Overview of Restriction Orifice Unions

Restriction orifice unions find use in a variety of fluid systems restricting the flow of liquid and gaseous process fluid. Restriction orifice unions can also be used to create a pressure drop or establish a back pressure in a piping system. The all-metal construction is designed to handle a wide range of pressures, temperatures, and fluids.

Within a restriction union is a replaceable orifice metering plate made from stainless steel. The plate slows down the flow of the process fluid, resulting in a drop in pressure from upstream to downstream. Keeping all factors (i.e., process fluid, pressure, and temperature) the same, changing out the plate for one with a larger or smaller orifice results in a greater or lesser flow rate, respectively.

The type of restriction orifice union manufactured by O’Keefe Controls Co. is called a single-stage restriction orifice union. The restriction orifice union consists of a pipe union within which is a plate with a bore. The bore (i.e. orifice) is specifically sized depending on intended pressure drop and a number of other fluid characteristics.

Typical Applications

Designed for use in a wide range of temperatures and pressures (up to 3000 psig), these devices find application in systems that process:

  • Chemicals
  • Compressed air
  • Coolants
  • Gases
  • Hydraulic fluids
  • Steam
  • Water



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Restriction Orifice Unions

Restriction Orifice Unions From O’Keefe Controls Co.

At O’Keefe Controls Co., we design and manufacture a broad selection of restriction union orifices.

Specifying Restriction Orifice Union

As an industry leader of fluid control products, we offer high quality restriction orifice unions with carbon steel or stainless steel construction. They are available in pipe sizes ranging from 1/4 inch to 2 inches and feature either socket weld or NPT (national pipe taper) connections. To determine the Restriction Orifice Union that best fits your application, simply select:

  • Orifice Size: Out to 3 decimal places in inches (Ex: .375” or 1.260”)
  • Pipe Size: ¼”, 3/8”, ½”, ¾”, 1”, 1-1/4”, 1-1/2”, 2”
  • Union Ends: NPT or Socket Weld
  • Union Material: A105 Carbon Steel or 316 Stainless Steel

PDF Restriction Orifice Unions Spec Sheet

Determining Bore (Orifice) Size

If orifice size is not known, our dedicated technical help support team can calculate proper bore size. In addition to the nominal pipe size, end connections, and union material, we require the following data:

  • Fluid Type (Air, Water, Steam, etc.)
  • Fluid Supply Pressure and Temperature
  • Pressure Differential Across Orifice
  • Required Flow Rate
  • Pipe ID or Pipe Schedule
  • Specific Gravity, if not air or water

Contact Us Today

At O’Keefe Controls Co., regardless of your flow control needs, we’re confident our stainless steel or carbon steel restriction orifice unions can meet your application requirements.

Contact us today for more information on our product offerings or to request a quote.