GE mn-28000_series Service Manual download pdf (Page 14)

14 | GE Oil & Gas

4.4 VARIPAK 28002 C

ADJUSTMENT

This adjustment is carried out by moving adjustment

knob (24) along adjustment plate (25) fastened to the

top of lever No. 1 (21). See section “Adjusting the C

of a Varipak 28002 valve for each plug and seat ring

combination”, page 7.

4.5 POSITIONER START-UP PRESSURE ADJUSTMENT

(Figures 7, 25, 26 and 27)

A. Connect the air supply and signal lines to the 7700P

or 7700E (with electrical signal) positioner.

B. Set the supply pressure according to the valve C

value (see the table in ﬁgure 3).

C. Set the signal to the minimum value for an Air-to-

Open actuator, and to the maximum value for an Air-

to-Close actuator. Turn take-up screw (116) until the

piston rod just begins to move. Tighten locknut (117).

5. Maintenance

Caution: Always ensure that there is no

pressure in the valve, actuator, or positioner

before maintenance or disassembly.

5.1 ACTUATOR DIAPHRAGM REMOVAL

(Figures 17, 24, 25, 26 and 27)

A. Unscrew the two pressure connection nuts (138a)

and pull tubing (140) out. Remove the four cap screws

(139) and diaphragm cover (137). Remove the worn

diaphragm. Form new diaphragm (136) and ﬁt it on

the piston as shown in ﬁgure 17. Fit the diaphragm

roll into the bracket groove. Take care not to twist

or bend the diaphragm during replacement. Reﬁt

diaphragm cover (137) with the four screws (139)

and reconnect the tubing with the two pressure

connection nuts (138a). Check that all connections

are leaktight.

Figure 17 - Diaphragm replacement

5.2 ADDING PACKING RING (Figures 18, 26 and 27)

A. Before adding packing ring, the valve must be

isolated and all pressure released. Remove packing

ﬂange nuts (8b), lift the packing ﬂange and follower,

and insert a new packing ring. Tighten nuts (8b)

ﬁnger tight and then tighten one full turn with the

wrench.

Figure 18 - Adding a packing ring

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GE mn-28000_series Service Manual Page 14

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