MTS Series 505G2 SilentFlo Hydraulic Power Unit Model 505G2-11 - Manual (Page 17)

Functional Description
Model 505G2.07/.11 SilentFlo™ HPU 17
Functional Description
Pump
A variable volume pump draws hydraulic fluid from the reservoir and pressurizes
it to the adjusted output pressure, typically 21 MPa (3000 psi). A check valve
prevents hydraulic fluid from being siphoned back into the reservoir. The
pressurized fluid is controlled by a control manifold that contains the high/low
pressure solenoid valve and a non-adjustable relief valve set at 22.4 MPa
(3250 psi).
Pressure
The start/low/high switch on the front panel of the electrical enclosure 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 is set at 22MPa (3190 psi) 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 front panel
signaling when the filter needs an element change.
Heat exchanger Hydraulic fluid temperature is maintained with a heat exchanger that cools the
fluid. The water-cooled heat exchanger cools the hydraulic fluid 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.
Note For additional information see the Heat Exchanger Care and Water
Quality Guide (part number 015-164-000).