Educational Services; Principle Of Operation - Fisher 685 Instruction Manual

Instruction Manual
D103626X012

Educational Services

For information on available courses for Fisher 685 piston actuators, as well as a variety of other products, contact:
Emerson Automation Solutions
Educational Services - Registration
Phone: 1-641-754-3771 or 1-800-338-8158
E-mail: education@emerson.com
emerson.com/fishervalvetraining

Principle of Operation

685 piston actuators utilize a pneumatically controlled piston that moves inside of a cylinder to generate thrust. A seal
contained on the circumference of the piston provides a seal between the piston and the cylinder, preventing supply
pressure leakage.
From an equilibrium state, the actuator operates by reacting to a force unbalance that is created by increasing supply
pressure on one side of the piston, and decreasing it on the other. This moves the piston up or down, and results in a
repositioning of the attached control valve. Travel can be adjusted using travel limits within a valve positioner, which
limit the travel range of the actuator. The optional handwheel manual override does not have the ability to act as a
hard travel stop.
An optional handwheel manual override is capable of extending or retracting the actuator manually and can be
engaged at any position from full open to full close. This override utilizes a worm gear assembly that is attached to the
stem connector and not attached to the cylinder or piston rod. This enables the manual override to reposition the
control valve even if the actuator cylinder or piston is removed for maintenance.
Table 2. Standard Constructions
ACTUATOR PISTON
SIZE DIAMETER
12 305
14 356
16 406
18 457
20 508
22 559
24 610
26 660
12 12
14 14
16 16
18 18
20 20
22 22
24 24
26 26
1. Consult your Emerson sales office or LocaL Business Partner for additional sizes.
(1)
PISTON ROD
PISTON AREA
AREA
mm (cm
16 730
32 993
32 1297
32 1642
46 2027
46 2452
62 2919
62 3425
Inches (inch
2.41 113
4.91 154
4.91 201
4.91 254
7.07 314
7.07 380
9.62 452
9.62 531
YOKE BOSS
VALVE STEM
DIAMETER
CONNECTOR SIZE
2
for Area)
32 or 51 127 or 178
32 or 51 127 or 178
32 or 51 127 or 178
32 or 51 127 or 178
32 or 51 127 or 178
32 or 51 127 or 178
32 or 51 127 or 178
32 or 51 127 or 178
2
for Area)
1-1/4 or 2 5H or 7
1-1/4 or 2 5H or 7
1-1/4 or 2 5H or 7
1-1/4 or 2 5H or 7
1-1/4 or 2 5H or 7
1-1/4 or 2 5H or 7
1-1/4 or 2 5H or 7
1-1/4 or 2 5H or 7
685 Piston Actuator
June 2017
VALVE TRAVEL
Minimum Maximum
>203 610
>203 610
>203 610
>203 610
25 610
25 610
25 610
25 610
>8 24
>8 24
>8 24
>8 24
1 24
1 24
1 24
1 24
3