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
36
19) If main power was lost to trip the accumulator it will be necessary to log back in as the Admin
user so that the accumulator pressure transmitter readings can be observed on the HMI.
20) Increase the Accumulator Setpoint on the home screen of the HMI by 50 psi above the previous
setting.
21) Repeat steps 12 through 20, each time raising the Accumulator Setpoint by 50 psi. Continue this
process of triggering an accumulator fail, adding hydraulic fluid, and raising the Accumulator
Setpoint until the Accumulator Setpoint is equal to the Accumulator Recharge Pressure listed on
the actuator specification sheet.
This process of multiple recharges purges the accumulator/reservoir system of air. If this purging
process is not performed the system may cavitate, fail to achieve desired recharge pressure, or
continuously run after an accumulator recharge
5-9 Safe Seat System
With some valve types a plug or gate seats against a hard stop. Applying excessive actuator force while in
the seated position can permanently deform the seating surface, which may lead to process fluid leak by.
Seating valves with a force/thrust sufficient to properly seat, but also not cause damage, requires the
ability to accurately measure and control the actuator output.
With electro-hydraulic actuators, the actuator motor/pump initially continues running as the plug or gate
contacts the seat. Since the actuator piston is prevented from moving by the valve seat it is unable to
reposition in response to the rapidly increasing pressure in the cylinder caused by the running
motor/pump. This spike in actuator cylinder pressure occurs so quickly, within fractions of a second, that
it becomes extremely difficult to obtain, and maintain, an accurate seat load based on the valve position
only. In addition, thermal expansion and contraction of the valve and actuator assembly will affect the
seat load and must be continuously monitored and accounted for while the valve is seated.
To eliminate this problem, the Safe Seat system consisting of a Seat Load Accumulator (SLA) and pressure
switch, is employed. The SLA is a small displacement hydraulic accumulator installed in the actuator
system. It is preloaded with nitrogen (the exact pressure will vary) which initially keeps the SLA empty of
hydraulic fluid. When the plug or gate of the valve makes contact with the seat and the actuator cylinder
pressure begins to spike above the nitrogen pressure, the nitrogen is compressed, and the SLA starts to
fill with hydraulic fluid from the actuator system. Only as the nitrogen is compressed does the hydraulic
fluid pressure rise further. This slowing of the pressure rise allows the pump motor to change system
pressure over a greater length of time, thus allowing more accurate actuator pressure control.
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