Instruction Manual
D103799X012
685SE/685SR Piston Actuator
September 2014
3
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.Thisfailactionwillresultinforcing an attached control valv e 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
(1)
ACTUATOR
SIZE
PISTON
DIAMETER
PISTON ROD PISTON AREA
VALVE STEM
CONNECTOR SIZE
YOKE BOSS
DIAMETER
VALVE TRAVEL
Minimum Maximum
mm Inch mm Inch cm
2
Inch
2
mm Inch mm Inch mm Inch mm Inch
10 254 10 16 2.41 507 79
19 3/4 90 3-9/16 25 1 203 8
25 1 127 5 25 1 203 8
32 or 51 1-1/4 or 2 127 or 178 5H or 7 25 1 610 24
12 305 12 16 2.41 730 113
19 3/4 90 3-9/16 25 1 154 6
25 1 127 5 25 1 203 8
32 or 51 1-1/4 or 2 127 or 178 5H or 7 25 1 610 24
14 356 14 32 4.91 993 154
25 1 127 5 25 1 203 8
32 or 51 1-1/4 or 2 127 or 178 5H or 7 25 1 610 24
16 406 16 32 4.91 1297 201
25 1 127 5 25 1 203 8
32 or 51 1-1/4 or 2 127 or 178 5H or 7 25 1 610 24
18 457 18 32 4.91 1642 254
25 1 127 5 25 1 203 8
32 or 51 1-1/4 or 2 127 or 178 5H or 7 25 1 610 24
20 508 20 46 7.07 2027 314
25 1 127 5 25 1 203 8
32 or 51 1-1/4 or 2 127 or 178 5H or 7 25 1 610 24
22 559 22 46 7.07 2452 380
25 1 127 5 25 1 203 8
32 or 51 1-1/4 or 2 127 or 178 5H or 7 25 1 610 24
24 610 24 62 9.62 2919 452
25 1 127 5 25 1 203 8
32 or 51 1-1/4 or 2 127 or 178 5H or 7 25 1 610 24
26 660 26 62 9.62 3425 531
25 1 127 5 25 1 203 8
32 or 51 1-1/4 or 2 127 or 178 5H or 7 25 1 610 24
28 711 28 62 9.62 3973 616
25 1 127 5 25 1 203 8
32 or 51 1-1/4 or 2 127 or 178 5H or 7 25 1 610 24
1. Consult your Emerson Process Management sales office for additional sizes.
(28 pages)
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