Blocking Plugs
Cherne Test-Ball and I-Series pneumatic blocking plugs for complete pipe isolation. Pressure testing, smoke testing, and construction shutoff. · 13 products
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About Blocking Plugs
When You Need a Complete Seal
A blocking plug stops all flow. No bypass, no bleed-through — the pipe is sealed. That’s what pressure testing, smoke testing, and construction isolation require: a reliable seal you can trust while your crew works or your gauges are reading.
Every blocking plug we carry is Cherne — the pneumatic plug that plumbing contractors and municipal crews have relied on for decades. Inflate to spec, verify the seal, and get to work.
Test-Ball vs. I-Series
Test-Ball — Single-size plugs. Each one fits a specific pipe diameter. The simplest, most proven design. If you know your pipe size and only work in one or two diameters regularly, Test-Ball is the straightforward choice.
I-Series — Multi-size range plugs. A single I-Series plug covers a range of pipe diameters, so one plug handles multiple sizes. Fewer plugs on the truck, more flexibility on-site. Better for crews that encounter varying pipe sizes across different jobs.
Blocking Plug vs. Bypass Plug
Blocking plugs create a complete seal — use these for pressure testing, air testing, and situations where zero flow is required. Bypass plugs (Muni-Ball) seal the pipe but divert flow through a channel — use those for sewer repair work where you can’t fully stop flow.
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Frequently asked questions
What is a pneumatic blocking plug?
A pneumatic blocking plug is an inflatable rubber plug that seals a pipe completely — zero flow. You insert it into the line and inflate it with a regulated air source until it expands tight against the pipe wall. Cherne® Test-Ball and I-Series plugs are the contractor standard for pressure testing, smoke testing, and construction isolation of sewer and drain lines.
How do you use a sewer test plug?
Insert the deflated plug through a manhole or clean-out and position it beyond the section being tested. Inflate to the pressure stamped on the plug using a hand pump or regulated air line, then verify the seal before pressurizing the line. Never stand in line with an inflated plug, and always deflate fully before removing it.
Can I use a test plug permanently?
No. Pneumatic plugs are temporary isolation tools — they hold for the duration of a test or repair, but gradual pressure loss and rubber degradation make them unsafe as a permanent seal. For permanent closure, use a mechanical cap or fitting rated for the application, and reserve your inflatable plugs for testing work.
What pressure can Test-Ball plugs handle?
Ratings vary by size and model — every Test-Ball and I-Series plug lists its maximum inflation pressure and maximum back pressure on the product page. Exceeding the inflation rating can burst the plug, so always use a regulated air source and verify the rating matches your test specification before inflating.
Should I use a blocking plug or a bypass plug?
Blocking if you need zero flow — pressure testing, smoke testing, construction isolation. Bypass if flow can't be fully stopped, such as repairs on an active sewer line: see our Muni-Ball bypass plugs. Never set a blocking plug in an active line without upstream diversion — backed-up flow builds dangerous head pressure behind the plug.
How much do pneumatic blocking plugs cost?
Our Cherne blocking plugs run from about $215 to just under $2,000, depending on pipe diameter and whether you choose a single-size Test-Ball or a multi-size I-Series plug. The lineup covers pipe from 4” to 24”; larger diameters and wider multi-size ranges sit at the top of the price range.