Capping Off Tubing vs Plugging Off Ports - Photos, Video, PDFs

Tube fittings should seal and enable consistently tight-fitting installations. How do you choose between a cap and plug? We have tips, a video, and a free PDF that may help.

First, let's get oriented. Caps and plugs are types of tube fittings. Male connectors, crosses, adapters, reducers, unions, elbows, and tees are other types of tube fittings. Swagelok fittings are 1/16 to 2 in. in size with NPT, ISO/BSP, and SAE threads; constructed of 316 stainless steel, carbon steel, brass, 6-moly, or one of several alloys.

Installed properly, both caps and plugs can be pressurized so that you can fully pressure test a system to specifications.

Tube Cap

Use caps to cap off tubing.

A cap is a complete Swagelok assembly including nuts, front ferrule, back ferrule, and a fitting body. The fitting body is blank rather than open. This allows you to install the nuts and ferrules onto the tubing and pre-swage them onto the tubing. As with a regular tube fitting, it takes only one and 1/4 turns to pull it up into place. After installation, you can pressurize your system.

The video below in this post covers both assembly and reassembly. Additional information is on page 64 of the Tube Fittings catalogue (free download).

Tube plug

Use plugs to close off ports.

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 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.

The following video covers the difference between fitting caps and plugs and the most effective way to assemble each:

Click to play this demonstration video.

If you are planning an assembly and testing of a fluid system or subsystem, consider exploring what we offer. The Custom Solutions team at Swagelok Edmonton builds analytical subsystems, gas distribution systems, grab sampling systems, hose assemblies, regulator assemblies, and much more.

Consultation, fabrication, and pressure testing are included. Your assembly arrives ready to install, and is covered by the same warranty as our individual parts. We can advise on installation and maintenance too. 

Our testing capabilities add significant value for customers. We can leak test with hydro, pneumatic, and helium leak test equipment. We offer tighter testing tolerances than traditional leak tests — testing down to 1x10-6. No project is too large or too small, and even if the project has a short turnaround time, we may be able to assist.

We have posted a collection of free resources about fittings, as well. With the Tube Fitting Installation & Inspection Resource Collection, in one step you get our Installer's Pocket Guide for Swagelok Tube Fittings, how-to videos, the Fitting Installation & Troubleshooting Technical Briefing Video that goes more in-depth, and other information.

We have also posted at this blog about closely related topics, like how to choose fittings, ferrules, and tubing materials for your applications (in some cases materials should not match); how to apply PTFE tape to tapered pipe threads; and the advantages of adapter fittings.

Swagelok offers over 6,000 standard parts, and Swagelok Edmonton maintains over 10 million in local inventory. We have all the caps and plugs you need, along with a full range of other fluid system components. Please get in touch if we can answer any questions. Just click below and share a little information, or call 780-437-0640.