Pressure Reducing Valve (PRV) - Part1

Pressure Reducing Valve or simply PRV is a type of valve which is used to reduce the downstream pressure to the desired level in any piping system. It is generally used where the main line carries the fluid at very high pressure and it is advisable to reduce the pressure in the branch line to save the appliances from getting damaged due to the impact of high pressure. Not only the pressure, it also helps in reducing the water wastages, noise and vibration, water hammering effect thus minimizing the maintenance cost and maximizing the life of the appliances like pipe fittings, taps, water heater etc

1. Pressure
Reducing
Valve
1

2. Do You Think?
●Reducing Pressure is the only output of a Pressure Reducing Valve?
●Pressure Reducing Valves are installed in Series, only?
●Cavitation can be avoided only by maintaining Pressure Ratio of 2.5?
●PRV maintains constant Outlet pressure with fluctuations in Inlet Pressure?
●Temperature has no effect on Cavitation?
●Pressure Reducing Valve is a Pressure Control Valve?
●The maximum working temperature is 80 degree C
●Spring force is the only factor behind reducing the pressure?
●Unlimited numbers of PRV can be installed in Series?
●PRV reduces water hammering and noise in the pipeline?
●PRV saves lot of water from wasting?
●It is not recommended for Oil application?

2

3. Pressure Reducing Valve (PRV)
PRV is a device used for reducing the
pressure of water in the pipeline to the
desired level at its actual point of use and
thereafter, regulating it continually, on its
own.
Uses:

●To keep the pressure of the water constant in
the distribution network
●To avoid excessive wastage of water
●To keep the water pressure constantly below
the maximum value allowed
First Pressure Reducing Valve was developed in the
year 1876 by Watt Industries 3

4. Types of PRV
1.Direct Acting
○Piston type
○Diaphragm type


2.Pilot-Operated
○Internally Pilot-Piston Operated
○Externally Pilot Operated
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5. Types of PRV contd..
Direct Acting Pilot Operated 5

6. 6
Types of PRV contd..
Direct Acting PRV

Used for small loads where extremely close
pressure control is not needed.

●Pros: Compact size, low price, easy to
install.
●Cons: Higher droop (variation from set
pressure) than Pilot-operated PRV

Direct-operated valves are used when loads are
small and some downstream pressure
variations may be accepted. They are generally
used in light load services




Pilot Operated PRV

Used for larger loads where close pressure
control is required

●Pros: Close pressure control, fast response
to load variation, may be used across a
broader range of flow rates than the direct
acting types.
●Cons: Larger size, higher price.
Pilot-operated pressure reducing valves can
respond quickly to varying load conditions
while maintaining stable secondary pressure
where precise pressure control is needed. They
are generally intended for larger load
applications.

7. Working Principle
Piston Type PRV is based upon principle of Venturi Effect
and Equilibrium of Forces.
There are three forces acting on the fluid (water) between
the Inlet and the Outlet Ports. These Forces are:

1.Reduced Pressure (after Seat),
2.Back Pressure (acting on the underside of the piston)
3.Spring Force


Three Steps are involved:
●Pressure is reduced due to reduction in the cross
sectional area (bore) and amount of opening of the disc
(higher the opening higher the Outlet Pressure)
●Back Pressure tends to close the seat
●Spring Force which tends to open/close the Seat w.r.t
Pre-Set condition
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8. Working Principle contd..
PRV's are factory preset to specific pressure
output ranges but can be adjusted further by
increasing or reducing the tension on the
spring using an adjustment screw nut.
P
Pressure Drop
= P
Reduced
- P
Back Pressure
+/- P
Spring
Force


P
Outlet
= P
Inlet
- P
Pressure
Drop


Venturi Effect 2
8
Venturi Effect 1

9. Key Benefits
Maintains Constant
Downstream Pressure at
desired level
Reduces Water Wastage
Reduces Water Hammering
and Noise
Reduces Maintenance Cost
Saves Energy. Saves Money
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10. Facility provided to install
pressure gauge
Single Valve for wide range of
pressure (25 Bar max Inlet to 0.5 Bar
min outlet
Easy to install
Requires less maintenance
Noiseless
Salient Features of Piston Type PRV
Piston Operated, having long life as
piston is of forged brass
Needs less space to install
Easy Pressure setting
Cost Economic
Rugged body, compact in design
Most of the critical working components
have a distinct edge of being hot brass
forged
All 'O' rings of superior food grade
material, hence ensuring absolute
zero health hazard
Suitable only for water application, due to Rubber O’Rings, limited range of temperature and chemical reactivity (Oil etc)
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11. Key Benefits cont...
Reduces Water Wastage
Reducing the pressure from 7
Bar to 3.5 Bar will result in a
saving of approximately 1/3
because 1/3 less water flows at
this lower pressure.

