Valve Maintenance

Gate Valve
  • Valve jammed when open
    • G M Engineering recommends that opened valves should not be jammed-tight on the backseat.
      Back-off a quarter turn from the fully opened position.
      Note that motor operated valves coast inevitably to the backseat by tripping on a limit switch. Valve should not be backseated on torque.
  • Valve jammed when closed
    • Variations in the temperature and/or pressure of the working fluid are often the cause of a valve failing to open. Thermal binding can occur in high temperature situations depending on the seat and wedge material, length of exposure and closing torque applied. Thermal binding can cause galling on the valve sealing surfaces as well as on the guides. A valve can lock in the closed position when high pressure enters the cavity and has no way to escape. This is known as over-pressurization.
      View technical note on thermal binding and over-pressurization
    • Is the valve operating temprature above 900 F?
      • Yes.
        • G M Engineering recommends the use of parallel slide valves for isolation at temperatures approaching 900°F. In the event that wedge gate valves have been selected, several precautionary measures are necessary to avoid thermal binding.
      • No.
        • Was the temerature difference equalized to within 75 F (24 C)?
          • Yes.
            • Is there a DCS override that is bypassing the open torque switch bypass?
              • Yes.
                • The factory setting allows the open torque switch to be by-passed for 5-10% of travel. This allows full boost power to open valve. Factory sizing is done to design conditions or available operating conditions. G M Engineering factory does not manipulate actuator manufacturer's settings. If valve is seeing much lower pressure differential, then close torque switch setting can be reduced. Please contact G M Engineering for more information.
              • No.
                • Does the valve have a warm-up bypass directly on the valve?
                  • Yes.
                    • Your valve problem will best be handled by contacting the G M Engineering Services Department. Please contact us at: valve@gmengg.com 91 281 2366034 Thank you for using the valve diagnostics system. As we are continually striving to improve customer service, we are interested in your feedback. Please send any comments or feedback to: valve@gmengg.com
                  • No.
                    • If there is no warm-up on the valve, time has been given for equalization and the torque switch settings cannot be reduced, please contact G M Engineering for further diagnostics.
          • No.
            • Typically a 12" valve takes 1.5-2 hrs to equalize on both sides to within 75°F. Check if the valve opens after equalization.
  • 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?