- Excessive torque required to operate valve
Valve stem is improperly lubricated or damaged.
Disassemble the valve and inspect the stem. Acceptable deviation from theoretical centerline created by joining center points of the ends of the stem is 0.005"/ft of stem. Inspect the threads for any visible signs of damage. Small grooves less than 0.005" can be polished with an emory cloth. Contact G M Engineering if run-out is unacceptable or large grooves are discovered on the surface of the stem.
Valve packing compression is too tight.
Verify the packing bolt torque and adjust if necessary.
Foreign debris is trapped on threads and/or in the packing area. This is a common problem when valves are installed outdoors in sandy areas and area not cleaned before operating.
Always inspect threads and packing area for particle obstructions, even seemingly small amounts of sand trapped on the drive can completely stop large valves from cycling. The valve may stop abruptly when a cycle is attempted. With the line pressure removed from the valve, disconnect the actuator, gear operator or handwheel and inspect the drive nut, stem, bearings and yoke bushing. Contaminated parts should be cleaned with a lint-free cloth using alcohol, varsol or equivalent. All parts should be re-lubricated before re-assemble. If the valves are installed outdoors in a sandy area, it may be desirable to cover the valves with jackets.
Valve components are faulty or damaged.
If you suspect that the valve components are damaged or faulty contact G M Engineering.
The handwheel is too small.
Increasing the size of the handwheel will reduce the amount of torque required to operate the valve. If a larger handwheel is installed, the person operating the valve must be careful not to over-torque the valve when closing it.
- What bolt torque values are recommended for valves?
- What lubrication is recommended for threads?
- Is there a maintenance schedule for nuclear valves?
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