Emerson VSG & VSSG Spezifikationen PDF herunterladen (Seite 27)

100

Operation

CONTROL SYSTEM

A. Screw Compressor Control And Operation

1. Starting, Stopping and Restarting the Compressor.

Before the screw compressor unit may start, certain

conditions must be met. All of the safety setpoints

must be in a normal condition, and the suction pres-

sure must be above the low suction pressure setpoint

to assure that a load is present. When the “On-Off”

switch or “Manual-Auto” button is pressed, the oil

pump will start. When sufficient oil pressure is built

up and the compressor capacity control and volume

ratio slide valves are at or below 10%, the compressor

unit will start.

If the compressor is in the automatic mode, it will

now load and unload and vary the volume ratio in

response to the system demands.

Stopping the compressor unit can be accomplished

a number of ways. Any of the safety setpoints will

stop the compressor unit if an abnormal operating

condition exists. The compressor unit “On-Off” or

stop button will turn the compressor unit off as will

the low pressure setpoint. If any of these conditions

turns the compressor unit off, the slide valve motors

will immediately energize to drive the slide valves

back to 5% limit. The control motors will be de-

energized when the respective slide valve moves back

below 5%. If there is a power failure, the compressor

unit will stop. If the manual start on power failure

option is selected (see appropriate Microprocessor

Instruction Manual), restarting from this condition is

accomplished by pushing the reset button to insure

positive operator control. If the auto start on power

failure option is selected (see appropriate Micropro-

cessor Instruction Manual), the compressor unit will

start up after a waiting period. With both options,

the compressor slide valves must return below their

respective 5% limits before the compressor unit can

be restarted.

2. Slide Valve Control Actuators

Capacity and volume ratio control of the screw com-

pressor is achieved by movement of the respective

slide valves, actuated by electric motors.

SLIDE VALVE ACTUATOR LOCATION:

VSG 401 CCW

When viewing the compressor from the discharge

end (opposite the drive end), the upper motor is

for capacity control. The command shaft turns (see

Table 1) to decrease the capacity to 10% and reverses

to increase the capacity to 100%. The lower motor is

for volume ratio control. The command shaft turns

(see Table 1) to reduce the volume ratio to 2.0, and

reverses to increase the volume ratio to 5.0.

Actuation of the electric motors can be done manu-

ally or automatically. To actuate the motors manu-

ally, place the desired mode selector in the manual

position and push the manual Increase or Decrease

buttons. In the automatic mode, the microproces-

sor determines the direction to actuate the electric

motors. However, in the automatic mode, there is an

“On” and “Off” time for the capacity control motor.

The “On” time is the time in which the slide valve

moves, and the “Off” time is the time in which the

system is allowed to stabilize before another change

in slide valve position.

Note:

Optical Actuators CAN NOT

be manually rotated.

SLIDE VALVE ACTUATOR LOCATION:

VSG 501 CW Thru VSG 701 CW

View Capacity

View Volume

Ratio

View Volume

Ratio

View Capacity

1 2 ... 22 23 24 25 26 27 28 29 30 31 32 ... 99 100

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