Diaphragm regulators vs Piston Sensing Regulators

Features

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

Advantages

• 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

Disadvantages

• 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
  rupture
• Outlet pressure ranges may be limited to reduce
  the possibility of diaphragm rupture

Features

• 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

Advantages

• 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

Disadvantages

• 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