Emerson Vilter VSS - Emergency Shutdown; Capacity and Volume Ration Control through Slide Valve Actuators; Figure 4-1. Slide Valve Motor Location

4 – 2
Section 4 • Operation
VSS/VSR/VSM/VSH/VSSH Compressor • Installation, Operation and Service Manual • Emerson • 35391S
the compressor slide valves must return below their
respective 5% limits before the compressor unit can be
restarted.
NOTE
Wait a minimum of 20 minutes (to allow the
compressor unit to equalize to suction pressure)
between pre-lubing or pushing the start button.
Emergency Shutdown
Emergency shutdown is initiated by the following:
1. A shutdown or trip condition of a process variable
while the system is in operation. If a process vari-
able reaches a high-high or low-low shutdown set-
point, the compressor unit will automatically stop.
A shutdown alarm is also generated on the control
panel HMI screen annunciating the specic process
variable trip condition.
2. The Local Emergency Shutdown push button locat-
ed on the side of the control panel enclosure. When
the Local Emergency Shutdown push button is acti-
vated, the entire unit powers down. Also, the com-
pressor capacity and volume slide valve will stay in
their last position until the unit is powered up. Once
recovery has been accomplished and the unit is to
be re-powered, the Local Emergency Shutdown
push button must be pulled out to power up the
unit and controls.
Capacity and Volume Ratio Control through
Slide Valve Actuators
Capacity and volume ratio control of the screw
compressor is achieved by movement of the respective
slide valves, actuated by electric motors.
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 4-1) to de-
crease the capacity 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 motors 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
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.
The Motor Amps Load Limit protects the compressor
from overloading by decreasing the compressor capac-
ity if the motor amperage is at the Maximum Amps set-
point, or preventing an increase in capacity if the motor
amperage is above the Full Load Amps setpoint. ( See
manual for the appropriate microprocessor.)
NOTE
Optical Actuators CAN NOT be manually rotated.
(The VSM 501-701 models will have motor locations
opposite of gure #4-1)
Figure 4-1. Slide Valve Motor Location