Being a sophisticated device, when Pressure Reducing Valve (PRV) is subjected to the harsh working conditions, there could be chances of choking up of the valve which eventually leads to disruption in the outlet pressure, noise, vibration and inadequate flow. Downtime goes up along with the maintenance cost. This presentation talks about common issues, the root cause analysis and troubleshooting the same.

1. Troubleshoot and
Root Cause Analysis
Pressure Reducing Valve
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2. Do You Think?
● No Flow Condition is a problem?
● No Flow Condition can be corrected?
● Inlet Pressure = Outlet Pressure is known as No-Flow Condition?
● For any Inlet Pressure there would, surely, be an Outlet Pressure?
● Can Piston be hardfaced (Chrome Plating) to minimise wear & tear
resistance caused by Cavitation?
● Piston Stem failure is due to wrong design or raw material issue?
●
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3. 3
Troubles in PRV
Three Reasons:
1. Problem with the Piping System
a. Unflushed Line
b. Presence of Dirt / Foreign Particles in the water (No Strainer)
c. High Fluctuations in the Inlet Pressure (Faulty Pump design)
d. Use of single PRV instead of multiple PRV for high pressure reduction
e. Faulty By-Pass Line
2. Problem with the Operator
a. Smaller / Larger size of valve installed
b. PRV installed in wrong direction
c. Pressure Setting changed unknowingly
d. Missed out to clean strainer
3. Problem with the valve design (limitation)
a. Non effective sealing by O’ Rings
b. Use of Rubber O’ Rings limits the working temperature range
c. Spring MOC

4. No Flow Condition
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No Flow Condition is not a problem. It does not affect the working of PRV

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Other Possible Reasons
No Flow Condition is Not Same as Pressure Equalizing Condition
(Inlet Pressure = Outlet Pressure)
● Incorrect Pressure Setting due to the excessive tightening of the adjustment
screw which should be loosened / reset to rectify the trouble
● Critical seating mechanism within the valve could have been bent / broken due
to Cavitation or Abrasion through foreign particles.
● Due to leakage at the seat or seal, the upstream pressure passes to the outlet
● Spring is totally compressed
● Valve internals could have been damaged due to a water hammer
● The isolation valve of the by-pass or any other line may be faulty, which allows
the inlet pressure of the fluid to pass through it.

6. 6
Discharge vs Pressure Drop
At Pressure Drop of 0.4 Kg/sq. cm, the discharge ceases to ZERO

7. 7
Failed Piston Stem Issue
Possible Reasons:
● The Stem threading is damaged. This may be due to
various factors arising out of:
○ Presence of foreign particles
○ Sudden jerks of fluctuation in the inlet pressure
○ Damaged O’Rings due to which piston moves freely
and pressure on threading increases
○ Poor workmanship
● Due to severe Cavitation and Abrasion, the pitting of disc
and stem occurs which decreases the strength of the stem
Piston MOC is changed to Forged Brass with better mechanical properties
Hardfacing (Chrome Plating) doesn’t impart much strength to the Stem

8. 8
1. Outlet Pressure does not reach desired valve
Cause Test Solution
● Inlet Pressure is not adequate for
desired results
Maximum Outlet pressure is 85% of the
Inlet Pressure with a min DP = 0.4 Bar
Raise Inlet Pressure, if possible
● Adjustment is not proper Turn adjusting screw in clockwise direction Reset the PRV as per the procedure
● Disc is clogged Check the amount of scaling or dirt
particles accumulated on the disc surface
Clean the disc. If found damaged, change it
● Piston is damaged Close all the valves and remove fittings.
Dismantle the piston and the disc and
inspect
Change the piston
● Valve size is too small and can not
supply enough capacity
PRV is too small Resize and install larger valve
● Inlet Strainer is clogged Dismantle the strainer and check Clean the strainer and re-fit it
● The pressure gauge is out of order Check the gauge if it is OK Calibrate it or change it
● Damaged / Broken Spring Check if the Spring is damaged / broken Replace the Spring

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2. Outlet Pressure is higher than specified level
Cause Test Solution
● Adjustment is not proper Turn the adjusting screw in anti clockwise
direction and check the outlet pressure
Re-set the PRV as per the procedure
● Disc is clogged Check the amount of scaling or dirt
particles accumulated on the disc surface
Clean the disc. If found damaged, change it
● By-Pass valve is not shut or is leaking Check the bypass valve, shut it properly.
Check if it it leaking even then
Shut it properly, if leakage does not stop,
repair it or change it
● O’Ring is damaged Dismantle the valve and inspect the O’Ring Change the O’ring
● Spring is clogged or damaged Dismantle the valve and inspect the Spring Clean the Spring, if does seem working,
change it
● Variation / Malfunctioning of Pressure
Gauge
Check the pressure gauge with a calibrator Repair or Change the Pressure Gauge
● Excessive Back Pressure from the
heating appliances
Check if there is any check valve or back
pressure safety device used before the water
heater
Proper back pressure safety device needs to
be fitted before the heating appliance to
avoid water expansion to disturb the working
of the PRV

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3. Excessive Noise is present
Cause Test Solution
● Valve size is
under-dimensioned for the
flow rate
Recalculate the load Install correct size valve
● Too much pressure
reduction in the valve
Check the pressure ratio and
utilize the cavitation diagram
If the pressure ratio exceeds 2.5,
use multiple PRV in series for
step reduction of the pressure
● Excessive Air (air bubbles) in
the system
Check the presence of air in the
system
Use Air Release Valve to vent
out the unwanted air from the
system
Water Hammer due to any check
valve installed in the system
Check for the flapping /
bouncing of check valve
In the severe condition, use
water hammer arrestor or
non-slam check valve

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4. No Flow in the PRV
Cause Test Solution
● PRV is fitted in wrong direction Check the direction arrow of the valve. it
should be pointed toward the downstream
side
PRV being an Unidirectional valve should be
fitted in correct manner

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5. Leakage
Cause Test Solution
● O’Ring is damaged Dismantle the valve and inspect the
O’Ring
Change the O’ring
● Disc is clogged Check the amount of scaling or dirt
particles accumulated on the disc
surface
Clean the disc. If found damaged,
change it
● Plug Cap is damaged Check if the plug cap is damaged Change the Plug Cap

13. ● Flush the pipe lines before installing the PRV
○ This is recommended to avoid the foreign particles / dust passing through the PRV.
These particles obstruct the PRV’s smooth functioning causing damage/blockage
of the seating surface.
● Install a strainer in the main line before the PRV
○ The strainer serves to filter out the dust and dirt particles from the pipeline and
ensures smooth operation of PRV's.
Always Remember
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14. Quick Learning Points
● No-Flow Condition is an inherent design feature of a PRV. It is not a product fault. It
does not affect the working of PRV. It can not be corrected
● Pressure Equalization (Inlet = Outlet) may not be a synonymous to No-Flow Condition
● Hardfacing (Chrome Plating etc) of the Piston Stem does not yield any additional
benefits
● There shall be a minimum pressure drop of 0.4 Kg/sq Cm at which the discharge is
almost zero
● Most possible reason of Stem Failure is the Failure of the Stem Threading. Stem hardly
breaks in to pieces (or cracked)
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15. Thank You!
any question, please
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