Here's a question I get all the time from plant buyers: "We're a Swagelok plant. If we bring in DK-Lok, are we going to have problems?" It's a fair worry. Nobody wants to be the person who saved a few dollars on fittings and then spent a weekend chasing leaks. After 20 years in the instrumentation valve and fitting business, here's how I walk folks through DK-Lok vs. Swagelok.
What's the Same
Both are two-ferrule compression tube fittings. A nut, a front ferrule, a back ferrule and a body. The front ferrule seals against the body and the tube, and the back ferrule grips the tube and drives the front ferrule. You make them up the same way: cut square, deburr, bottom the tube in the body, snug finger-tight, then pull up the turns the catalog calls for.
That means your techs don't need to learn anything new. Same tools, same habits, same inspection.
Can You Mix Them?
Yes. DK-Lok tube fittings are 100% interchangeable and intermixable with Swagelok and Parker A-Lok for like size and material, properly assembled per the DK-Lok catalog. In ASTM F1387 testing witnessed by TÜV Rheinland, 14 combinations of intermixed DK-Lok and Swagelok nuts, front ferrules, back ferrules and bodies, in 1/4" through 1" OD, went through proof, impulse, burst, vibration, thermal cycling and repeated assembly tests. Every combination passed, with "No failure observed," and DK-Lok backs it with a written intermix guarantee. See also the Parker A-Lok interchangeability letter.
Where Mixing Goes Wrong
When I see a leak on a mixed system, the brand is almost never the cause. It's one of these:
- Wrong size family. Metric and fractional fittings can look close on smaller sizes. A 6 mm part on 1/4" tube will not hold. Check the markings before you assemble.
- Mismatched material. Keep it like-for-like: 316 stainless with 316 stainless, brass with brass. The intermix guarantee covers same-size, same-material parts.
- Poor tube prep. An angled cut or a burr causes more leaks than anything else. Our tools page has RIDGID tube cutters made for stainless and deburring tools to get the end right.
- Under or over pull-up. Follow the DK-Lok catalog turns and check every first-time make-up with a gap inspection gauge. For tube sizes 1/4” OD and above, turn 1-1/4 turns from finger-tight. For tube sizes smaller than 1/4” OD, turn 3/4 turns from finger-tight.
At the bench, the Fitting Tool holds stainless steel tube fittings from 1/16" to 1/2" steady so you can keep both hands on the wrenches.
Leak Test What You Touched
Once the line is pressurized per your site procedure, apply Gator Leak Detector all the way around each joint you touched and watch for bubbles or foam. On male connectors and other NPT-to-tube fittings, check the pipe-thread joint as well as the tube nut, since the NPT side is often skipped. If something leaks, isolate and depressurize before putting a wrench on it. Never tighten a fitting under pressure.
So Which Should You Buy?
If your spec allows equivalents at a significant savings, DK-Lok gives you a fitting that intermixes with what's already installed, so you can repair or extend a Swagelok system without tearing it out.
Have a list of Swagelok or Parker part numbers? Our brand cross-reference page and our DK-Lok Southern California page are good places to start, or send the list over and we'll match it for you. A-Best Industrial Inc. Fittings, Valves, and Tubing is an authorized DK-Lok distributor and also supplies Swagelok and Parker when a project needs them.
We're Here to Help
Call A-Best Industrial Inc. Fittings, Valves, and Tubing at 310-833-3353 or email sales@abesttube.com. We're open Monday–Friday, 8:00 AM–5:00 PM Pacific, with after-hours emergency service.