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Swagelok Bangalore

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Diaphragm regulators vs Piston Sensing Regulators

Regulators are available in a variety of types, designs and materials of construction. There are three main categories of pressure regulators, including pressure reducing, back pressure and vaporizing. Within each of these three classifications, one can choose between piston and diaphragm regulators, and between one- and two-stage regulators. The below table shows what is the difference between diaphragm regulators vs piston sensing regulators.

 Diaphragm Regulators Piston Sensing Regulators


  • Generally the most sensitive in response to
    pressure changes, especially in low-pressure
  • Depending on their rating, they may be used with
    inlet pressures up to 248 bar and controlled
    outlet pressures up to 35 bar


  • Simple
  • Inexpensive
  • Sensitive
  • The diaphragm can be made from a variety of
    materials to provide increased compatibility with
    a wide range of fluids
  • Provides greater accuracy in sensing changes in
    outlet pressure


  • Diaphragms can be difficult to seal
  • Diaphragms don't usually provide a constant
    effective sensing area
  • Incases where there is a large pressure
    differential between the source pressure and set
    pressure, diaphragms can be susceptible to
  • Outlet pressure ranges may be limited to reduce
    the possibility of diaphragm rupture


  • Piston sensing mechanisms typically are used
    to regulate higher pressures than a diaphragm
    can withstand
  • Generally used in applications with outlet
    pressures higher than 35 bar, although they may
    also be suitable for lower pressures


  • More resistant to damage caused by pressure
    spikes and have a short stroke to maximize
    cycle life
  • The piston is contained by a shoulder in the
    regulator body cap to prevent piston blowout if
    the regulator outlet is over pressurized
  • The piston design has a constant effective
    sensing area which reduces droop


  • Least sensitive of the three traditional sensing
    element types
  • Can't be used in high purity applications due to
    O-ring seals
  • O-rings create the need for lubrication and raise
    the issues of fluid compatibility and possible
    system contamination

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