A moderate savings would result
if your supply pressure was
reduced to 5.5 Bar However, even
at this lower pressure, savings
with a PRV would be 20%
A tap running for 10 minutes 11

12. Key Benefits cont...
Reduces Water
Hammering & Noise

The abrupt stoppage of high speed
water causes a “bounceback” of the
water and is called Water Hammer,
causing banging pipes, noisy systems
and damage to appliance.

Using a PRV can control the water
hammering effect and reduces the
maintenance & replacement cost.
PRV reduces maintenance cost of piping and fittings
Water Hammering
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13. PRV for Buildings
Solution: install a pressure
reducing valve at the input of
each flat.
Therefore, if you install a single
central pressure reducing valve
at the bottom of the building
adjusted to 3 bar, the first
storeys will be supplied at the
right pressure, but the more you
go up the storeys, the more the
pressure will drop.
*consider a height of 3 metres for each storey and a load loss per storey of 0.3 bar.
Case No. 1: 6-storey building - « Normal » water mains pressure: 6 bar - Desired pressure in each flat: 3 bar.
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14. PRV for Buildings contd...

Solution: In the case of a
residential building where the
mains water pressure is very
high, you are advised to
install on the main inlet a
pressure reducing valve of a
larger diameter, which will
firstly reduce the pressure to 6
bar, and a pressure reducing
valve adjusted to 3 bar at the
entry of each flat.
*consider a height of 3 metres for each storey and a load loss per storey of 0.3 bar.
No PRV is required at the top floors as the pressure is
more or less the same as required
Case No. 2: Building of more than 6-storeys - « High » water mains pressure: 10 bar - Desired pressure in
each flat: 3 bar.
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15. PRV for Buildings contd...

In this case, the installation of a
pressure booster is necessary.
This will be adjusted to a value
of 5 or 6 bar, the purpose being
to obtain adequate pressure at
all floors. It is therefore
necessary to install the same
pressure reducing valve,
adjusted to 3 bar, at the entry
of each flat.
For very high buildings, the highest storeys do not require the installation of a pressure reducing valve
when the pressure is less than 3 bar.

Case No. 3: Building of more than 6-storeys - « Low » water mains pressure: 3 bar. Desired pressure in each
flat: 3 bar.
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16. 16
PRV for Buildings contd...
Case No. 4: Water Supply from the Overhead Tank

17. Cavitation
If the differential of pressure between the upstream
and the desired downstream is too large, then it will
be necessary to reduce the pressure in several
stages by installing a series of pressure reducing
valves. A high inlet pressure and a low downstream
pressure can cause a deterioration of the valve by
Cavitation.

In simple words Cavitation is a phase that is
characterized by a liquid-vapour-liquid process, all
contained within a small area of the valve and within
microseconds. Minor cavitation damage may be
considered normal for some applications, which can
be dealt with during routine maintenance. If
unnoticed or unattended, severe cavitation can limit
the life expectancy of the valve. Temperature has
almost no effect on Cavitation

Cavitation
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18. 18

19. The cavitation diagram shows the three operating
zones of the pressure reducing valve in function to
the inlet and outlet pressures:

ZONE 1: Cavitation Zone: The cavitation phenomena
is clearly evident in this zone. It is recommended to
refrain from using pressure reducing valve under
such pressure differential conditions.

ZONE 2: Critical Zone: The possible occurrence of
cavitation phenomena inside the pressure reducing
valve is evidenced. It is recommended to avoid using
the pressure reducing valve at these pressures
differential conditions.
ZONE 3: Safe operating zone: Here the pressure reducing valve operates in optimum conditions
and there is no cavitation in this Zone. This is the optimum interval of pressure values for the
operation of the pressure reducing valve.


Cavitation Diagram
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20. Selection of PRV (A Typical Example)
PRV in Series
For Example:

Inlet Pressure = 13 Bar
Outlet Pressure = 3 Bar

It falls in Cavitation Zone (as depicted in Cavitation Diagram)

Solution: Use two PRV’s in series to achieve the desired
pressure differential.

PRV - 1

Inlet Pressure = 13 Bar
Outlet Pressure = 6 Bar (pressure ratio: 13/6 = 2.17 < 2.5)

PRV - 2

Inlet Pressure = 6 Bar
Outlet Pressure = 3 Bar (pressure ratio: 6/3 = 2.0 < 2.5)

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21. Installing PRV’s in Parallel connection
Parallel installation is
recommended for
applications with a wide
variation of reduced
pressure requirements and
where a continuous water
supply must be
maintained. Parallel
installations offer the
advantage of providing
increased capacity beyond
that provided by a single
valve and improve valve
performance for widely
variable demands.
Parallel Connection with Smaller Size
Valves or Same Size Valves
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22. Size and type of pipe
Maximum inlet pressure
Minimum required downstream pressure
“While selecting a PRV, the pipe size alone is not necessarily the determining factor.
The above factors must be considered”
Pressure Reducing
Valve (PRV)
Selection
Water demand in amount (e.g. LPM)
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23. PRV Installation
Zoloto pressure reducing valves may be installed in any positions.

