Edmonton Valve & Fitting Blog

Weekly posts for northern and central Alberta engineers, plant operators, and buyers.

Caps and Plugs: When to Use Which One?

by Luke Wurban, 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, and when to use each one for your applications.

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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.


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. 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. Call us at 780-437-0640 or contact us through our website.

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