A ball valve is supposed to be the simple part of the system. Quarter turn, open or shut. So when one starts leaking or fights you on the handle, it's tempting to put a cheater bar on it and move on. A few minutes of troubleshooting first can save a snapped stem or a valve that won't isolate when you need it.
Start Safe
Follow your site's lockout/tagout procedure. Isolate the valve from both sides, bleed the trapped pressure in the body and the line, and verify zero before you loosen anything. A ball valve can hold pressure in the cavity even when both sides read zero, so bleed it with the handle partly open if your procedure allows.
Leaking Through: Valve Won't Shut Off
If flow gets past a closed valve, first check: is the handle fully at the stop? A bent handle or a loose handle nut can leave the ball a few degrees short of closed.
If it really is closed and still passing, the seats are usually damaged. The two most common causes are throttling (using the valve partly open to control flow) and debris like weld slag, tape shreds or scale that scored the ball or seats. Fix the cause, or the new valve will fail the same way. If you need to control flow, put in a needle valve and keep the ball valve for isolation.
Leaking at the Stem
A weep around the stem usually points to the stem packing or seals. Many instrument ball valves have an adjustable packing nut. With the valve depressurized, a small adjustment per the manufacturer's instructions often stops it. Over-tight packing makes the handle stiff and wears the seals faster. If adjusting doesn't fix it, replace the seals or the valve.
Hard to Turn
Valves that sit in one position for months can stiffen up from buildup on the ball, over-tight packing, or media that crystallizes or gums up inside. Don't force it with a pipe wrench or a cheater bar. Work it gently through its stroke a few times. If it stays stiff, plan to service or replace it, and add it to your routine exercise checks so it doesn't happen again.
On a line you service often, a swing-out style ball valve lets you swing the center body out to replace seats and seals without breaking the end connections.
Leaking at the End Connections
Many "valve leaks" are fitting leaks. On NPT ends, look for old tape, galled threads or a port that was over-tightened. On tube fitting ends, check that the tube was cut square, deburred, bottomed and pulled up per the manufacturer's instructions. If you remake it, the GRIP-IT TOOL, a deburring tool and a gap inspection gauge from our tools page make the job cleaner.
Replacing a valve on an existing Swagelok or Parker system? DK-Lok tube fittings are 100% interchangeable and intermixable with Swagelok and Parker A-Lok. 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." See the ASTM F1387 test report and the Parker A-Lok interchangeability letter.
Leak Test Before You Walk Away
Once the line is pressurized per your site procedure, apply Gator Leak Detector all the way around every joint you touched, including the stem and packing nut. On male connectors and other NPT-to-tube fittings, check the pipe-thread joint as well as the tube nut, since the NPT side often gets skipped. Watch for bubbles or foam. If something leaks, isolate and depressurize before putting a wrench on it. Never tighten a fitting under pressure.
Repair or Replace?
If the body is corroded, the stem is damaged, or a repair kit isn't available, replace it. When you do, match the pressure and temperature rating, seat material and end connections to the service, not just to what was there before. Browse our ball and plug valves collection.
We're Here to Help
Not sure whether to rebuild or replace? 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.