Problems will arise to control valves in the course of time, because of the regular use. Of course, there will be problems that may be repaired without shutting down the system if it is not harmful. If in a dangerous position the valve repair must be done in the shop or the system is shut down.
This journal deals with a different problem arises with different types of control valves:
Plug Valve:
-
If leakage happens, the cause may be fluctuations in heat load and pressure. Depressurize the trapped fluid in the area, then tighten the cap bonnet cap to the specified torque.
-
If it still leaks, the valve needs to be repaired in the shop. If a leak occurs in the shaft and bonnet cap, the main cause is a poor sealing system between the valve and the seat. Check for possible wear damage to the inner diameter or consolidation of the packing or diaphragm.
-
If you use an O-ring gasket, replace it to stop leakage. If it still leaks,replacese the soft components (gaskets, etc.) with new ones. Bolt tightening can improve the sealing valve capability.
-
If a leak occurs at the flange connection, tighten the bolt in a transverse (criss-cross) manner. If it still leaks, it’s possible the surface of the flange gasket is damaged or the gasket needs to be replaced.
Ball Valve:
-
Leaks can occur at end connections (split connection), split body connections and between bonnet cap and body.
-
If a leak occurs at the flange connection, tighten the bolt in a criss-cross manner, if it still leaks, the flange gasket surface may be damaged or the gasket needs to be replaced.
-
If leakage occurs at a split-body connection, it is generally caused by unbalanced compression forces on the piping. Check whether the piping support guarantees the position of the pipe in a straight position. Then tighten the bolts on the split-body. If leakage still occurs, the gasket or surface has been damaged and needs to be replaced.
-
Check for leaks that occur between the bonnet cap and the body. If this happens, the cause may be fluctuations in heat load and pressure. Depressurize the trapped fluid in the area, then tighten the cap bonnet cap to the specified torque. If it’s still leaking, disassemble the valve and inspect the surface.
-
If a leak occurs in the shaft and bonnet cap, the main cause is a poor sealing system between valve and valve. Check for possible wear damage to the inner diameter or consolidation on the packing.
Butterfly Valve:
-
Correct operation and periodic troubleshooting of the butterfly valve can extend the service life.
-
Leakage on piping flanges is caused by misaligned piping (misalignment) or failure of the flange gasket. The body that is coated (linning) with rubber or elastomer will have a low impermeability if paired with a gasket.
-
The use of packing of graphite material, if operated at high temperatures will cause valve movements that are not smooth (jerky). For moderate levels this is under normal conditions.
-
Disturbances that often occur in the butterfly valve are leakage in (fluid through the valve) outside the provisions (in accordance with the valve class) caused by the seat. If a leak occurs before the age limit of the seat, it may be caused by damage to the seat or valve (disc).
-
Damage can be caused by erosion, mechanical failure of the seat, wearing due to friction between the seat and disc, or cavitation on the disc. Misaligment between the shaft and disc will also cause damage to the seat. Galling damage to the shaft will also inhibit the disc shift in full (the disc does not touch the seat)
-
External leakage also often occurs in the packing box. If the bolt tightening cannot stop the leak, it is likely that the packing has been damaged due to consolidation or extrusion.
Globe Valve:
-
Check for outside leaks that occur at the end-connection, the gap between the bonnet flange and body plug, the upper side of the packing box where the shaft comes out of the bonnet or other parts that receive high pressure.
-
Generally outside leaks can be stopped by tightening the bolt to increase compression pressure. If a leak still occurs after the tightening process, there is a gasket or packing that fails / is damaged and needs to be replaced
-
Inner leaks that occur before exceeding the life of the seat, generally caused by damage to wear between the seat ring-valve.
-
If damage occurs the first time you start up, chances are the surface of the seating has been damaged due to foreign matter
-
If a leak occurs after service, it is generally caused by misaligment between the seat and valve. During service, the process of laping between the seat and valve must be carried out perfectly to prevent the emergence of a gap that will cause leakage.
-
Disturbances in valve movement are caused by operations that are out of order. High temperatures will cause thermal expansion and increase friction. Pressure above the provisions will also cause the valve to be difficult to close.