Dunham-Bush ACDX, Installation, Operation And Maintenance Instructions

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COMPRESSOR MODEL
SSCB050
SSCB060
SSCB075
CRANKCASE OIL
SERVICE VALVE
SIGHT GLASS
CRANKCASE HEATER
HIGH PRESSURE PORT
UL-1
UL-2
UL-3
COMPRESSOR MODEL
SSCA050
SSCA060
SSCA075
CRANKCASE OIL
SERVICE VALVE
SIGHT GLASS
CRANKCASE HEATER
HIGH PRESSURE PORT
UL-1
UL-3
UL-2
The DB screw compressor capacity control system for infinite
modulation consists of a slide valve and hydraulic piston/cylinder
operator internal to the compressor, plus three hydraulic solenoid
valves (UL-1, UL-2, & UL-3) piped externally.
The slide valve forms a portion of the chamber wall in which the
rotors turn; thus, its position with respect to the rotors determines
the effective rotor length and thereby the percent of full load
capacity.
Upon compressor start-up, UL-3 is opened (energized). This
allows oil pressure to act upon the hydraulic piston, holding it in
the fully unloaded position. After 30 seconds, during which time
full oil flow is established to all bearing surfaces, UL-3 is closed
(de-energized). At this point, temperature controller is free to
open or close UL-1 and UL-2 in response to the supply water
temperature.
The slide valve will move to the left (loading) by force of discharge
pressure, whenever UL-1 opens to permit flow to the oil return
(low pressure) line. The slide valve will move to the right
(unloading) whenever UL-2 opens the oil supply (high pressure)
line, since the force of the oil exceeds that of the discharge gas.
The temperature controller sends a series of electrical “pulses”
to the appropriate solenoid to adjust to load conditions. The
further the supply water temperature is from the controller set
point, the longer is the duration of the pulses. The series of pulses
will continue until the controller is satisfied. As the water
temperature approaches the set point, the pulses become quite
brief to prevent overshooting the set point.
This method of compressor unloading, in conjunction with supply
water sensing, minimizes action/reaction lag time and overshoot
resulting in an exceptionally precise and stable control of supply
water temperature.
SLIDE VALVE
UNLOADING SYSTEM
8
The following table lists solenoid valve position for all three
operating modes.
UL-1 UL-2 UL-3
Starting Close Close Open
Loading Open Close Close
Unloading Close Open Close