1. Adca Training
Part 4
This presentation is only a guideline, that can only be completed by a trained personel.
Adca Steam Equipment
Training.10 E 10.08

2. Training Contents Part 4 Pressure Reduction
Safety Relief Valves and Other Steam Valves
Part 5
Control Valves
Components of Control Valves
Humidification

3. Pressure Reducing Valves
Why ?
Industrial fluids are usually distributed from pressurizing stations, boiler houses, etc, which operate with predefined pressures.
Users not always assume the original pressures, thus it turns out to be necessary to reduce pressure close to usage points (machinery) or in different areas of a plant, simply for mechanical or thermodynamic reasons.
High pressures distribution can be convenient namely with compressible fluids, such as saturated steam, as a mean of decreasing investment through the usage of smaller section piping and reducing pressure only close to the user. Assuring not only a stable pressure in usage but also higher latent heat, which represent less steam consumption and less loss of flash steam from open vents on condensate tanks, etc.
Therefore, whether for security, functioning or energy saving matters, pressure reducing valves are a resident member on several fluids systems.
Saturated steam temperature is directly related to it’s pressure and so, the pressure control can be also an affective method of temperature control mainly in those equipments where it is not possible to install a temperature probe in the right place (i.e. Sterilizers, cooking, contact dryers, ...).

4. Small loads where accurate control is not crucial.
Pressure Reduction Valves
Direct Acting
Small loads where accurate control is not crucial.
Large flows and main lines where inlet pressure do not have wide variations.
PRV25
PRV31SS
RP45
(Balanced or
Unbalanced plug)
(Balanced plug)
(Balanced plug)
The reduced pressure acts on the underside of the diaphragm, bellow or piston so balancing the load of the pressure adjustment spring and moving the inner valve through a spindle to obtain the desired controlled pressure.

5. Large flows where accurate control is required.
Pressure Reduction Valves
Pilot Operated
The reduced pressure medium through a controlled pressure pipe, acts on the underside of the diaphragm of a pilot which, in turn supplies steam (or gas) at variable pressure into the upper chamber of the piston operator, which regulates the main inner valve.
In both options, pressure setting is adjusted by varying the pressure exerted by the control spring by turning the adjustment hand wheel.
PRV47
Large flows where accurate control is required.

6. Pressure Reducing Valves
Which valve: Direct acting or Pilot operated?
10 barg reducing to 1 barg
A 25mm PRV47 will pass 944kg/h
A 25mm PRV25 will pass 105 kg/h
This is why it is imperative to size and select the valve to the application and not to existing line size!

7. Pressure Reduction Station
Example 1000 kg/h steam at 10 bar g reducing to 2 bar g
DN50 x 80 safety valve set at 2.5 bar g
capable of passing 2102 kg/h
DN 50mm Inlet pipework
Steam
PRV47 DN32
Max. output 1468 Kg/h
DN 100mm Outlet pipework
S25 Humidity separator DN ½” mains drainage trap set
Valve selection diameter must be done according to the actual flow of steam, liquid or gas passing through the valve, the minimum inlet pressure and the desired reduced pressure.

8. Pressure Reducing Valves
Self – Acting pressure Controls
Which Valve and For Which Application?
PRV25
PRV300
PRV47
PRV31
RP45
PRV30
PRW25
P15
PRV25
PRV25
PRW25
RP45
PRV47
P15
PRV31
PRV30
PRV300
Low Pressure Steam (Special)
Steam
Liquid
Gas

9. Pressure Reducing Valves
PRV25
Advantages
Disadvantages
Low Cost
Low flow rates
Bellow sealed
Possible spring hysteresis
Reliable
Crude control

10. Pressure Reducing Valves
RP45
Advantages
Disadvantages
Low Cost
Need a water seal
Reliable
Possible spring hysteresis
High flow rates
Relative crude control

11. Pressure Reducing Valves
PRV47
Advantages
Disadvantages
Controlled control
More expensive
Low springs hysteresis
Sensitive to bad quality fluid
High flow rates
More complex maintenance
Reliable

12. Pressure Reducing Valves
Questions to ask
Medium passing through valve
Upstream and downstream pressure
Flow rate (maximum and minimum, if applicable)
Body material preference
Pipeline connections

13. Pressure Reducing Valve
How to Select
There are 2 methods for pressure reduction selection:
Kv calculation and selection
Table of selection
The Kv values should be calculated according to the formulas illustrated in the next page.
The table of selection is present in the datasheets of some equipments or alternatively the valve Kvs.
Two valves in series can be preferable in case of big reductions.
Two valves in parallel are recommended in case of wide load fluctuations.

