Cherne muni ball

Bypassing Large Pipelines with Pneumatic Pipe Plugs – What You Need to Know

Pipe plugs are designed to perform three essential functions:

  1. Blocking a pipeline
  2. Conducting an air test in a pipeline
  3. Bypassing effluent in an active pipeline

Blocking a pipeline becomes necessary during new installation or maintenance when either effluent needs to be temporarily stopped or when a new pipe is being air tested for leaks.

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Air testing a pipeline is necessary when testing a new installation for leaks before placing it in service or when trying to locate a leak in an existing line.

Bypassing is necessary when the flow of effluent in a pipeline needs to be redirected, most commonly when maintenance or repair is required for a longer period of time when the flow cannot be stopped.
This article concerns sewage bypass, selecting and using bypass plugs, and plug safety guidelines. A bypass plug has a tube or hose open at both ends of the plug, which runs entirely through the plug.

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Bypass pipe plugs used in waterworks applications are pneumatic plugs. Pneumatic pipe plugs are used for blocking, bypassing or air testing. Mainly used when working with industrial underground waterworks systems, they can fit into pipes up to 120 in. in diameter. They can also be used in smaller plumbing applications to test a complete system for leaks.

A pneumatic pipe plug is a rubber ball that can be inflated with air, water or any inert gas (nitrogen) with a bicycle pump or large air compressor. As it fills with air, it expands against the pipe and seals in place, either stopping the flow in the pipe or redirecting it to go somewhere else. A second test ball must be put in place to check for any leaks between the two to run a low-pressure air test.

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Bypass/muni ball plugs are used for testing and monitoring pipe systems. Some bypass plugs are designed to handle high back pressure in applications such as water mains, force mains, and industrial lines. A Muni Ball has a bypass tube running through the plug that allows the user to bypass effluent through the tube.

Most bypass pipe plugs come with adapter caps threaded onto the bypass on the front of the plug. Those with caps can also be used for blocking and with the cap removed, they can be used for bypassing. And, with the cap adapted with air fittings, it can be used to perform an air test. There is a broad size range of bypass plugs on the market from ¾ to 96 in. in diameter, with bypass tubes ranging from ½ in. to 24 in.

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Types of Bypassing

Certain bypass pipe plugs are designed for two types of bypassing. Pump bypassing and gravity bypassing.

Pump Bypassing

Bypassing with a pump involves a municipal pipe plug being installed in a pipeline upstream from where maintenance or replacement work needs to be conducted. The plug is installed into the pipe, and a hose or pipe is attached to the bypass on the front of the plug. The hose is then connected to a pump on the intake side and another on the output side.

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pump bypassing diagram

Then, effluent is pumped up and out of the manhole running downstream, and past where the work is being conducted, before it is routed back into another manhole where the effluent can continue. A blocking plug is installed on the upstream side of this manhole to prevent effluent from flowing toward the work area.

Gravity Bypassing

This type of bypassing occurs when work needs to be conducted in an active manhole, but the flow cannot be blocked. In this instance, two municipal pipe plugs are installed into both access pipes that feed into the manhole. A hose is connected between the bypasses of the two plugs so that the flow can continue while the manhole remains dry.

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gravity bypassing

Proper Pipe Plug Selection

To select the correct municipal pipe plugs for your application, the following questions need to be answered:

  • What is the inside diameter of the pipe you need to plug?
  • How much volume must the bypass accommodate? This goes to the size of the bypass required. You can obtain this information from your project engineer.
  • What are the back pressure requirements? In other words, how much pressure will the plug be required to hold?
  • Pressure is most commonly measured by either pound per square inch (psi) when the pressure is coming from air, or
  • Feet of head, if the pressure comes from liquid such as water or sewage.
  • What is the access opening the plug needs to fit through to be installed? Most commonly, this would be the diameter of the manhole the plug must be passed through before it is installed. Many of municipal pipe plugs have flexible hose bypasses that allow the plug to be bent up to 45 degrees to aid in installation
  • What is the temperature of the media being blocked? Cherne’s Muni Balls are made of natural rubber because of their flexibility, memory, and durability. However, natural rubber should not be exposed to temperatures exceeding 125 degrees Fahrenheit, as it will begin to melt.
  • Are there going to be any oils, hydrocarbons, or petrochemicals in the media the plug needs to be blocked? These may harm natural rubber and cause it to degrade. Please consult with the factory if your application involves blocking substances such as these.

Important Safety Considerations

Special care needs to be taken before and after a Muni Ball or any pneumatic plug is placed into service:

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  • Inspect the rubber body of the plug for punctures, bulges, cracks, corrosion, and leaks.
  • Inspect the end plates of the plug for cracks, loose fit, missing or damaged eyebolts, rusty end plates and fittings, and damaged inflation fittings.
  • If any of these appear, we recommend consulting the Cherne factory.

While installing the Muni Ball:

  • Make sure an extension hose with an accurate pressure gauge is used to safely inflate the plug, monitor its air pressure while in use, and deflate the plug from a safe distance.
  • Always ensure the pipe the plug is being installed in is inspected and debris such as gravel or broken glass is removed.
  • Avoid installing the plug over any exposed rebar.
  • Ensure the plug is inflated to the exact inflation pressure prescribed by the manufacturer.

After the work is completed, eliminate any back pressure in the pipe before deflating the plug. Do not attempt to remove the plug from the pipeline until it has been completely deflated.

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Remember, most damage occurs to pipe plugs when they are either being installed or removed from the pipe. A safety instruction manual is provided with each Muni Ball when it leaves the factory. Make sure you review it and understand all precautions.

Pete Rogers is an inside sales specialist at Cherne Industries, part of the Oatey family of companies.

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