Precision Orifices (Flow Restrictors) for Flow Control

color rendered model of cutaway customized precision orifices fitting example with thread by push-in connectionsMiniature precision orifices are widely used in flow control applications
 

Why use orifices or flow restrictors?
Precision orifices (flow restrictors) are highly adaptable, low cost and widely used components for controlling liquid, gas and air flow rates. They are vital for air and gas flow control. Because of this, it is important to have a general understanding of orifice design, function and selection. This post is an overview of miniature precision orifice features and materials plus some specific reasons for their usefulness in air and liquid flow control applications.

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What is an orifice?
An orifice or flow restrictor is a key component frequently found in air, gas and fluid flow control applications. At its simplest, it is a precision hole drilled through an otherwise solid surface that would block a flow stream. Here are some generalized uses for orifices:

 

  • Reduce flow
  • Increase air or fluid velocity
  • Precisely meter flow

By choosing a specific diameter, an orifice provides a cost-effective, reliable method to produce a predictable flow rate. This is why the phrase “precision orifice” is used when describing miniature flow restrictors. Providing reliable and predictable flow rates is an essential function of miniature precision orifices.


Orifice inserts and customization options
The use of orifice inserts to create custom fittings and connectors extends the usefulness of precision orifices by providing almost unlimited component variations, which expands design flexibility. The low weight and small size of orifice inserts make it possible to adapt precision orifices to an extensive range of air, gas and fluid flow application components.

In addition to standard orifice fittings, ISM carries thousands of plastic and metal fittings that can be retrofitted with precision orifice inserts. Customized fitting connection options include threaded, barbed and push-in, all available in configuration styles that include straight, elbow, tee and “Y” (wye). Because ISM can provide an immense selection of miniature orifice fittings, the only limits on application design are size constraints, component options and the designer’s imagination.

 

Customer’s Inquiry

We are looking for a flow restrictor with an elbow hose barb connection. We also need it to adapt to a tapered pipe thread port.

Concept


Hose barb elbow with threaded adapter and a precision orifice all in one part.

Components


Threaded elbow hose barb adapters are an off-the-shelf component as are brass orifice restrictors.

Finished Part

A finished part of a hose barb elbow with threaded adapter and a precision orifice.
A finished part incorporated each component into one precisely engineered part.

Learn more about ISM’s customized fittings and sub-assembly services
 

Miniature precision orifice uses
The applications and uses of miniature precision orifices are unusually extensive:

  • Precision flow control
  • Accurate timing in pneumatic and fluidic circuits
  • Pressure dividing circuits
  • Pneumatic resistance bridges
  • Speed control
  • Flow restriction
  • Accurate throttling
  • Ultrasonic sound sources
  • Precision metering of very low flow rates
  • Snubbers for gauges and instruments

The most frequent use of miniature precision orifices is providing reliably fixed and predictable flow metering in small-scale process and pilot plants. They are also widely used for metering additives to flow streams of any size. Choosing the best orifice for an application requires careful analysis of flow requirements as well as process conditions and the operating environment. Miniature precision orifices, especially orifice inserts, are so compact and lightweight that size is usually a minor consideration.


Orifice flow data
Generally, precision orifice flow data is proprietary and orifice choices usually include information on their flow data. This flow data is calibrated using idealized conditions and is dependent on the pressure difference across the orifice. Generally, flow data calculations are only good estimations, especially when air or gases are involved because of compressibility. It is usually necessary to obtain a range of orifice size samples for flow data analysis before choosing a final orifice size.

Some online resources for calculating flow data:


Why “precision” matters
Precision orifices get their name for a reason. They provide highly accurate and consistent flow rates. It is useful to understand what factors can influence this capability though. The choice of orifice material should be matched for chemical compatibility in order to prevent inaccuracy caused by corrosion, erosion and solids buildup. This is because the inside diameter of the orifice, its roundness, the length of the orifice throat and the condition of the orifice edges all affect flow rates through the orifice.


Process conditions and operating environment
Orifices are produced in a variety of materials to enable users to make the best match for operating conditions as well as for balancing value with durability. Precision orifices are usually available in plastic, metal and synthetic jewel materials.


Material options
Polymer (polysulfone and polycarbonate) orifices provide enhanced chemical compatibility and are especially cost effective. Brass or stainless steel is useful for higher pressure and temperature durability. Synthetic sapphire orifices are highly precise and suitable for high pressures and temperatures, plus they are especially resistant to erosion.

Download our Polysulfone Chemical Compatibility Chart


An Important Application Note
Any precision orifice will clog unless users provide adequate filtration just upstream of the orifice. Using a separate filter upstream of precision orifices will provide protective filtration that is easy to service. ISM’s precision orifice selection includes integrated filter precision orifice options.
 

In-line Filters for Miniature Flow Control Component Protection


Conclusion
Precision orifices are critical to an extensive variety of air, gas and fluid flow control applications. When used with suitable filter protection, they provide highly cost effective precise and reliable flow control. Material options and size ranges enhance their usefulness. The availability of precision orifice insert fitting customization provides users and designers with additional, almost unlimited, design flexibility.

Look for our next blog article when we will review some of the basics of the design and technical specifications of hose barb connectors:


Barb Connectors in Depth – Design and Function
 

Have you had some difficulty choosing the right miniature precision orifice for one of your projects? Did operating conditions or chemical compatibility cause problems? How about corrosion resistance or media temperature? Help us by telling others about what you learned.

Have questions about precision orifices features or function? If so, send me an email – steven.williams@industrialspec.com. You can also ask questions using the comments section below.

 

Steven C. Williams headshot March, 2018.

About the author
Steven C. Williams my LinkedIn profile link button.
Steven C. Williams, BS, is the technical writer and an inbound marketing specialist at Industrial Specialties Manufacturing (ISM), an ISO 9001-2015 supplier of miniature pneumatic, vacuum and fluid circuitry components to OEM's and distributors all over the world. He writes on technical topics related to miniature pneumatic and fluidic components as well as topics of general interest at ISM.       


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