Pressure Regulator Valves Diaphragm Material

[From:http://instrumentation.web.id] [Author:admin] [Date:11-08-17] [Hit:]

All pressure regulator valves (both maintain downstream and upstream) are utilizing a diaphragm as a tools to convert the spring force to pressure (P=F/A). Different with diaphragm at control valves which are not in contact with services fluid, diaphragm at pressure regulator valves does in contact with services fluid. It’s in contact because pressure regulator valves sense the downstream or upstream pressure directly through the diaphragm. If the downstream or upstream pressure is high enough to make the diaphragm push out it will make the valve close.

Since the diaphragm at pressure regulator valves is in contact with services fluid, it will have different selection method with the control valve diaphragm. So, how to select the diaphragm material for pressure regulator valves?

In general, diaphragm materials for pressure regulator valves are available in form of rubber and also metal. The use of metal diaphragm is quiet reasonable since the diaphragm is consider as a wetted part of the pressure regulator valves, thus it shall have same characteristic with other wetted parts. The only consideration that we shall take to use metal diaphragm is only the higher price than rubber diaphragm. The metal diaphragm usually comes in form of stainless steel, and monel. The rubber diaphragm usually comes in form of Buna N, Viton, Silicone, and Neoprene.

To select diaphragm material of pressure regulator valves, we shall consider the operating temperature at first step. If we are intending to use metal diaphragm, then we don’t need to worry about it since the diaphragm will also have the same temperature resistant like other wetted parts.

Below is the general operating temperature of some rubber:

Diaphragm Material Typical Temperature Services Ranges
Buna N / Nitrile (NBR) -65 oF to +250 oF
Fluorocarbon (FKM) / Viton -10 oF to +400 oF
Silicone (VMQ) -80 oF to +425 oF
Neoprene (CR) -40 oF to +250 oF

 

After we select the appropriate diaphragm for the given operating temperature, now we should consider another factor which is a chemical compatibility. Each rubber has characteristic and certain compatibility with the services fluid. Thus it’s very important to choose diaphragm material that suits our services.

Below is general chemical compatibility for some services fluid (data taken from http://www.marcorubber.com).

Services Fluid Buna N / Nitrile (NBR) Fluorocarbon (FKM) / Viton Silicone (VMQ) Neoprene (CR)
Sea Water Excellent Excellent Excellent Good
Nitrogen / Air Excellent Excellent Excellent Excellent
Natural Gas Excellent Excellent Good Excellent
Hydraulic Fluid Excellent Excellent Good Good
Diesel Fuel Excellent Excellent Good Good
Other chemical Vendor to Advise Vendor to Advise Vendor to Advise Vendor to Advise
         

From the table above, Buna N or Nitrile (NBR) and Viton has compatibility with all general service fluid. Although like this, we should also consider the budget that we have. Below is the general cost of each rubber material (data taken from http://www.marcorubber.com).

  Buna N / Nitrile (NBR) Fluorocarbon (FKM) / Viton Silicone (VMQ) Neoprene (CR)
Cost $ $$$ $$ $

 

In general application, as long as the operating temperature is within the operating temperature of the diaphragm material, then it will be ok. Also as long as the diaphragm material selected is compatible with the fluid, it will be ok. The consideration of mechanical properties isn’t a big issue since the pressure regulator valves usually operate at low ANSI class such as 150# and 300#. The vendors usually also already take into consideration regarding this operating pressure. For high pressure application, we shall consult the vendor to provide the suitable design and material.

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