MTS Series 505G2 SilentFlo Hydraulic Power Unit Model 505G2-11 - Manual (Page 51)

Low/High Pressure Functionality
Model 505G2.07/.11 SilentFlo™ HPU 51
A logical progression of fluid conditioning that begins at the HPU is required to
minimize problems when commissioning a system.
• With the HPU running in low pressure, acceptable particle counts are
obtained in a relatively short time.
• 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.
• Running the HPU in low pressure maximizes fluid flow, allowing the HPU
to circulate the reservoir contents across the filter more times per hour.
• 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:
• 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 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.