING COMBINATION PRESSURE REDUCING AND CHECK VALVES
11
DANGER: Troubleshooting live control panels exposes
personnel to hazardous voltages. Electrical trouble-
shooting must only be done by a qualified electrician.
FAILURE TO FOLLOW THESE INSTRUCTIONS COULD
RESULT IN SERIOUS PERSONAL INJURY, DEATH,
AND/OR PROPERTY DAMAGE.
APPENDIX D
1.0 System Pressure Higher than Desired Set Point
1.1 Primary Causes
a) Insufficient pressure on top side of diaphragm.
b) Leakage through main valve seat.
c) Pressure build-up due to thermal expansion,
such as caused by volumetric expansion of the
water in a heater connected to the system side
of the PRV.
d) Inaccurate system pressure signal.
1.2 Tests and Remedies (see Figure 2 for item numbers)
a) Install gauge, install on CRD (Item 6), if
necessary.
b) Vent air from air vent (Item 9) and from other
high points of PRV trim. Valve cover bolts may
have to be loosened on some units with PRV
mounted horizontally.
c) Check CRD set point adjustment.
d) Close stop cock (Item 7) in check line. If PRV
now operates properly, clean or replace adja-
cent check valve (Item 8).
e) Inspect CRD (Item 5) disc and seat for proper
seating.
f) Inspect strainer (Item 1) that the screen is clean.
g) Inspect orifice (Item 3) that it is not clogged.
h) Plug outlet side of CRD. If main valve closed
tight, the problem most likely is in the CRD.
Replace same. If the main valve does not close
tight, disassemble it for inspection. Check for
scored seat.
2.0 System Pressure Lower than Desired Set Point
2.1 Primary Causes
a) Excessive pressure on top side of diaphragm.
b) Suction pressure below design conditions
(check nameplate on panel door for design
conditions).
c) Desired system pressure is higher than design
condition (check panel nameplate).
d) Flow Rate is greater than design condition.
e) Inaccurate system pressure signal.
2.2 Tests and Remedies (see Figure 2 for item numbers)
a) Install gauge, install on CRD (Item 6), if
necessary.
b) Vent air from air vent and all high points.
c) CRD disc guide or yoke binding.
d) Check motor amps. If greater than full load
amps (motor nameplates), flow rate may be
greater than design.
e) Leak into upper diaphragm chamber. Close
stop cock (Item 7) and remove a connection
between the flow control valve (Item 4) and the
PRV valve cover. Plug the flow control side.
Open pump suction valve and start pump. If
water emits from the valve cover plate, there is
a leak passing the diaphragm into the upper
chamber.
f) Remove valve cover plate for inspection.
Remove "cancerous" buildups which may pre-
vent diaphragm from lifting fully. Check for
binding of valve stem assembly.
g) Opening speed control valve (Item 4)
clogged in restricted flow mode (out of PRV
valve cover).
h) Orifice (Item 3) missing. The orifice fitting identi-
cal in appearance to a flare to MPT adapter,
therefore may have been inadvertently replaced
or misplaced during valve service.
i) Check pump discharge pressure. Does it corre-
spond to the TDH curve?
3.0 System Pressure Slow to Recover from Under
Pressure to Set Point
3.1 Primary Causes
a) Pressure above the diaphragm is not being
removed quickly enough.
b) Mechanical binding in main PRV or CRD pilot
valve.
c) Excessive suction supply line pressure drop.
3.2 Remedies (see Figure 2 for item numbers)
a) Any of the items of 2.2 may be a contributing
factor.
b) Readjust flow control valve (Item 4) to less
restrictive setting, turn counter clockwise.
NOTE: Forcing the stem too far CCW will shear
the stem snap ring and cause the stem to blow
out. Recommend that the stem be initially turned
CW, noting the number of turns required to seat
the stem, then backing it out CCW a few more
turns than the original setting. The maximum
CCW setting is about 9 turns.
4.0 System Pressure Overshoots Greatly and Slow to
Recover to Set Point
4.1 Primary Causes
a) Pressure above the diaphragm is not being
applied soon enough.
b) Mechanical binding in main PRV or CRD pilot
valve.
c) Leaky seat in main PRV or CRD valves.
d) Excessive suction supply line pressure drop.
e) System side surge (water hammer) due to
sudden closure of a quick opening valve.
f) Strainer (Item 1) clogged.
4.2 Remedies (see Figure 2 for item numbers)
a) Any of the items of 1.2 may be contributing
factors.
b) Install larger orifice (Item 3).