Excess Flow Shut-Off Valves

Diffusion-Resistant, Diaphragm Seal, Excess Flow Shut-off Valves (FS Series)

FS Series Excess Flow Shut-Off Valves are designed to automatically shut-off the delivery of gas in a line if the flow exceeds a preset limit. They are commonly used as a safety device to protect a system from excess flow in the event of equipment failure or to protect personnel and property in the event of a line rupture. The capability of operating from 10 to 3500 psi allows them to be used either in high or low pressure applications.

The Excess Flow Limit Valve is a 2-position valve. In the “Open (Reset)” position, the valve provides a direct passage from inlet to outlet. In the other position, “Auto Shut-Off”, the valve is set to sense the flow and automatically shuts off the passage if the flow exceeds a preset value (flow limit). The valve will stay shut-off until it has been reset.

Six flow ranges are offered and the actual flow shut-off value for each range is dependent upon the operating pressure. The graph below indicates, for each range, the relationship between operating pressure and the actual flow limit. It is suggested that the range selected provide shut-off at 2-6 times the anticipated flow rate to allow for short term flow surges not connected with equipment failure.

Note: Piping systems, cylinders and other equipment can contribute rust or other particulate contamination that could cause the device to fail. Therefore it is highly recommended that all gases be filtered before they enter the FS Series Valve. See In-line Filters and Gas Line Filters for more information.

Standard Features

  • Type 316L stainless steel construction provides maximum corrosion resistance.
  • Elgiloy® diaphragm minimizes diffusion of air into valve and maintains gas purity.
  • High pressure design allows for use between a gas cylinder and the inlet to a pressure regulator.
  • Threaded holes on bottom of valve permit front panel mounting.

Optional Features

  • High purity inlet filter provides protection from particulate contamination.


  • Maximum Inlet Pressure 3500 psig
  • Minimum Inlet Pressure 10 psig
  • Differential Pressure at Flow Limit
    Ranges A , B, C and D: 5 psig
    Ranges E and F: 12 psig
  • Operating Temperture Range -10 °F to +150 °F
  • Inlet and Outlet Connections 1/4" NPT female
  • Approximate Weight 10 oz.
  • Surface Finish 15-20 Ra micro inch or less


  • Body Type 316L stainless steel bar stock
  • Bonnet Type 316L stainless steel
  • Seat PCTFE
  • Diaphragm Elgiloy® (or equivalent)
  • Spring Hastelloy C-22®
  • Other Metal Parts Exposed to Gas Type 316L stainless steel

Ordering Information

Part NumberNominal Flow Limit Value for Nitrogen at 1000 psig InletNominal Flow Limit Valve for Nitrogen at 30 psig Inlet
PRSFS-A-1904.8 slpm0.4 slpm
PRSFS-B-1909.1 slpm1.7 slpm
PRSFS-C-19021.8 slpm3.9 slpm
PRSFS-D-19039.5 slpm9.0 slpm
PRSFS-E-19072.3 slpm14.4 slpm
PRSFS-F-190120.6 slpm22.5 slpm