Pneumatic vs. Mechanical Pipe Plugs

There are important factors to consider in choosing the best pipe plug for your application.

Pneumatic vs. Mechanical Pipe Plugs

Pneumatic pipe plugs are most often used for blocking, bypassing, conducting line acceptance or leak-location testing using air.

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In 1953, while working on an institutional job, Lloyd Cherne vulcanized a tire’s Schrader valve to a child’s inflatable rubber ball to create the first-ever pneumatic plumber’s test plug.

Since then, the use of both pneumatic and mechanical pipe plugs has expanded for plumbing and municipal sewer markets in the United States. Pipe plugs are used to stop or redirect the flow of wastewater during maintenance and testing in DWV (drain, waste and vent) and sewer systems. Many plugs are custom-made to suit the precise specifications required in a variety of applications, including emergency situations.

How do you decide between pneumatic and mechanical plugs? Let’s take a look at four questions or factors that will likely impact this decision.

1. What is the inside diameter of the pipe you need to plug?

The first step in choosing a pipe plug is determining the pipe’s inside diameter. It’s important to check the I.D. of the pipe to be plugged and match it to the usage range of the plug to make sure it will work properly.

Pneumatic plugs come in sizes ranging from 1 inch to 96 inches and can be used for blocking, bypassing or redirecting effluent, or conducting line acceptance or testing for leak location using air. Pneumatic plugs are designed to fit one pipe size or multiple pipe sizes.

Mechanical plugs are available in sizes ranging from 0.39 inch to 18 inches and do not need to be inflated. They are expanded to fit tightly within a pipe or open mechanically. Most only require hand-tightening.

2. What do you need the plug to do?

Pneumatic and mechanical plugs can be used for various purposes. To determine which plug to use, you have to nail down the purpose of the plug by asking the following:

Do I need to …

… block a pipeline or an opening?

… bypass effluent that is running through a live pipeline?

  pressure-test a new pipeline before placing it into service or test a pipeline already in service for leaks?

As mentioned above, pneumatic plugs are used for blocking, bypassing, conducting line acceptance or leak-location testing using air. Most mechanical plugs are designed for blocking. However, some plugs are available with or without a bypass and can be used for bypassing or air testing.  

3.  What is the point of access size into which you need to install the plug, and what is the maximum backpressure the plug must withstand?

The size of the point of access into which you need to install the plug will likely impact the plug needed for the job. Backpressure is the pressure (air or liquid) in front or back of the plug that it must restrain or hold back. It is important never to exceed the plug’s backpressure rating. 

The total force exerted on a pipeline plug is directly proportional to both the pressure and the pipeline area. It’s important to check the backpressure rating on the plugs to ensure the pressure you need to block does not exceed the plug’s capabilities.

4.  What media does the plug need to block and how long does it need to be kept in place?

The type of plug needed will depend on the media the plug needs to block; for example, air, water, sewage or something else. 

Pneumatic plugs:

  Pneumatic plugs are meant to be used in short-term applications. If a pneumatic plug needs to remain in place for longer periods, its inflation pressure must be checked every four hours and adjusted as required.

  Pneumatic plugs can be inflated with air, water or any inert gas (nitrogen). It’s crucial never to overinflate or under-inflate plugs.

  When pneumatic plugs are in use, for safety reasons, the work area has to be cordoned off so that nobody gets in front of the plug. For this reason, an extension hose must be used to inflate and deflate pneumatic plugs from a safe distance.

Mechanical plugs:

  Mechanical plugs do not need to be inflated. They are expanded to fit tightly within a pipe or open mechanically.

  Most mechanical plugs  require only hand- tightening.

  Mechanical plugs are the correct choice for long-term or permanent installations.

  Some offer specialized features such as chemical resistance, the ability to lock in place, or are designed for specific applications, such as pipe hubs and clean-out coverings. 

Jake Shevik is a product manager at Cherne. He can be reached at


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