Section 11
VARIABLE SPEED DRIVE APPLICATIONS
60
pressure regulator controls the inlet control valve.
The orifice also bleeds any accumulated moisture
from the pressure regulator.
MODULATING MODE WITH OPTIONAL SPIRAL
VALVE- IN EXCESS 101.5 PSIG (7.0 BAR) TO 106
PSIG (7.3 BAR)
During low periods and with the Variable Speed
Drive at minimum speed, the line pressure can rise
above 101.5 psig (7.0 bar). In this case the I/P con-
troller releases air pressure to the spiral valve actu-
ator. Air pressure at the actuator expands the
diaphragm. The rack, in turn, engages with the pin-
ion mounted on the spiral valve shaft assembly.
This results in a rotary motion. As the spiral valve
rotates, it starts opening the bypass ports gradually.
Excess air is then being returned back internally to
the suction end of the compressor unit. Now the
compressor is fully compressing only that amount
of air which is being used. As air demand keeps
dropping further, the spiral valve keeps opening
more and more until all bypass ports are fully open.
At this point, if the discharge pressure continues to
rise, the compressor will unload at 106 psig (7.3
bar).
UNLOAD MODE- IN EXCESS OF 106 PSIG (7.3
BAR)
When a relatively small amount or no air is being
used, the service line pressure continues to rise.
When it exceeds 106 psig (7.3 bar), the Supervisor
control system de-energizes the solenoid valve
allowing sump air pressure to be supplied directly to
close the inlet valve. Simultaneously, the solenoid
valve sends a pneumatic signal to the blow down
valve. The blowdown valve opens to the atmos-
phere, reducing the sump pressure to approximate-
ly 18 psig (1.2 bar). The check valve in the air serv-
ice line prevents line pressure from returning to the
sump. The compressor will shut down after the
unload time setting expires if programmed.
When the line pressure drops to the low setting
pressure of 100 psig (6.9 bar) The Supervisor
Controller starts the motor and ramps it up to the
minimum speed set by the VSD and energizes the
solenoid valve which closes the blow down valve.
The re-energized solenoid valve prevents line pres-
sure from reaching the inlet control valve, thereby
allowing the valve to fully open.
AUTOMATIC OPERATION
For VSD applications, the Supervisor Controller
should be set in the “Automatic” mode. This mode
allows the compressor to shutdown when no com-
pressed air requirement is present and restarts
when compressed air is needed.
Table 11-1 Package Selection Chart- Factory Settings
Series Model Pressure Factory Settings Maximum
Supervisor Settings Frequency VSD Settings Motor
Full Load Unload Command Maximum Frequency Minimum Frequency Speed
HP PSIG PSIG (I) PSIG PSIG Hz (II) Value (III) Hz (II) Value (III)
LS20V 100 100 100 106 101.5 83.0 691 25 209 2450
125 125 131 126.5 77.1 637 25 209 2288
150 150 156 151.5 67.3 561 25 209 1997
W/SPVL 100 100 106 101.5 63.3 527 25 209 1878
W/SPVL 125 125 131 126.5 62.3 519 25 209 1847
(I) Set regulator valve 1.5 psig above full load pressure (applies to non-spiral valve compressors only).
(II) Max/Min Hz used for lap top entry.
(III) MAX/MIN Frequency value is used for key pad entry.
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