Pump Motor Contactor

Hydraulic Fluid Heater

strainer, located in the reservoir, into the pump where it

is pressurized to 1400 psi and applied to the hydraulic

The fluid heater is a 175-watt immersion-type

pressure line. A fluid flow filter removes solid impurities

heater. The fluid must be kept at approximately 70F or

greater than 3 microns in size. In the event the filter

greater to prevent it from becoming too viscous and

becomes clogged, it is bypassed. The filter output then

causing servo errors. The heater is a Calrod type with a

flows past the pressure gauge, the pressure switch, and

built-in thermostat. The thermostat is normally factory

the bypass valve. The pressure gauge should indicate

set but may be adjusted if necessary. To adjust the heater,

1400 psi in normal operation, and the pressure switch

unscrew the cover plate by turning counterclockwise

should be closed for pressures above 1200 psi. The

and use the internal screwdriver adjustment to set the

bypass valve is normally closed and will open only if

temperature. It will take about a half hour for the tem-

the pressure exceeds 1800 psi.

perature to stabilize.

If the pump is operating normally, the bypass valve

will be closed and the fluid will flow through the check

Overtemperature Switch

valve and out the gate valve to the system. The check

valve is a one-way valve. The fluid returning from the

The overtemperature switch is a mechanically

system flows through the return gate valve and check

adjustable immersion-type thermoswitch. It is used to

valve into the reservoir. The return check valve only

indicate overheating of the pump oil. It does not indicate

allows fluid to flow in one direction and requires 75 psi

a direct failure. In a warm environment of approxi-

of pressure before it will open. This maintains the return

mately 85F the oil temperature will be about 120F. An

line pressure at 75 psi.

increase in oil temperature will most likely be due to

For the pump, heater, and overtemperature switch

increased fluid viscosity or a clogged pump falter. If this

to operate properly, the fluid reservoir must be properly

is the case, the pump should be drained and flushed with

filled. Too little fluid may actually cause the pump to

warm water, and the fluid and filter replaced.

overheat.

The overtemperature switch is adjusted by prying

the cap off the protruding stem and inserting a screw-

Pump Motor Contactor

driver in the stem.

The motor controller usually has 440 volts ac

Hydraulic Pressure Switch

applied to it. The pump is actuated by applying 115 volts

ac to the motor controller relay. The pump motor is

The hydraulic pressure switch is a single-pole,

protected by thermal overloads, located in the motor

double- throw, pressure-actuated switch. It is used to

controller. A thermal overload is a relay that is actuated

turn on the system electronics when there is enough

by heat. Motor current flows through a low-value

pressure to stabilize the system. It is normally set to

resists, generating a small amount of heat. If the current

actuate at 1200 psi.

increases beyond a specified value (3.7 amps), the heat

generated will melt a solder bond on a ratchet wheel,

The pressure switch is adjusted by turning the label

which holds back a spring-loaded relay. This will cut the

until the inner body is exposed. It can be turned with a

pump power by opening the circuit to the motor control

screwdriver or other instrument inserted in the inner

body holes. The pressure switch setting is decreased by

relay. The thermal relay should then be allowed to cool

turning the inner body counterclockwise as viewed from

before pushing the reset button on the pump controller.

the connector end.

The pump motor is factory wired for 440-volts ac

operation and should not be changed as the motor con-

The hydraulic pressure switch is a nonrepairable

item that must be replaced if it is not operating properly.

troller current limits are set for 440-volts ac operation.

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