How it Works
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The pressure in the system quickly rises to 40 (or better) Psig. At this time,
the minimum pressure valve opens delivering Compressed air to the service line.
All the controls are inactive. The inlet valve is fully open, with the machine
operating at full capacity. The Compressor will continue to operate in this
manner between 40 and 100 Psig. If the Compressor is equipped with a turn valve,
spiral valve or capacity valve, those ports will be closed. Port 3 of the pilot
valve will be closed. Port 1 is open to port 2.
If the full rated capacity of air is not being used, line pressure will climb
above 100 Psig. At 100 Psig spring tension is overcome in the back pressure
regulator, allowing air pressure to travel to the inlet control valve actuator. The chamber in
the inlet control actuator inflates and the inlet valve starts to close. Between
100 and 105 Psig the inlet valve is controlled in this manner, matching air
intake with the amount of air being used.
When compressed air is not being used, the line pressure will rise to 110 Psig.
At this time, spring tension in the pressure switch is overcome, breaking
electrical contacts in the pressure switch. This de-energizes the pilot valve
allowing air pressure to enter through port 3 and out port 1. This signal
travels to the inlet control actuator which closes the inlet valve. The pressure signal
also travels to the blow down valve, operating the valve allowing excessive
pressure to be vented from the receiver (sump) tank. Port 3 is open to
port 1 and port 2 is open to atmosphere. .
Machines with dual controls require additional settings. Each individual
Compressor may require a study of the compressed air system before controls can
Re-load after modulation
The Compressor will continue to unload until line pressure drops under the
differential setting in the pressure switch. At that time, the pressure switch
contacts again close. With the pressure switch contacts closed the pilot valve
is again energized. This allows the pressure signal (which was holding the
blow-down valve open) to escape out port 2 of the pilot valve to atmosphere. The
pressure signal which was keeping the inlet valve closed vents out the bleed
orifice in the pressure regulator. With the inlet valve again open and the
blow-down valve closed, the Compressor will load back up, producing the full
rated capacity of the Compressor. Port 3 is closed and port 1 is open to port 2.
Note: It is important to keep the bleed orifice in the pressure regulator
unrestricted. If the orifice is plugged, the signal holding the inlet valve
closed cannot escape and the Compressor will not re-load
Capacity control system for machines equipped with spiral valve.
Spiral valve control adjustment
Explanation and instruction for setting the control system on a Sullair
Compressor with a spiral valve.
Control system functional description
The purpose of the Compressor control system is to regulate the amount of air
being compressed to match the amount of air being used. The system consist of a
inlet butterfly valve, spiral valve, two back pressure regulators, pressure
switch, pilot valves, control line shuttle valves and a blow down valve. For
explanation purposes, these instruction will apply to a air system that requires
100 Psig for plant operations.
Start mode - 0 to 50 Psig
When the on button is pressed, the sump pressure will quickly rise to 50
(±)Psig, the minimum pressure valve will begin to open and permit air to the
plant system. During this period, the back pressure regulators and solenoid
valves are closed and the Sullicon control is inoperative. The butterfly valve
is held in the open position while the spiral valve is held in the closed or
maximum position with spring tension. This allows the Compressor to operate at
its full capacity.
Full load mode - 50 to 100 Psig
At 50± Psig the air is permitted to enter the plant system and the plant air
pressure is continually monitored by the pressure switch. The pressure
regulators and solenoid valves remain closed, permitting the butterfly valve to
remains fully open and the spiral valve to be held in its maximum position. This
will continue until the system air pressure reaches 100 Psig.
Modulation - 100 to 110 Psig
The control system will allow the Compressor to maintain 100 Psig until the
capacity of the Compressor is reached at which time the pressure will begin to
drop. It will continue to drop if the demand is greater than the capacity of the
If the demand is less than the capacity of the Compressor, the back pressure
regulator, which controls the spiral valve will begin to open, allowing air to
enter the spiral valve actuator and begin to open the ports at the front of the
Rotors. This stops the Rotors from compressing their full length, thus
maintaining 100 Psig and at the same time reducing the energy demand.
