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Power Unit Operation:
This modular power unit provides electric-hydraulic power to extend and retract
the piston of one or more cylinders. Piston motion is utilized in various ways, such
as raising and lowering a tabletop, rotating a drum or garbage chute, and moving a
carriage (e.g. forks or platform). Piston motion is driven by a gear-type pump
directly coupled to an electric motor. Many components of the hydraulic system are
housed inside a manifold which is bolted to the gear pump. All components are
rated for 3,000psi working pressure.
1. Selector switch: for the hand control and dashboard pushbuttons to
operate, the selector switch must be turned to the ON position.
2. Hand control: connects to the power unit via a pigtail cord. The control has 2
buttons: UP and DOWN. The UP button causes the piston to extend. The
DOWN button allows the piston to retract.
• Extending the piston: Pressing the UP button activates the electric motor. The motor
turns the pump. As the pump rotates, oil is drawn from the reservoir, passes through
the suction filter, and enters the pump. The pump pushes oil through the check
valve and to the cylinder. As the cylinder fills with oil, the piston extends.
o Releasing the button turns off the motor. The piston maintains its position until
a control button is pressed.
o Limit switches (if included in the electrical circuit of your product) also shut off
the motor. See "Electric Circuit Diagram[s]" in the product owner's manual.
• Retracting the piston: Pressing the DOWN button activates the lowering solenoid valve. When the valve opens,
oil can bypass the check valve and flow to the reservoir (through return hoses). Oil flow to the reservoir is
regulated by the pressure compensated flow control valve. Regulating the volume of oil that can flow through
the spool, the piston retraction speed is kept constant.
o Releasing the button closes the lowering solenoid valve. The piston maintains its position until a control
button is pressed.
o Limit switches, if included in the electrical circuit of your product, also shut off the motor. (See Electric
Circuit Diagram(s) in your owner's manual).
3. Dashboard pushbuttons (2-Pushbuttons models only): the buttons are labeled "RAISE" and "LOWER". Pressing
the RAISE button causes the piston to extend. Pressing the LOWER button retracts the piston.
4. Electric motor: the motor (AC powered, i.e. plugs into a wall socket) is activated whenever the user presses a
button (up or down) on the hand control.
• AC-powered motors can be wired for either single-phase or three-phase operation. Regardless of phase
configuration, every motor is dual-voltage capable.
5. Pump: the pump shaft is directly coupled to the shaft of the electric motor. Several displacements are available to
match the horsepower of the motor.
6. Check valve: restricts oil flow to one direction through the circuit by preventing oil backflow through the pump to the
reservoir. Without a check valve, oil would return to the reservoir after the motor (and pump) stops. Oil can only
flow in response to an electrical signal from the hand control. This allows the piston to maintain any degree of
extension.
7. (Pressure) Relief valve: prevents system pressure from exceeding 3000psi. The valve opens a path for oil to follow
to the reservoir without traveling to the cylinder if pressure in the system exceeds 3,000psi.
8. Lowering solenoid valve: electrically-operated cartridge valve that activates when the DOWN button is pressed.
The valve has an integral screen to prevent contaminants from entering it.
9. Pressure compensated flow control spool: regulates the flow of oil to the reservoir when the lowering valve opens.
The spool is located beneath the lowering valve. It allows the piston to retract at a set, constant rate regardless of
the load applied (e.g. on the forks, platform, chute, tabletop, etc.). Several sizes are available.
10. Cylinder (not part of the modular power unit): the modular power unit controls movement of one or more
displacement style cylinders. As oil fills the cylinder, it pushes the piston out of the cylinder. Each cylinder includes
a bleeder valve at the top end. The valve allows air to be removed from the cylinder.
11. Velocity fuse: a safety device installed in the hose port of each cylinder. If a failure occurs that results in a sudden
loss of hydraulic pressure (e.g. punctured hose, leaking fitting or coupling), the velocity fuse automatically closes.
By closing, the fuse traps oil in the cylinder and prevents the piston from retracting. The piston remains stationary
until pressure is reapplied to the system.
NOTE: Air in the hydraulic system can also cause the velocity fuse to close even though no failure occurred.
To reset (open) the fuse, unload the work surface (forks, tabletop, chute, platform, etc.). Press and release the
UP button several times. Then, extend and retract the piston completely to purge air from the system.
12. Hydraulic fluid: HO150 hydraulic fluid. To replenish the fluid, add anti-wear hydraulic fluid with a viscosity grade
of 150 SUS at 100°F (ISO 32 @ 40°C) like AW-32 or Dexron transmission fluid.
Table of Contents
Rev. 11/27/2018
Copyright 2018 Vestil Manufacturing Co.
MPU-AC GEN2, MANUAL
MPU ASSEMBLY
RAISE
pushbutton
Selector
Switch
LOWER
push-
button
Cover
Dashboard
Lower lip
HAND
CONTROL
UP
DOWN
Page 18 of 23
Locking
pin
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