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Instruction Manual
D103799X012
Principle of Operation
685SE and 685SR piston actuators utilize a 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. A bias spring that is either below or above the piston, depending on construction, will retract or extend the
piston rod upon a loss of supply pressure. This fail action will result in forcing an attached control valve to either
failopen or failclosed.
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 or hydraulic hand-pump 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 handwheel 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
handwheel manual override function to reposition the control valve even if the actuator cylinder or piston is removed
for maintenance. The hydraulic hand-pump override utilizes a hydraulic cylinder that is connected to the piston rod,
which is controlled by a manual hand-pump.
Table 2. Standard Constructions
PISTON
ACTUATOR
DIAMETER
SIZE
mm
Inch
10
254
10
12
305
12
14
356
14
16
406
16
18
457
18
20
508
20
22
559
22
24
610
24
26
660
26
28
711
28
1. Consult your
Emerson sales office
(1)
PISTON ROD
PISTON AREA
2
mm
Inch
cm
16
2.41
507
16
2.41
730
32
4.91
993
32
4.91
1297
32
4.91
1642
46
7.07
2027
46
7.07
2452
62
9.62
2919
62
9.62
3425
62
9.62
3973
or Local Business Partner for additional sizes.
VALVE STEM
CONNECTOR SIZE
2
Inch
mm
Inch
19
3/4
25
1
79
32 or 51 1-1/4 or 2 127 or 178 5H or 7
19
3/4
25
1
113
32 or 51 1-1/4 or 2 127 or 178 5H or 7
25
1
154
32 or 51 1-1/4 or 2 127 or 178 5H or 7
25
1
201
32 or 51 1-1/4 or 2 127 or 178 5H or 7
25
1
254
32 or 51 1-1/4 or 2 127 or 178 5H or 7
25
1
314
32 or 51 1-1/4 or 2 127 or 178 5H or 7
25
1
380
32 or 51 1-1/4 or 2 127 or 178 5H or 7
25
1
452
32 or 51 1-1/4 or 2 127 or 178 5H or 7
25
1
531
32 or 51 1-1/4 or 2 127 or 178 5H or 7
25
1
616
32 or 51 1-1/4 or 2 127 or 178 5H or 7
685SE/685SR Piston Actuator
VALVE TRAVEL
YOKE BOSS
DIAMETER
Minimum
mm
Inch
mm
Inch
90
3-9/16
25
127
5
25
25
90
3-9/16
25
127
5
25
25
127
5
25
25
127
5
25
25
127
5
25
25
127
5
25
25
127
5
25
25
127
5
25
25
127
5
25
25
127
5
25
25
June 2017
Maximum
mm
Inch
1
203
8
1
203
8
1
610
24
1
154
6
1
203
8
1
610
24
1
203
8
1
610
24
1
203
8
1
610
24
1
203
8
1
610
24
1
203
8
1
610
24
1
203
8
1
610
24
1
203
8
1
610
24
1
203
8
1
610
24
1
203
8
1
610
24
3
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