Friction Discussion - Emerson Fisher 657 Instruction Manual

Instruction Manual
D100306X012
5. Screw the valve stem locknuts up against the stem connector for the size 87 actuator. For all other actuator sizes,
screw the valve stem locknuts up until the indicator disk contacts the bottom of the stem connector. Do not
overtighten the locknuts.
6. Slowly stroke the valve from fully open to fully closed and verify full rated travel is achieved.
Be sure that the valve is in the closed position. Loosen the screws on the travel indicator scale (key 18), and align it with
the travel indicator disk (key 14) or stem connector for the size 87 actuator. Stroke the valve full travel to ensure that
the travel matches the rated travel on the nameplate. If valve travel is not correct, repeat the stem connector
procedure.

Friction Discussion

If you are attempting to adjust the bench set after the actuator is connected to the valve and the packing tightened,
you must take friction into account. Make the spring adjustment so full actuator travel occurs at the bench set values
(a) plus the friction force divided by the effective diaphragm area with increasing diaphragm pressure or (b) minus the
friction force divided by the effective diaphragm area with decreasing diaphragm pressure.
If the stem connector assembly has been installed, the valve friction may be determined by the following procedure:
1. Install a pressure gauge in the actuator loading pressure line that connects to the actuator diaphragm casing.
Note
Steps 2 and 4 require that you read and record the pressure shown on the pressure gauge.
2. Increase the actuator diaphragm pressure and read the diaphragm pressure as the actuator reaches a travel
position in the rated travel of the valve that does not contact a travel stop. Make a reference mark on the travel
indicator scale using tape or some other method at this point.
3. Increase the actuator diaphragm pressure until the actuator is at a travel position greater than the position
referenced in step 2 using the reference point to identify first movement.
4. Decrease the actuator diaphragm pressure and read the diaphragm pressure as the actuator returns to the position
referenced in step 2.
The difference between the two diaphragm pressure readings is the change in the diaphragm pressure required to
overcome the friction forces in the two directions of travel.
5. Calculate the actual friction force:
Refer to table 1 for the effective diaphragm area.
It is difficult to rotate the spring adjustor (key 74, figures 6, 7, 8, 9, and 10) when the full actuator loading pressure is
applied to the actuator. Release the actuator loading pressure before adjusting. Then re-apply loading pressure to
check the adjustment.
Note
For push‐down‐to‐close valves, the valve plug seat is the limit for downward travel and the actuator up‐stop is the limit for upward
(away from the valve) movement. For push‐down‐to‐open valves, the actuator down stop is the limit for downward movement,
and the valve seat is the limit for upward (away from the valve) movement.
Friction
Difference
Force, = 0.5
in pressure
pounds
readings, psig
657 Actuator (30/30i-70/70i and 87)
Effective

diaphragm area,
2
inches
June 2018
9