If you work in oil and gas, chemical processing, or any heavy industry where flow control is mission-critical, trunnion ball valves are likely the backbone of your operation. Unlike floating ball valves, where the sphere is held only by the stem, trunnion-mounted designs use two trunnion supports at either end of the ball, which means they handle higher pressure, larger line sizes, and more extreme temperatures without leaking or failing prematurely. As a supplier who’s sold, installed, and troubleshooted these valves for over a decade, I can tell you that 80% of the operational issues you’ll face aren’t hidden failures—they’re small, fixable problems that anyone with basic technical knowledge can diagnose and resolve. The key is approaching troubleshooting systematically, not guessing at parts or replacing components unnecessarily. Trunnion Ball Valve
Before we dive into step-by-step troubleshooting, let’s ground this in how trunnion ball valves work. The ball inside is held tight between two seats—usually made of PTFE, reinforced PTFE, or metal, depending on the service—and when the valve is closed, pressurized fluid pushes on the upstream seat to create a positive seal. Trunnion supports carry most of the pressure load, so the stem doesn’t get damaged from excessive thrust. That design, while robust, creates specific failure points that show up as common operational issues: leakage, inconsistent operation, or complete lockup. Let’s start with the most frequent problem first: leakage.
Most people assume leakage means a bad seal, but that’s not always the case. In fact, the number one cause of external or internal leakage on trunnion ball valves isn’t a worn seat—it’s improper installation or debris caught in the body cavity. I remember a refinery client who called us in a panic because a new line was leaking 10 gallons of crude oil per minute from the valve’s packing gland. We showed up on site, pulled out a basic socket set, and removed the packing gland bolts to find a tiny piece of welding slag from the line installation jammed between the packing and the stem. The installer had rushed through line preparation and skipped blowing out the line before connecting the valve, a mistake that cost the client $12,000 in lost product and unplanned downtime. That’s the first rule of troubleshooting trunnion valves: always rule out upstream or line-side issues before touching the valve itself.
So, step one for any leakage issue: isolate the valve safely. Never work on a pressurized or live line. Lockout/tagout (LOTO) procedures aren’t just a suggestion here—they’re non-negotiable. Once the valve is locked out, depressurize the body cavity by opening the drain ports on the bottom of the valve (almost every trunnion valve has these, a key feature that floating ball valves often lack). Letting the cavity drain is critical because trapped pressure can hold the ball slightly off-seat, causing leakage even if every other component is fine.
Next, distinguish between three types of leakage: external leakage (from the stem, body joints, or actuator mounting), upstream seat leakage (fluid leaking past the closed ball toward the upstream line), and downstream seat leakage (fluid leaking past the ball toward the downstream line). For external leakage, start with the packing gland. Loosen the packing gland bolts evenly—never loosen one all the way before the others, as that can warp the gland and create more leakage. If the leakage slows after loosening, that’s a sign the packing is compressed too tight, creating friction that damages the stem over time. If the leakage stays the same, the problem is either worn packing or debris in the stem. If you see a hissing sound when you operate the valve, that’s almost always trapped debris. In the case of the crude oil valve, that’s exactly what it was, but I’ve also seen this with process water, where sand particles from a new piping line get wedged into the packing.
For seat leakage, the next most common issue, start by checking the upstream and downstream line pressures. If the upstream pressure is much higher than the downstream, the ball is pushed firmly against the upstream seat, making that seat less likely to fail—it’s usually the downstream seat that leaks under pressure. If you test with a pressure gauge (we keep portable ones in our service vans for this exact reason), and you see pressure building on the downstream side when the valve is closed, that means the seat isn’t sealing. Again, check for debris first. Small, hard particles can scratch the seat or the ball, creating a path for fluid. If you’ve flushed the cavity and there’s still leakage, the next step is to check the seat’s orientation. Some trunnion valves have spring-loaded seats that need to face the correct direction to create the seal; during installation, it’s easy to flip a seat 180 degrees, which will make the valve leak immediately when pressurized. I’ve also seen clients use generic seats that don’t match the valve’s size or pressure rating—always use OEM or approved replacement parts, not off-the-shelf components, for trunnion valves. They’re engineered for specific thrust loads, and a cheap seat can crack under pressure.
