Baker Hughes Anti-Cavitation Control Valve with Variable Resistance Trim 79003 Series

- Inspection of the plug (12) and seat ring (21) seating surfaces must be accomplished to insure there are no scratches or dents.

- Repair of damaged surfaces should be performed by dressing the parts in a lathe to the angles shown in Figure 8. However no more than .015” (0,4 mm) of material should be removed to attain the desired angles. If one part requires dressing, it is recommended that both parts be machined.

- Note: Lapping of the plug and seat ring sealing surfaces is not recommended due to the close tolerance between the guide on the plug, and the presence of the stacked plate assembly and cage. Damage to the guiding surfaces could be incurred should any lapping compound work its way between them.

- The better solution consists in replacing all excessively worn or damaged parts by new parts if degree of tightness of these seating surfaces requires it.

If the seat ring seating surface is damaged, replace it according following to Section 9 “VALVE BODY ASSEMBLY”. In this case, it is recommended to install too a new plug-stem subassembly.

In order to get a higher tightness, the 79003 Series valves are equipped with a seat-ring with PTFE insert (“Soft-seat”) — see Figures 3 to 6. The assembly and disassembly operations of valve body does not present particular difficulties and must be achieved in the same order that hard seat valves.

- Meanwhile it is recommended to take supplementary precautions for the mounting of this special seat-ring in order to have it done in exceedingly clean conditions (total absence of foreign material).;

- Maintenance required on the stack plate assembly (19) is limited to inspection for any foreign objects being caught in the stack and insuring there are no burrs which could damage the plug guide. The stack is a one piece assembly and must not be disassembled.;

A. Removing Old Pin and Stem From the Plug

• Place the plug guide on a V-block, and using a drift punch, drive out the old pin.

Note: If it is necessary to drill out the pin, a drill bit some- what smaller than the pin should be used and the remain- der of the pin driven out.

• Hold the plug guide in a vise.

• Using a wrench applied on the two handling flats of the stem, unscrew the stem from the plug. The stem is removed by turning it anti-clockwise.

Refer to paragraph A of the above chapter “REPLACING PLUG AND STEM”. C. Drilling the New Stem

PIace the plug guide on a V-block and, using a suitable size drill bit, drill the stem using the hole in the plug as a guide.

Note: If the hole in the plug guide has been slightly dam- aged while removing of the old pin, choose a drill bit and a pin with a diameter somewhat larger than the normal pin.