MTS Hydraulic Power Unit Model 506-92 - Manual (Page 6)

Introduction 1-2
1.1 Functional Description
Front panel controls
and indicators Front panel controls on the HPU include local operating controls and two
running time meters. Front panel indicators show power on, low oil
level, fluid over-temperature, motor overload and dirty filter conditions.
Pressure output The output pressure is controlled by an adjustment on the main pumps
and is monitored by the output pressure gage. An adjustable back-up
relief valve limits output pressure by porting fluid back to the reservoir
when the output pressure rises above the relief valve setting.
High/low pressure operation is controlled by the high/low solenoid
valves. These valves control the main pressure control (pressure
compensator) vent ports and the backup relief valve vent port.
Pressure
accumulation The pressure accumulator smoothes the HPU output pressure and
provides additional hydraulic flow for dynamic actuator demands. It is
precharged with dry nitrogen to a pressure proportional to HPU output
pressure. The slow turn-on accumulator slows the rate at which the
backup relief valve shifts from low to high pressure.
Temperature
control A temperature gage indicates hydraulic fluid temperature. An
oil-to-water heat exchanger controls the fluid temperature. When the
temperature exceeds a preset limit, a temperature sensitive switch turns off
the HPU and lights the front panel Over-Temperature indicator.
Fluid level indication A transparent gage indicates the level of hydraulic fluid in the HPU
reservoir. A low-level switch automatically turns off the HPU and lights
the front panel Low Oil Level indicator if hydraulic fluid drops below a
preset level.
Programmable logic
controller The PLC (programmable logic controller) located in the starter assembly
performs logic functions. The I/O (input/output) section of the PLC
provides an interface for various signals received from or sent to external
devices.
An optional module can be added to the PLC if remote control of the
HPU is required. This module provides the additional output indicators
needed for the remote control option.