MTS Model 512-04 Hydraulic Power Unit - Manual (Page 6)

Model 512.04 Hydraulic Power Unit 6 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 8 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 13.8 MPa (2000 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 13.8 MPa (2000 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 14/11 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.