MTS Series 505 SilentFlo Hydraulic Power Unit Model 505-30 User Manual

Page 52

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Model 505.20 - 505.30 SilentFlo™ HPU

52

Low/High Pressure Functionality

Operation

Once the HPU has cleaned the reservoir hydraulic fluid, sections of the system
should be isolated and sequentially cleaned. Flushing of hard line sections takes
place in high pressure mode. If the HPU is run in low pressure, flow losses in the
system will minimize the external flow and reduce the effectiveness of the
system flushing and fluid conditioning.

System Cooling

A Series 505 HPU running in low pressure maximizes the cooling efficiency of
the unit:

Because the motor is not working to pressurize the fluid, it runs at a low
power level, producing less waste heat.

Flow rates are high in low pressure mode, providing an ample volume of
coolant (hydraulic fluid) with a lower BTU per gallon heat content to the
heat exchanger. The heat exchanger operates with greater efficiency when
flows are near the designed flow rate as boundary layers are minimized.

Energy consumption

All Series 505 HPUs have variable volume pumps. Switching from high to low
pressure operation when external demands are absent will conserve energy and
water:

Leaving an HPU idling in high pressure mode uses roughly 40% more
electrical power than idling in low pressure mode.

When the hydraulic fluid is pressurized, cooling water usage is higher.
When operating in low pressure, the motor consumes less energy and less
heat needs to be removed by the heat exchanger.

Hydraulic fluid

replacement

New fluid right out of the barrel is the dirtiest the fluid will ever be in a properly
maintained system. Particle counts are well beyond safe limits for servohydraulic
components. Use the system commissioning methodology (filter new fluid first
when possible) to condition the fluid when introducing new fluid into a system.

Overtemperature

recovery

Cooling tower, chiller failures, or shut-off valves cause a large number of
overtemperature interlock conditions in the field. Low pressure mode is the
fastest way to get the tank temperature back to normal. Each HPU has an
override feature to force the unit into low pressure for fast over temperature
recovery.

High pressure

When the Series 505 HPUs are running in high pressure, a considerable amount
of heat is generated. During normal testing, this heat is dissipated by running the
hydraulic fluid through the system to the return line to the heat exchanger. During
periods of low system demand, this heat is dissipated by running the hydraulic
fluid through the auto-cooling circuit to the heat exchanger.

Auto-cooling

The auto-cooling valve is adjusted such that the shift between valve closed and
valve opened occurs just below the output pressure level. Whenever system
pressure is above the shift level of the auto-cooling valve (indicating low system
demand), the valve opens to port hydraulic fluid through the return filter to the
heat exchanger. When system pressure drops below the shift level (indicating an
increase in system demand), the valve closes and full flow is available to the
system.

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