MTS Model 506-62-72 Hydraulic Power Supply - Manual (Page 38)

5-4 Theory of Operation
Pump motor When 1CR contacts close, the main pump motor starts, using a
Wye-delta start. First relay 1S energizes to close 1S contacts and
energize relay 2M (1M contacts close). Relays 2M and 1S provide a wye
connection (this reduces inrush current) to start the main pump motor.
After a timing delay that the PLC provides, output 105 energizes relay
2CR. The state of all 2CR contacts change to de-energize 1S and
energize 3M. Relays 2M and 3M connect the motor windings in a delta
configuration to provide full current to the motor. A set of 3M contacts
provides the motor status to the PLC at input 014.
High pressure When the HPS High/Low/Start switch is positioned to High, high
pressure is selected by energizing high-pressure solenoid 1 SOL for the
main pump.
Stop control When stop switch 1PB at PLC input 003 is pressed, the main pump
motor is turned off. The supercharge pump motor, however, continues to
run for approximately 10 seconds.
Emergency stop control Pressing Emergency Stop turns off the HPS by de-energizing relay CRM.
CRM contacts open to cut off power to the motor starter. The
supercharge pump may continue to run briefly while the main pump
winds down.
24 Vdc operation The HPS includes a 24 Vdc electrical power supply for operating
solenoid valves, relays and the PLC. Current available for external use
is listed in the specifications table. All solenoid valves connected to
this supply must be rated at 24 Vdc. If the 115 Vac control voltage
option is required, all solenoid valves connected to the supply must also
be rated at 115 Vac.