6
Problem Identification Procedures
When using differential pressure gauge
Check differential across No. 1 check valve
READING
PROBLEM
2 to 3 psid
Leak in No. 1 or No. 2 check valve
4 to 7 psid and steady
Malfunctioning pressure relief valve
2 to 7 psid
Inlet pressure fluctuation
Without using differential pressure gauge
A. Close gate valve No. 2
RESULT
PROBLEM
If discharge stops
Leak in No. 2 check valve
If discharge does not stop Go to B
B. Open No. 4 test cock to produce a flow greater than
differential relief valve discharge
RESULT
PROBLEM
If discharge stops
Leak in No. 1 check valve
If discharge does not stop Malfunctioning pressure relief valve
PROBLEM
CAUSE
SOLUTION
Assembly discharges from differential relief valve during
no flow condition
Fouled first check
Disassemble and clean check valve #1
Fluctuating inlet pressure
Control supply line water pressure
Install a soft-seated, spring-loaded check valve upstream
of the assembly
Outlet pressure higher than inlet pressure and leak in
check valve #2
Disassemble and clean check valve #2 and identify cause
of backpressure
Leak through diaphragm or around flange bolt holes of
relief valve
Service relief valve
Pressure relief valve does not close
See problem 'Pressure relief valve does not close'
Assembly discharges from differential relief valve during
a flow condition
Check valve #1 wedged open
Disassemble and clean check valve #1
O-ring displaced from groove in check #1
Disassemble and replace
Pressure relief valve does not close
See problem 'Pressure relief valve does not close'
Fluctuating line pressure
Install pressure sustaining check upstream of backflow
Differential pressure relief valve does not open during test
Differential pressure across check valve #1 stays above
2.0 psi due to leaking outlet gate valve
Repair shutoff valves
Weak or broken relief valve spring
Disassemble and replace relief valve spring
Shutoff seat tube bound in body
Disassemble and repair
Plugged hydraulic hose
Disassemble and repair
Pressure relief valve does not close
Debris on sealing surface
Remove relief valve and clean
Plugged hydraulic hose
Disassemble and clean
Damaged seat or rubber shutoff disc
Remove relief valve assembly and replace
Ruptured diaphragm
Disassemble and replace diaphragm
Wrinkled or improperly installed diaphragm
Disassemble and properly position diaphragm
Troubleshooting