The second most common problem we get calls about is inconsistent operation: the valve won’t open all the way, it sticks when operated, or it makes a grinding sound when the actuator cycles. This is almost always friction-related, and it usually happens because the valve isn’t being lubricated properly or the body cavity is full of trapped fluid or debris. Trunnion ball valves have a cavity between the two seats, and when the valve cycles open and closed, that cavity flushes with process fluid. If the process fluid is thick (like heavy oil, slurry, or sludge) or has solids in it, that fluid can harden in the cavity over time, locking the ball in place. We had a chemical plant client last year with a trunnion valve on a hydrochloric acid line that had been sitting in the closed position for six months during a plant shutdown. When they tried to open it, the actuator wouldn’t move at all. We isolated it, drained the cavity, and found a thick layer of salt deposits that had formed between the ball and the seats. Instead of replacing the valve, we used a mild acid flush (safe for the valve’s body material, which was carbon steel with a alloy coating) to dissolve the deposits, then cycled the valve slowly three times to work the remaining residue out. That saved them $30,000 in valve replacement and two days of downtime.
For inconsistent operation, start by checking the actuator output. If the actuator is pneumatic, make sure the air supply pressure is at the rated level—too low and it won’t generate enough force to turn the ball; too high and it can damage the stem or trunnion. If it’s electric, check the motor’s amperage draw; a spike when opening usually means friction or a blocked ball. Next, manually operate the valve (if it has a handwheel or override) to see if it moves freely. If it’s stiff, the issue is almost always in the body or trunnion assembly, not the actuator. We also recommend doing a periodic “dry cycle” on trunnion valves in static service—cycling them open and closed at least once a month, even if flow isn’t needed—to prevent that hardened build-up. For valves in slurry service, we usually recommend adding a flushing connection to the body cavity so operators can flush it with water or solvent during shutdowns, which is a simple modification that eliminates 90% of sticking issues.
The less common, but most severe, problem is complete lockup: the valve won’t open or closed at all, even after working on the actuator or flushing the cavity. This is almost always due to trunnion failure or seat wedging, usually from extreme pressure or improper operation. I’ve seen trunnion pins break when a valve was forced open while pressurized—operators sometimes crank on the handwheel too hard instead of checking the actuator, which puts unnecessary stress on the trunnion and the ball. If you suspect a broken trunnion, never try to force the valve open or closed—you’ll crack the body or snap the stem, which is a major safety hazard. Isolate the valve, depressurize it completely, and then carefully remove the actuator and the top of the valve body to inspect the trunnion. In most cases, a broken trunnion means the valve needs to be rebuilt, not replaced, as long as the body and ball aren’t damaged. We keep trunnion kits for all common valve sizes in our service stock, which means we can have a valve back online in 24 hours, instead of waiting weeks for a new unit.
A lot of clients ask us if there’s a way to prevent these issues, and the short answer is a regular maintenance schedule tailored to your specific service. Trunnion ball valves aren’t “set it and forget it” components, even though they’re designed for long life. For valves in severe service (high pressure, slurry, corrosive fluids), we recommend quarterly inspections: check the packing gland torque, cycle the valve, inspect for external leakage, and flush the body cavity. For valves in standard service, semi-annual inspections are sufficient. Another tip: when you install a new trunnion valve, mark the stem position with a paint dot so you can quickly tell if the valve has moved off its open/closed position during operation. That’s a quick check that can catch issues early, before they become serious problems.
If you’ve tried all these steps and still can’t diagnose the issue, or if you don’t have the technical expertise to work on the valve safely, don’t hesitate to reach out. As a trunnion ball valve supplier, we’ve worked with every type of industry and every type of valve issue, from small packing adjustments to full trunnion replacements, and we provide on-site troubleshooting and repair services that get your operation back up and running fast.
Centre-pivoted Butterfly Valve References
- ISA-75.08.01, Industrial Control Valves – Ball Valves, International Society of Automation, 2020.
- Trunnion-Mounted Ball Valves: Design, Operation, and Maintenance Guidelines, American Water Works Association, 2018.
- API 6D, Specification for Pipeline Valves, American Petroleum Institute, 2020.
- Process Valve Troubleshooting and Maintenance, Instrument Society of America, 2019.
- Trunnion Ball Valve Sealing Performance Under Dynamic Operating Conditions, Journal of Pressure Vessel Technology, Volume 142, Issue 3, 2020.
Zhejiang Sunawei Valve Co., Ltd.
As one of the most professional trunnion ball valve manufacturers and suppliers in China, we offer a wide range of valves with superior quality. Please feel free to wholesale high quality trunnion ball valve at competitive price from our factory. We also accept customized orders.
Address: Anfeng Industrial, Oubei Town, Wenzhou City, Zhejiang, China
E-mail: snv@sunawevalve.com
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