How a Multi-Size Pipe Plug Holds Back a Sewer: Pressure, Area and Grip

English transcript

Transcript based on the published explainer script. Product specifications and selection guidance should be confirmed with Reliance.

This rubber plug weighs two and a half kilograms. Yet in a three-hundred-millimetre sewer, it can hold back a push of about seven hundred kilograms. So how does a rubber plug do that? Let's take it apart. Before you can inspect, repair or test a sewer, you need it isolated. But sewers don't stop. Flow keeps arriving from upstream. Push in a plug, inflate it, and the flow stops. But the water keeps building up behind it. That build-up is back pressure, and it pushes on every square centimetre of the plug. Here's the key idea. Force equals pressure times area. One bar is ten newtons on every square centimetre. A three-hundred-millimetre pipe has about seven hundred square centimetres of face. So one bar of back pressure pushes with about seven thousand newtons. That's roughly seven hundred kilograms. Now double the pipe diameter. The face area goes up four times, and so does the force at the same pressure. That's why larger plugs carry lower back-pressure ratings. From two bar on the smallest model, down to zero point two bar on the MS 600-1200. So what stops the plug from sliding? Grip. Inflate it, and the rubber presses outward against the pipe wall. That contact pressure, along the whole length of the plug, creates friction that resists the push. That's why the inflation pressure is higher than the back pressure it's rated for. On the MS 150-300, two bar inside, one bar behind. Two rules follow. Inflate to the rated pressure, using the gauge supplied with the plug. And never let the back pressure exceed the model's rating. Now the multi-size part. Folded, the MS 150-300 is only a hundred and thirty-five millimetres across, so it passes a hundred-and-fifty-millimetre opening. Inflated, its rubber and nylon body expands to seal pipes from DN150 all the way to DN300. One plug covers a whole range of pipe sizes. The standard line runs from MS 50-100 up to MS 600-1200. Each plug ships with a pressure gauge and a ten-metre air hose. Rubber and high-polymer nylon, vulcanized into one body. To choose one, start with three numbers. The pipe's measured inner diameter. The smallest opening the plug has to pass through. And the back pressure it has to hold. Pick the model whose range covers your pipe, and whose rating is above your working condition. Send us your pipe size and working conditions, and we'll match the plug.