Operation
Series 505G2 SilentFlo™ Hydraulic Power Unit 55
l Keeping the HPU in low pressure effectively isolates the external or system flow because the
relative back pressure is normally much higher in the external system circuit.
l Running the HPU in low pressure maximizes fluid flow, allowing the HPU to circulate the
reservoir contents across the filter more times per hour.
l Starting the commissioning process with an isolated HPU reduces the possible number of
problems encountered during startup.
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:
l Because the motor is not working to pressurize the fluid, it runs at a low power level, producing
less waste heat.
l 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:
l Leaving an HPU idling in high pressure mode uses roughly 40% more electrical power than
idling in low pressure mode.
l 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 over-temperature 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.
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