This control cycle will continue to maintain 100 to 105 Psig And vary from
100% to 50% of the rated capacity of the Compressor by rotating the spiral valve
from the full closed Position to the full open position.
When the pressure reaches 105 to 106 Psig the back pressure regulator that
controls the butterfly valve will start to Open, permitting air to the Sullicon
control. The Sullicon Control will begin to move the butterfly valve from the
full Open position to a partially closed position and regulate the pressure
above 106 to 110 Psig. This will reduce the capacity
of the Compressor from 50% to 40% of it’s rated capacity. This cycle will
continue as long as the system demand stays At this level (50% to 40%). During
this range, the spiral valve Remains in the full open or unloaded position.
Unload mode - 110 Psig
When a relatively small amount or no air is being used, the system air
pressure will rise to 110 Psig at which time the pressure switch will
de-energize the solenoid valves, allowing line pressure to be supplied to the
Sullicon control keeping the butterfly valve closed, and restricting line
pressure to the spiral valve actuator. Spring tension will rotate the spiral
valve to it’s maximum position, ready for the Compressor to load again.
Simultaneously, the signal will be sent to the blow down valve which will open
and vent the compressed air (in the sump tank) to atmosphere, thus lowering the
sump pressure to the unload set point (65 Psig for maximum fluid separation).
The check valve in the system line leaving the Compressor will prevent the plant
air from flowing back into the unit. The system will remain in this condition
until the line pressure drops to the set (load) point of the pressure switch,
then the pressure switch will re-energize the pilot valves and the Compressor
will start it’s normal cycle again.
If the spiral valve starts to turn before the desired pressure is reached,
turn the adjustment screw on the regulator clockwise.
If the Sullicon control begins to close before it reaches 5 to 8 lbs. above
the setting of the spiral valve, turn the adjustment screw clockwise. If the
pressures go over the desired pressure, turn the adjustment screw
The difference in the control settings on your Compressors and the settings
in this manual will be the modulating and cut-in pressure of the pressure
switch. If you have the MEC controlling your Compressors, the cut-in pressure
for your Compressor must be 5 Psig below the cut-out pressure of 110 Psig.
(Obtain the MEC Controller manual for proper adjustment and settings).
The following pictures show the control circuit on the tandem Compressor with
spiral valve control. The red lines show sump or line pressure and the green
lines show atmosphere pressure. Follow the lines to see how the controls system
feeds air to the respected valve or cylinder. There are two regulators, one
pilot valve, normally open, one solenoid valve for the spiral valve that is
normally closed and another solenoid valve for the MEC that is normally open.
A. Inlet butterfly is open.
B. Spiral valve moves to full load position.
C. Both valves remain fully open as long as machine is running
at 100 Psig or below (full load mode).
2. Part load
100 to 50% range.
As air demand starts dropping, line pressure starts rising
above 100 Psig.
A. Differential pressure regulator opens allowing air flow
to spiral valve actuator.
B. The spiral valve start to rotate allowing intake ports to
open to the inlet chamber.
C. The spiral valve continues to open until all ports are
open. It will open and close ports to the Systems
demand or down to 50% of Compressors capacity.
3. 50% to 40% range.
A. Spiral valve will remain in the full open position.
B. The inlet valve regulator will begin to open allowing
air flow to the inlet control which will Start
to close the inlet valve. .
The inlet valve will throttle
from 50% to 40%. If air demand drops below the
40% level, the pressure switch contact will open de-energizing
the pilot valve. Air flow will then open the
blow down valve causing the machine to go into
an unloaded mode. The spiral valve will go into the
full load position
4. Back to full load.
A. When the pressure drops below the cut in pressure of the
pressure switch, the contacts in the pressure will
close. This will cause the pilot valve to close and
return the machine to the full load state.
Sullair® is a register name of Sullair Corporation.
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