9.13.1 MBV Control
The valve actuator operates on 24 VAC power and is controlled by a 2 to 10 VDC proportional control
signal. The valve full-open to full-close time is 60 seconds. At 2 VDC the valve is closed; at 10 VDC the
valve is fully open. There is a 20-second delay to position the motorized ball valve before starting the
compressor.
9.13.2 MBV Control Method
The control utilizes an upper and lower pressure threshold with a 35 psi (241 kPa) deadband to reduce
valve movement. If the liquid pressure is between the upper and lower threshold the valve remains at the
current position. If the liquid pressure exceeds the upper threshold the valve opens, and if the pressure
falls below the lower threshold the valve closes. There are multiple adjustment bands to ease discharge
pressure back into control range.
9.13.3 MBV Adjustment
Both pressure thresholds can be shifted simultaneously over a 50 psi (35 kPa) range (the 35 psi [241 kPa]
differential remains constant). The ball valve setpoint offset parameter in the Service menu can be
adjusted from 0 to 50 psi (345 kPa) to raise or lower the control band similar to the pressure adjustment
on a water regulating valve. Changing the setpoint offset will adjust the pressure thresholds for both
circuits. Units are factory set at a 30 psi (207 kPa) setpoint offset (30 psi [207 kPa] above minimum). This
results in a 220psiA (1517 kPa) lower threshold and a 255 psiA (1758 kPa) upper threshold pressure.
9.13.4 MBV Start-up
The setpoint offset is adjusted to the minimum value during start up, then transitions to the set value
once the compressor reaches normal operating pressures. Due to the control dead band it is possible for
each circuit to stabilize at different pressures within the dead band. Additionally changes in fluid
temperature could cause pressure changes that do not result in valve movement within the dead band.
Fan cycling stats should be set to prevent continuous fluid temperature swings greater than 10
o
F (5.6
o
C)
(see Drycooler Aquastat Settings on the facing page).
9.13.5 MBV Location
The motorized ball valves are located in the condenser fluid return line. Three-way valves are piped in a
mixing arrangement with the common port at the valve outlet.
9.13.6 MBV Manual Control
The valve can be manually set by disconnecting AC power, depressing the manual override button on the
valve actuator, and adjusting the valve position with the handle. Motorized ball valves may be controlled
through the Service menu using manual mode to override the normal control.
Vertiv | Liebert® PDX™ and PCW™ Installer/User Guide | 88
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