❏Horizontal
❏Vertical
❏Bottom side up
❏Inclined
Generally installed in high rise buildings at inlet of each floor
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24. Pressure Setting of PRV
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25. ●Install the PRV on the pipe as shown in the layout diagram
and open the cap (part no. 14)

●Release the adjusting ring by rotating it, anti-clockwise with
the help of a screwdriver so that the PRV comes in fully closed
position.

●Set the inlet pressure you want to feed into the PRV and check
the same on Pressure Gauge-1

●In order to adjust the outlet pressure, close the valve ‘Y' and
open the valve 'X'. Now turn the adjusting ring (part no. 13) in
clockwise direction slowly until you see the needle of pressure
gauge-2 showing a rise in pressure & stop rotating it just
before the desired outlet pressure is attained.

●Now open the valve 'Y' to release the pressure once and close
it again.
Pressure Setting of PRV contd..
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26. Pressure Setting of PRV contd..
●Watch the Pressure Gauge-2. The needle of the gauge should point to the set
pressure, if there is any deviation+/_ please adjust the same by moving the
adjusting ring accordingly in clockwise or anticlockwise direction, until the desired
pressure is achieved.

●Please remember that the rotational movement of adjusting ring in clockwise
direction increase the outlet pressure and anticlockwise direction decreases the
same, on the outlet side.

●When the outlet pressure is adjusted to the desired level, please close the cap
(part no. 14)

●Plug-1 is only a cover to protect the thread provided for installation of 1/4" BSP
sized pressure gauge.
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27. Precautions
❏Although Pressure reducing valves needs no maintenance but
the rubber “O” rings inside the PRV are very sensitive to scale,
impurities, or any foreign particles so it's always recommended
to flush the line thoroughly and install a strainer in the main
line.


❏In the case of a residential building, it is advisable to install a
pressure reducing valve at the input of each flat, and not a
centralized pressure reducing valve at the bottom of the
building.
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28. Troubles in PRV
●Foreign particles (sand, dust, welding splinters) accumulated inside PRV which
damaged the 'o' ring.

●PRV installed in reverse direction of arrow marked.

●Strainer is not provided before the PRV.

●Too much variation in inlet pressure.

●User not aware about that how to set the pressure.

●Bye pass line not provided.

●Lack of knowledge for inlet pressure.

●PRV installed in such a position i.e very near to the wall, where it cannot be
serviced.
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29. Troubleshooting
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30. ●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.
Troubleshooting contd..
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31. Correct Sizing of PRV
In order to avoid cavitation phenomena, it is recommend to:

❖Utilize the “CAVITATION DIAGRAM”
➢This diagram helps to understand about Cavitation Zones and to select the
correct size of the valve

❖Use correct Pressure Ratio
➢The ratio between the maximum inlet pressure and the regulated pressure
should not be more than 2.5

❖Install more numbers of Pressure Reducing Valves
➢To achieve the desired pressure differential, use more numbers of pressure
reducing valves in series or parallel connections

❖Choose Optimum Speed value of the Fluid
➢Select the diameter of the PRV (valve size) so that speed (velocity) of the fluid
passing through it is between the recommended values (V= 0.7 - 1.5 m/s for residential
use and V= 1 - 3.5 m/s for industrial use)
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32. Pressure Drop vs Flow Rate
For Example:

Inlet Pressure: 4.8 Bar
Outlet Pressure: 3.0 Bar
Size of PRV: 40 mm (1½”)

Pressure Drop (Head Loss) =
Inlet Pressure - Outlet Pressure

= 4.8 - 3.0 = 1.8 Bar

Flow Rate (Discharge) will be 3.1 Litre per sec (186 LPM) as calculated from the above diagram
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33. Maintenance
Video
PRV Pressure
Setting Video
PRV Videos
Pressure Reducing Valve
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34. PRV Pressure Setting
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36. Quick Learning Points
●Apart from reducing pressure, PRV reduces noise, water hammering and water wastage
●PRV can be installed in Series as well as Parallel connections
●Cavitation can be controlled by maintaining Pressure Ratio of 2.5, selection larger size PRV and
reducing fluid velocity within the recommended limits
●PRV maintains constant Outlet pressure with uptp 10% fluctuations in Inlet Pressure?
●Temperature has negligible effect on Cavitation?
●Pressure Reducing Valve is not a Pressure Control Valve as it can not increase pressure
●The maximum working temperature is 90 degree C instead of 80 degree C
●Spring force and Back Pressure are important factors to reduce pressure apart from design
●The minimum Outlet Pressure is 0.5 Bar. It restrict installing more numbers of PRV in series
●PRV saves appx. 30% of water from wasting
●It is not recommended for Oil application as Oil deteriorates rubber O’Rings
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37. Thank You!
any question, please
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