Emerson VSM, VSR, VSS service manual Operation, Slide Valve Motor Location

Operation

“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 accom- plished a number of ways. Any of the safety setpoints will stop the compressor unit if an abnormal operating condition exists. The com- pressor 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 ap- propriate 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 fail- ure option is selected (see appropriate Micro- processor 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 compressor is achieved by movement of the respective slide valves, actuated by electric motors.

Note:

Optical Actuators CAN NOT be manually rotated.

(The VSM 501-701 models will have motor locations

opposite of figure #6)

FIGURE 5.

SLIDE VALVE MOTOR LOCATION

When viewing the compressor from the dis- charge end (opposite the drive end), the upper motor is for capacity control. The command shaft turns (see Table 1) to decrease the capac- ity to 10% and reverses to increase the capacity to 100%. The lower motor is for volume ratio control. The command shaft turns 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 manually or automatically. To actuate the mo- tors manually, place the desired mode selector in the manual position and push the manual Increase or Decrease buttons. In the automatic mode, the microprocessor determines the direc- tion 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.

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