MEA INC
2600 American Lane | Elk Grove Village, IL 60007 | USA
T +1 847 766 9040 | F +1 847 350 1951
COMPLETE CONTROL
www.meaincorporated.com
MEA Incorporated | Hawk Actuator Instruction and Operation Manual
02/2018
32
5-6 Accumulator/Reservoir System
An accumulator system is used as an energy storage device to drive the actuator to a failure position,
either Extend/Clockwise or Retract/Counter-Clockwise, and may be initiated by a loss of control signal or
by one of two power losses: Loss of Main Power or Loss of Emergency Shutdown (ESD) Power. An
accumulator system is used in lieu of a spring where a spring would be impractical due to actuator
thrust/torque constraints.
The accumulator system consists of four main components: accumulator, reservoir, solenoids, and
pressure transducer. Both the accumulator and reservoir bottles have two sections divided by a sealed
piston, one section is filled with hydraulic fluid while the other is filled with nitrogen. The exact volume
and pressure of the hydraulic fluid and nitrogen differs by valve/actuator combination. Under normal
operation the accumulator will be filled with pressurized hydraulic fluid while the reservoir is nearly empty.
When an accumulator is tripped, two failure solenoids open simultaneously. The first solenoid is located
in a hydraulic tubing line connecting the accumulator and the actuator cylinder. The desired failure
position, Extend/Clockwise or Retract/Counter-Clockwise, will determine which side of the actuator
cylinder this tubing is connected to. Opening of this solenoid allows the pressurized hydraulic fluid in the
accumulator to be released and enter the actuator cylinder, driving the cylinder piston into the desired
failure position. Simultaneously, a second solenoid, located in a hydraulic tubing line connecting the
reservoir and the opposite side of the actuator cylinder, opens. Opening of this solenoid allows hydraulic
fluid to be pushed from the opposite side of the cylinder into the reservoir.
After an accumulator trip, or when power is restored, a pressure transducer indicates to the control
electronics of a low pressure condition in the accumulator and that a recharge is required before the
actuator can be returned to normal operation. In the interest of safety, the recharge process will only
initiate after the actuator is placed into Control mode. As the actuator cylinder piston is already at the
end of its travel and can move no further, running the motor/pump will draw hydraulic fluid from the now
filled reservoir and refill the empty accumulator. When the pressure transducer informs the control
electronics that the proper accumulator recharge pressure has been attained, both failure solenoids are
closed and the motor/pump stops running. Normal operation will then resume and the actuator will
travel to the control signal target position.
Note: The actuator is not available for control until completion of the recharge cycle. For Small, Medium,
and Large HPS units the duration of the recharge cycle is roughly equal to the 1.5 times the normal stroke
time of the actuator. For XL, Mega and Mega XL units, the larger, second pump does not run during the
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