Data Sheet

685SE and 685SR Actuators
D103791X012
Product Bulletin
61.2:685SE/685SR
September 2014
3
Figure 1. Fisher 685SE Piston Actuator
X0992
TIE RODS
CYLINDER
MOUNTING BOSSES
VALVE STEM CONNECTOR
YOKE
PISTON WEAR RING
PISTON QUAD SEAL
PISTON
PISTON ROD
BEARING ASSEMBLY
BEARING RETAINING RING
PRESSURE CONNECTIONS
(TOP AND BOTTOM)
SPRING
SPRING CARTRIDGE
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 fail-open or fail-closed.
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,
anddecreasingitontheother.Thismovesthepiston
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 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.