14. Calculation of Kv value
Pressure Reducing Valve
How to Select
Calculation of Kv value
Pressure Drop
Medium
Liquids
Saturated
steam
Gases a) b) Kv
Flow coefficient
m3/h P1
Upstream absolute pressure
bar P2
Downstream absolute pressure Dp
Pressure drop (P1 – P2) Q1
Flow rate Q2
Kgs/h Q3
N.m3/h (0ºC – 1013 mbar) d1
Specific weight of liquid
Kg/m3 d2
Specific weight of gas T
Absolute temperature (T=273 + t ºC) ºK t
Fluid temperature ºC

15. Pressure Reducing Valve
How to Select
Example 1 – Calculation by Kv Selection
Operation conditions:
Fluid = Water
P1 (Upstream pressure) = 10bar g (11bar a)
P2 (Downstream pressure) = 6bar g (7bar a)
ΔP = 11-7 =4 bar
Q (Flow rate) = 13 m3/h
d (Density) = 1000 Kg/m3
Required material: Stainless steel
According to the table the formula to be used is
We will consider for this case a safety factor of 20%.
We can now select the correct size of valve.

16. Pressure Reducing Valve
How to Select
Example 1 – Calculation by Kv Selection
Looking at the datasheet of the PRV30SS (stainless steel construction) we have the following table:
So the valve PRV30SS DN40 is suitable for the application.

17. Pressure Reducing Valve
How to Select
Example 2 – Calculation by Kv Selection
Operation conditions:
Fluid = Compressed air
P1 (Upstream pressure) = 28bar g (29bar a)
P2 (Downstream pressure) = 10bar g (11bar a)
Q (Flow rate) = 220 Nm3/h
d (Density) = 1,293 Kg/m3
t (Temperature) = 20ºC
T (Absolute temperature) = 293 ºK
Required material: Stainless steel
According to the table of formulas since the formula to be used is
We will consider for this case a safety factor of 20%.
We can now select the correct size of the valve.

18. Pressure Reducing Valve
How to Select
Example 2 – Calculation by Kv Selection
Looking at the datasheet of the PRV30SS we have the following table:
So the valve PRV30SS DN15 is suitable for this application.

19. Pressure Reducing Valve
How to Select
Example 3 – Calculation by Valve Capacity Table: PRV47 and RP45
Operation conditions:
Fluid = Saturated steam
P1 (Upstream pressure) = 12bar g
P2 (Downstream pressure) = 5bar g
Q (Flow rate) = 1200 Kg/h
Requested valve material: Steel
With this we can now use the valve selecting table and choose the correct size.

20. Pressure Reducing Valve
How to Select
Example 3 – Calculation by Valve Capacity Table: PRV47
Valve:
Looking to the capacity table on the PRV47 datasheet we should consider a valve PRV47 DN32 for this application.
Regulation spring:
From pressure range spring table, the black spring (2 to 17 bar) is adequate.
NOTE: Pressures shown in the table are pressure gauges.

21. Pressure Reducing Valve
How to Select
Example 3 – Calculation by Valve Capacity Table: RP45
Valve:
Pressure ratio:
So, the figures from capacity table can be taken without the use of any corrector factor and we should consider a valve RP45 DN32 for this application.
Actuator and Regulation spring:
From the respective table we realise that the spring Nr. 60 in combination with A-21 actuator guaranty a downstream pressure regulation between 3,9 and 5,5 bar.
NOTE: Pressures shown in the table are pressure gauges.

22. Pressure Sustaining Valves
PS47
Critical applications
Minimum 7 bar
Compressed air
≈ 8 bar
NOTE: Compressor capacity on the limit.
Non- critical applications
PS47
(Closed up to 7 bar)
Pressure in line will decrease in case of overage consumption. When it reaches 7bar pressure sustaining valve closes, maintaining the available flow to assure functioning of critical applications.

23. Safety Valves Questions to ask Set pressure
Flow rate safety valve is required to pass
Medium valve is to pass
Pipeline connections
Body material of valve
Safety valve has to be able to pass whatever the Pressure Reducing valve can pass if it ever fails fully open, therefore we need to know exact size, make and model of PRV and upstream pressure
If safety valve is for a steam boiler application then we need to know maximum output of the boiler.
If safety valve is for a water or pump application we need to know the maximum the pump will pump

24. Safety Valves How do we size the Safety Valve? Safety set at 2.5 bar g
Safety valve DN80x125 Capable of passing 5148 kg/h
How do we size the Safety Valve?
PRV47 DN50
Design conditions:
2500 Kg/h of steam
Inlet 10 barg – Outlet 2 barg
Max.permissible flow
through the valve: 3718 Kg/h
(See capacity table)
Safety set at 2.5 bar g
In case of PRV failure in open position the safety valve is able to pass the maximum possible flow rate permitted.

25. Complete Steam Diagram