GE mn-28000_series Service Manual download pdf (Page 12)

12 | GE Oil & Gas

VariPak valves are factory-calibrated according to

the components speciﬁed in the customer order. If for

any reason this calibration has been disturbed (e.g.

after changing from direct to reverse valve action, or

replacing the plug and seat ring), all or some of the

adjustments below must be carried out in the following

order:

- Piston rod clevis (104b) adjustment.

- Plug stem adjustment.

- Limit stop adjustment.

- C

adjustment.

- Positioner start-up pressure adjustment.

4.1 PISTON ROD CLEVIS ADJUSTMENT

4.1.1 Adjusting the piston rod clevis on the VariPak

28001 single-lever valve (Figures 14 and 26)

This adjustment is only required if the piston

(131) has been removed. In this case, it

should be carried out during reassembly,

before coupling the lever (113) to the clevises

(chap. MAINTENANCE - Reassembly. step H.,

page 17).

With the piston resting against diaphragm cover (137),

turn clevis (104b) so that the top of actuator bracket

(108) is 0.5 mm to 1 mm from the bottom of indicator

(126). A shim will simplify this operation. Admit enough

air pressure to disengage locknut (125) and tighten it

against indicator. Check that indicator (126) is correctly

positioned. Release air pressure.

4.1.2 Adjusting the piston rod clevis on the

Figure 14 - Piston rod clevis (104b) adjustment

VariPak 28002 adjustable-C

valve (Figures 14 and 27)

This adjustment is only required if the piston

(131) has been removed.

In this case, it should be carried out during

reassembly, before coupling the levers (21)

and (22) to the clevises (chap. MAINTENANCE

- Reassembly. step K., page 17).

With the piston resting against diaphragm cover (137),

turn clevis (104b) so that the top of the actuator bracket

(108) is 0.5 mm to 1 mm from the bottom of indicator

(126). A shim will simplify this operation.

Couple lever No. 2 (22) in this clevis position. Admit

enough air pressure to disengage locknut (125) and

tighten it against the indicator. Check that indicator

(126) is correctly positioned. Release air pressure.

4.2 PLUG STEM ADJUSTMENT

4.2.1 Adjusting the plug stem on the VariPak 28001

single-lever valve (Figures 15, 16 and 26)

This adjustment should be carried out during

reassembly, before coupling the lever (113) to

the clevises.

A. Loosen nut (103) and turn the plug stem using a

screwdriver while blocking clevis (104a) until the clevis is

in the position shown in ﬁgure 15. Lock nut (103).

Figure 15 - Presetting the plug stem position

4. Calibration

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GE mn-28000_series Service Manual Page 12

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