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7.2 LOAD / RELIEF
In this operating mode, the unit will operate on load or in relief between the start and stop times. When operating in relief for a period longer than
relief time the main motor will stop and the product will enter into standby mode. When the pressure reaches a lower value than load pressure,
the main motor will start automatically.
7.3 CONTINUOUS OPERATION
The equipment will maintain the main motor running continuously from start time until a stop request is triggered, regardless of whether the
compressor is under load or in relief.
7.4 PRESSURE DROP
Two set periods; "on-load period" and "relief period" are used to select the product's operating mode when the discharge pressure is higher than
the relief pressure. These two periods are adjusted according to the maximum number of starts per hour allowed for the main motor. The on-load
period starts every time the compressor is switched on. The on-load period will be as long as the time the motor is running and ends when the
compressor enters into standby mode. The relief period starts each time the compressor goes into relief. It lasts the entire relief time and also
while the compressor is in the standby mode. It ends the moment the compressor goes into on-load. Each transition is separated by the product's
cooling time.
The following transition cycles are allowed:
• The discharge pressure drops to a value below the load pressure, the compressor goes into on-load regardless of its previous operating
mode. If the main motor is stopped it will only start after cooling time.
• If the discharge pressure reaches a value higher than the relief pressure in a time longer than the "relief period", the compressor will enter
into standby mode after the relief time set on the interface has elapsed.
• If the discharge pressure reaches a value higher than the relief pressure in a time shorter than the "relief period" the relief time is calculated
by taking into account the pressure drop time of an earlier load cycle as follows:
• If the pressure drop time (time the discharge pressure takes from relief pressure to load pressure) is greater than the "relief period", the
compressor enters into standby mode immediately after the relief time set on the interface.
• If the pressure drop time is shorter than the "relief period", the compressor goes into relief, with the motor still running, however, in this
case the relief time will not be the value set on the interface, but rather the "relief period"..
7.5 DYNAMIC RELIEF CONTROL
The relief time is dynamically increased or decreased by the dynamic relief control in relation to the maximum number of starts by hour allowed
for the main motor. The motor's number of starts by hour is measured by the Control Net interface. A very large number of motor starts causes the
relief time to increase in the same way that a small number of starts causes the relief time to decrease.
7.6 VARIABLE SPEED CONTROL
Variable speed control creates a PID control sent to a frequency inverter using the analog output (4-20mA) in order to vary the speed of motor's
rotation and maintain the discharge pressure of the compressor as the set value (load pressure).
Variable speed control is used to maintain the compressor discharge pressure at the load pressure value. If the pressure rises to the relief pressure,
the load solenoid valve is de-energized and the compressor goes into relief. While the compressor remains in relief the motor rotation will remain
at a preset value, usually equal to the minimum operating rotation. If the equipment remains in relief for a period longer than relief time, the main
motor will stop and the compressor will enter into standby mode. When the pressure falls below the load pressure, the motor will start, if it is in
standby mode, the load solenoid valve will be energized and the motor will operate throughout its speed range.
If connected to the Schulz Control compressor manager and the compressor room has more than one variable speed compressor, any FLEX com-
pressor selected as a "base compressor" will operate at the optimum speed set on its interface. The FLEX compressor set as the main compressor
will use its entire speed range to perform pressure control. In addition, the working pressure of the variable speed products will be automatically
modified to the pressure set on the Control manager. Therefore, up to 12 variable speed compressors can operate in a coordinated manner in the
same air network, using exactly the same pressure control.
7.7 ENABLE FORCED RELIEF
When activated, hold the "START" button pressed and use the "DOWN" button to force the compressor to switch from on-load status to in-relief
status. The product will not go into on-load until the forced relief condition is removed. To remove the forced relief condition: simultaneously press the
"START" and "DOWN" buttons and the compressor will return to normal operating conditions.
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