MAINTENANCE

SERVICING THE VALVE SEATS

1. Remove housing assembly and bottom cap per instructions for servicing packers.
   
   
2. With packers still in place, remove the internal parts by unscrewing the piston from the disc. This is a right hand thread and should have been locked tightly. While it is possible to use an open end or adjustable wrench on each end of the disc/piston assembly, it may be more convenient to use a special disc wrench available from Valv-Trol. This wrench allows one end to be easily held by the studs or cap screws while you use a wrench on the other end.
   
   
3. Once the threads have disengaged, pull the piston and disc straight out of the body being careful not to nick any of the machined surfaces. The header ring and packer should pull out at this time also. Set aside the piston, disc, header rings, and packers for cleaning and inspection.
   
   
4. The seat ring is now the only part left to remove. If the seating surface appears to be in good condition, and if there is no evidence of leakage between the seat ring and the body, and if the seat ring is tight in the body, it may not need to be removed. If there is any question at all, it should be removed to check the machined surfaces.
   
   
5. To remove the seat ring, it is necessary to have a tool that will fit the milled slots in the seat ring and extend out of the body enough to receive a wrench or bar for turning. It is also desirable for the wrench to guide on the inside diameter of the seat ring, to help prevent slipping and damaging the seating surface. A special seat wrench is available from Valv-Trol for each size seat ring we offer.
   
   
6. The valve body must be held firmly to prevent rotation when removing or installing the seat ring.
   
   
7. Locate the wrench in the body and turn until the wrench lugs fall into the slots of the seat ring. Insert a 24” to 36” steel bar through the wrench hole, far enough to form a T-handle. Grab both ends of the bar and turn counter- clockwise. It may be necessary to use a longer bar if extra force is needed to break it loose.
   
   
8. Once the hardened seat ring is loose and unthreaded, pull it out of the body using care not to damage the machined body.
   
   
9. Now that the body assembly is completely apart, all parts should be cleaned thoroughly and inspected. Good machined surfaces and cleanliness are very important here for proper service life. There are basically seven machined surfaces that should be checked before reassembly. They are:
   
   (a) The land or shoulder in the body that contacts the seat ring.
   (b) The flat bottom of the seat ring.
   (c) The angled seating surface of the seat ring.
   (d) The angled or radiused seating surface of the disc.
   (e) The outside diameter of the disc and piston.
   (f) The inside diameter of the body where the packers seal
        (the stuffing box area).
   (g) The ends of the discs, pistons, or spacers.
   
   
10. Any parts repairs or replacements should be done now. The seat rings and discs can generally be remachined several times if damage is not too severe. We do not recommend remachining in the field. Valv-Trol has the facilities to properly bring these parts back to serviceable condition. We also have the knowledge of how much machining can be done without sacrificing the performance or service life of the valve. Valv-Trol offers this parts repair service at a very significant savings over new parts.
    
    
11. Marks on the outside diameter of the disc and piston can usually be polished out with fine emery cloth. Any major nicks or grooves may reduce the life of the new packers significantly, so replacement of the disc or piston may be best. Nicks or grooves in the packer area of the body can sometimes be removed by hand with fine emery cloth. The shoulder where the seat ring contacts the body must be perfectly flat and clean to form the proper seal. We recommend running a clean finger around this land, to wipe off all dirt or lint just before replacing the seat ring.
    
    
12. The seat ring can now be replaced. A lubricant is not needed, but if it is used on the threads, be sure not to allow any dirt or grit to be trapped between the mating surfaces. The seat ring should be tightened with the seat wrench and bar until it is locked tightly in the body. Pull evenly on both sides of the bar. It is nearly impossible to get the ring too tight or strip the threads on any but the smallest size (3/4”) valves. A proper fit here should result in the seat ring “snapping” tight in the body. “Mushiness” during final tightening may indicate dirt or burrs on the land. A tight seal here is important to long service life.
    
    
13. The next step is to lap the disc and seat ring together for a perfect metal to metal seal. We recommend using a 240 grit or finer abrasive lapping compound. A water based compound will generally be easier to clean up after you are done, but an oil based compound will work also. Refer to the lapping instructions for the proper techniques.
    
    
14. Once the lapping is complete, the disc and piston can be inserted in each end of the body and threaded together. We recommend using a light coating of anti-seize compound on the male end of the piston (thread and pilot, but not the face), to reduce the chance of galling.
    
    
15. Holding one end with the disc wrench, tighten the other end with a wrench until the disc and piston are firmly locked together. Use care to prevent turning the disc if it is in contact with the seat ring. A little extra care here will prevent galling or otherwise damaging the freshly lapped seating surfaces. “Mushiness” during final tightening may indicate dirt or burrs are preventing proper contact between parts. If so, disassemble and clean before reassembly.
    
    
16. Insert header rings and packers and reinstall the housing assembly and the bottom cap, per the instructions for servicing packers.
    
    
17. Your repair is now complete and the valve is ready to test and reinstall.