How to choose between pneumatic and mechanical pipe plugs: Four factors to consider

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 its inception nearly 70 years ago, the Cherne pipe plug offering has expanded to include testing, maintenance, and repair equipment for plumbing and municipal sewer markets in the United States. From humble beginnings, Cherne now offers two pipe plug types: pneumatic and mechanical, covering pipe sizes from .39 inches to 96 inches.

But the question remains: How do you decide between pneumatic and mechanical plugs?

Let's take a look at five questions or factors that will likely impact this decision.

• 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 I.D. (inside diameter). It's important to check the ID of the pipe to be plugged and match it to the usage range of the plug to make sure it will work in the intended pipe.
  • Pneumatic plugs come in sizes ranging from 1 inch to 96 inches and can be used for blocking (Test Ball), bypassing or redirecting effluent (Muni Ball), or conducting line acceptance or leak-location testing using air (Air-Loc Plug). Pneumatic plugs are designed to fit one pipe size or multiple pipe sizes.
  • Mechanical plugs are available in sizes ranging from .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 to be hand tightened. 
• What do you need the plug to do?
  • Pneumatic and mechanical plugs can be used for various purposes. To determine which Cherne plug to use, you have to nail down the purpose of the plug by asking:
    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, Cherne’s mechanical Aluminum T-Handle Gripper Plugs are available with or without a bypass and can be used for bypassing or air testing. 
• What is the point of access size into which you need to install the plug, and what is the maximum back pressure 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. Back pressure 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 back-pressure 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 back-pressure rating on the plugs to ensure the pressure you need to block does not exceed the plug’s capabilities.
• 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 over inflate or under-inflate Cherne 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 only require to be hand tightened.
    • 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.

To sum up: Once you have determined the ID of the pipe you need to plug, what you need the plug to do, the back pressure the plug needs to withstand, the media that needs to be blocked, and how long you need to keep the pipe plug in place, you can determine which Cherne plug to use based on your findings.

When in doubt, or if you have any questions about which plug is appropriate for your application, please call Cherne technical sales at 1-800-321-9532 / 1-800-THE PLUG