MTS Series 505G2 SilentFlo Hydraulic Power Unit Model 505G2-30 - Manual (Page 17)

505.20/.30 HPU Functional Description
Model 505G2.20 - 505G2.30 SilentFlo™ HPU Introduction 17
Pressure
The start/low/high switch on the electrical enclosure’s front panel controls the
hydraulic pressure of the HPU. The start/low/high switch operates like an
automotive ignition switch; turn and hold the switch in the start position until the
motor starts running. The switch returns to the low position.
The unit automatically starts in low pressure to reduce the amperage needed for
starting, which will extend pump and motor life. When operating at this setting,
low-pressure fluid is available to the hydraulic circuit. Low pressure is achieved
by diverting a portion of the hydraulic fluid through the high pressure solenoid
and returning it to the reservoir. Selecting high pressure blocks the low pressure
return path and makes all of the pressurized hydraulic fluid available to the
hydraulic circuit.
The output pressure can be adjusted from about 1 MPa (145 psi) to 21 MPa (3000
psi). The HPU is designed to provide 21 MPa (3000 psi). A nonadjustable relief
valve set at 22 MPa (3190psi) to protect the hydraulic system from excessive
pressure.
Filtering As hydraulic fluid returns to the reservoir, it is filtered by a 3-micron element.
This ensures that all hydraulic fluid is filtered—whether it travels out through the
circuit or returns by way of the unit’s control manifold under low pressure.
Filter cleanliness is automatically monitored. An indicator lights on the unit’s
front panel signaling when the filter needs an element change.
Heat exchanger
A water-cooled heat exchanger is used to maintain the hydraulic fluid
temperature. The hydraulic fluid is cooled as it passes over water-filled plates. A
regulating valve monitors the temperature of the hydraulic fluid and adjusts the
flow of water through the plates. The flow of cooling water regulates the
temperature of the hydraulic fluid.
• The typical operating temperature range of the hydraulic fluid is
43–49°C (110–120°F).
• If the hydraulic fluid temperature exceeds 55ºC (131ºF), a switch opens and
shuts down the HPU.
• When the HPU is shut off, the flow of water is also stopped by a shutoff
solenoid valve.
For additional information, see the Heat Exchanger Care and Water Quality
Guide (part number 015-164-000).
Auto-Cooling Valve
(adjustable)
The auto-cooling function is integrated into the control manifold. During periods
of low flow demand from the external hydraulic circuit, this feature provides two
important benefits:
• Re-circulating flow that ensures hydraulic fluid filtering when the unit is on,
• Safeguarding against hydraulic fluid over-temperature.
The valve opens a hydraulic flow path through the fluid conditioning circuit
when external hydraulic demand for flow is low.
When the external demand increases, the valve closes the path to provide the full
flow of the HPU to the external demand.