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Web Exclusive: Small orifices for accurate flow control – sponsored by O’Keefe Controls Co.

Small orifices

Gas or liquid “flow rate” can be established using orifices of the proper size. Using accurately made orifices correspondingly accurate flow rate can be achieved. Small orifices (0.0003 - 0.125 in.) are required in many instruments and controls. A few generic applications include time delays in pneumatic circuits, filling or venting flow rate control, gas or liquid proportioning for mixing fluids, pressure pulse suppression (snubbers), bridge circuits for detection of minute flow rate changes, etc.

O’Keefe Controls Co. produces orifice assemblies in a variety of flow sizes, connection types and construction materials. Additionally measured flow rate charts for gases and liquids are provided for orifice sizes from 0.0003 to 0.125 in. More than 20,000 unique orifice assembly variations are available in both inch and metric standard dimensions.

For O’Keefe Controls website click here.

1. Synthetic sapphire orifices are mounted within a variety of plastic or metal bodies. Pipe threads, barb connectors and tubing connections allow for easy connection to standard control system fittings and manifolds. Click here for sapphire orifices.

2. All Metal Orifices are available in brass or stainless steel. The orifice is an integral part of the fitting and can be connected to pipe threads, plastic tubing, metal tubing or straight threads. Click here for metal orifice assemblies.

3. Flow Tables of Measured Flow Rates of both air and water are included in the website. Flow rate for orifices from 0.004 - 0.125 in. diameter are presented for pressure ranges from 1 to 100 psig.

Flow table section
Select figure to view flow tables.

4. Orifice Sizes Ranging From 0.0003 to 0.006 are termed “Micro-Orifices” and are used to establish very low flow rates of gases. A separate flow rate table is included on the website for these low flow products. Click here to view details on “Micro-Orifices.”

5. For Flow Rates requiring piping sizes from 1/4 to 2 in., orifice assemblies called “restriction orifice unions” are included on the website. Available materials of restrictions are carbon steel or stainless steel. Click here to view “Restriction Orifice Unions.”


6. Fixed Flow Rate Orifices provide a steady water flow rate for the pressure range from 15 to 150 psig. As pressure varies the orifice compensates and maintains the flow rate constant. Click here to view details on constant flow orifices.

7. Helpful engineering information is included on the website which provides information on how to compensate for:

  • Pressure levels beyond the range of the flow rate tables
  • Temperature conditions other than flow chart 70o F
  • Specific gravity other than that of air or water

Click here to view “Engineering Information.”

8. The concept of “choked flow of gases” is addressed in simple understandable language. This concept is often misunderstood. Click here to access flow rate discussion on “choked flow.”

Choked flow