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Caps and Plugs: When to Use Which One?
by Katie Reid on Fri, Sep 06, 2019 @ 11:09 AM
They both block off parts of a fluid system and still fully pressurize it - so what's the difference?
Watch this Tech Tip video where we explain the difference between caps and plugs. (The video title emphasizes assembly instructions but it includes a review of when to use each one for your applications.) Also see our 2023 article "Capping Off Tubing vs Plugging Off Ports - Photos, Video, PDFs" for the latest information.
Caps
A cap is used to block off a piece of tubing at the end. With a cap installed, you can fully pressurize your system.
The cap is a complete Swagelok assembly, with a nut, a front ferrule, a back ferrule, and a fitting body. The difference is that the fitting body is blank rather than open. This allows you to install the nuts and ferrules onto the tubing and pre-swage them. As with a regular tube fitting, it takes only one and 1/4 turns to pull it up into place.
Later, when you want to switch out the cap, you simply remove the blank fitting body and follow standard Swagelok reassembly instructions to install the tubing into the rest of your fluid system.
Plugs
A plug is used to close off a port. If you have a tee, for instance, and want to use only two of the three ends, use a plug. You simply remove the nuts, ferrules and tubing, take the plug, and tighten it on the end you want to close off. The plug already has machined ferrules inside, so you don't need to pull it up 1 and 1/4 turns after it's finger tight. In this case, you tighten it only 1/4 turn, and the job is done.
As with the cap, a plug allows you to fully pressurize your system.
Edmonton Valve & Fitting has all the caps and plugs you need, along with a full range of other fluid system components (take a free Line Card here). Please see links below to more information and call us or message us if we can help:
Testing capabilities
We offer Custom Solutions services that include design, fabrication, and testing. We can leak test with hydro, pneumatic and helium leak test equipment -- with tighter testing tolerances (testing down to 1x10-6) than traditional leak tests.
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