The part that costs you the most on an instrument tubing repair usually isn't the fitting. It's the second trip back to the shop. A well-stocked truck, or a small shelf of spares near the plant floor, pays for itself the first time a line goes down on a Friday afternoon.
Here's what I'd keep on hand for the tubing and tube fitting work most techs run into.
Tubing in the Sizes You Actually Run
Carry the sizes that cover most of your plant, usually 1/4", 3/8" and 1/2" OD, in the wall thickness your fittings are set up for. Keep the ends capped and keep it off the floor of the truck bed where it can get dinged or pick up grit.
Coiled tubing is worth the space for longer runs and repairs where you want to avoid extra joints. Fewer fittings in a line means fewer places to leak. See what we stock on our tubing page.
Fittings: Fewer Part Numbers, More of Each
It's tempting to carry one of everything. In practice, a deep stock of a few fittings beats a thin stock of thirty. For most instrument work that means unions, male connectors, elbows, tees and caps and plugs in your main tube sizes, plus a handful of reducing fittings.
Keep spare nuts and ferrule sets too. When a ferrule gets dropped in the dirt or a nut gets galled, that small bag is the difference between finishing the job and chasing a part.
One note that makes stocking easier: 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. DK-Lok tested 14 combinations of intermixed DK-Lok and Swagelok nuts, ferrules and bodies in 1/4" through 1" OD to ASTM F1387-99(2005), witnessed by TÜV Rheinland, with the stated result "No failure observed." Read the ASTM F1387 test report and the Parker A-Lok interchangeability letter. So you can stock one brand and still work on whatever's already in the plant. Browse our compression tube fittings.
A Couple of Valves
A spare isolation ball valve and a needle valve in your common size can get a gauge or transmitter back in service the same day. If your plant runs a lot of gauges, add a gauge root valve.
Tools That Make the Repair Right
A clean, square cut and a properly deburred end are what keep a remade fitting from weeping. Keep a RIDGID tube cutter made for stainless, a deburring tool, a gap inspection gauge, and the right bender for your tube size. If you remake fittings often, a pre-swaging tool belongs in the box as well.
The GRIP-IT TOOL is the one most techs wish they'd had sooner. It locks onto stainless tubing while you cut with a tube cutter so the tube doesn't spin in your hand, and it fits 1/8", 1/4", 3/8", 1/2", 3/4" and 1" OD. For bench work, the Fitting Tool holds stainless steel tube fittings from 1/16" to 1/2" steady while you work on them. Both are on our tools page.
Sealant and Leak Detector
Keep thread sealant for the NPT side of your connections, and use one made for stainless so the threads don't gall. Tube ends never need sealant.
And don't leave without leak detector. 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 the one that usually gets skipped. If something leaks, isolate and depressurize before putting a wrench on it. Never tighten a fitting under pressure.
Keep It Stocked
A kit only works if it gets refilled. Write the part numbers and quantities on a card in the box, and reorder what you used before you put the truck away.
We're Here to Help
Want help building a kit that fits your plant? 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.