MTS Model 512-14 Hydraulic Power Unit - Manual (Page 8)

512.14 Hydraulic Power Unit 8
Functional Description
Introduction
Functional Description
The hydraulic power unit (HPU) is the mechanical source of high-pressure
hydraulic fluid required to operate the hydraulic components of a test system. See
“Component Identification” on page 6 for more information about the
components discussed in this section.
Pump A motor drives a hydraulic pump which draws hydraulic fluid from a reservoir
and pressurizes it to 21 MPa (3000 psi). The pressurized fluid is made available
to the hydraulic components in your test system.
Pressure The HPU can produce low and high pressure outputs:
• The low pressure output is approximately 1.4 MPa (200 psi). Low pressure
is normally used while installing a specimen.
• The high pressure can be adjusted to 21 MPa (3000 psi) or less. High
pressure is used for an actual test. When operating in high pressure, the low-
pressure vent is blocked.
Filtering
The filtration system protects against silting by cleaning the hydraulic fluid to an
ISO particle count of 16/13/9 or better. The filter change gage indicates when the
filter needs to be replaced.
A suction strainer protects the pump from larger particles when the fluid is
pumped from the reservoir. It is located in the bottom of the hydraulic fluid
reservoir.
Heat exchanger Hydraulic fluid temperature is maintained with a heat exchanger that cools the
fluid. The heat exchanger helps keep the temperature of the hydraulic fluid
between 64–68°C (147–155°F). The temperature of the fluid is monitored by an
overtemperature switch. If the fluid temperature exceeds 75ºC (170ºF), a switch
opens and shuts down the HPU. The system cannot be restarted until the fluid
cools. There are two kinds of heat exchangers:
• The water-cooled heat exchanger cools the hydraulic fluid as it passes over
water-filled tubes. A regulating valve can adjust the flow of water through
the tubes, and this affects the amount of cooling the heat exchanger can
accomplish.
• The air-cooled heat exchanger cools the hydraulic fluid as it passes through
a radiator. A fan blows air through the radiator to transfer heat from the
radiator to the air. Louvers control the airflow over the hydraulic radiator,
and this affects the amount of cooling the heat exchanger can accomplish.
Note For additional information, see the Heat Exchanger Care and Water
Quality Guide (MTS part number 015-164-000).