Using the AS-2 vs. the AS2PT

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The AS-2 Controller

Using the AS-2 Controller on Recip and Rotary Compressors with Standard Mechanical Pressure Switches and the AS2PT Controller for Compressors with Dual Control and the 6 Min Time-Out-To-Stop Control


The AS-2 Universal AutoSync has been used on Atlas Copco, GD, Champion, Curtis, I-R, Powerex and other basic rotary and recip compressors for over 15 years with hundreds of successful installations.

The parameters for a successful AS-2 application are:

1.  The control voltage -- i.e., the signal from the mechanical pressure switch to the starter  coil -- can be 24v, 115v, 200 or 230 volts. It cannot be 460 volts or above;

2.  The operating mode must be start/stop control;

3.  The AS-2 Automatic Lead/Lag Controller can be used to automatically lead/lag control a variety of machines beyond the compressor world.  We have installations on heat exchangers, centrifugal pumps and refrigeration compressors, to name a few.

Here is the problem:
The AS-2 controller works perfectly when the compressors have standard pressure switches and start/stop control. During the lead/lag control set up and cycle Comp 1 is always set at a higher pressure then Comp 2.  So that in this position Comp 1 will always lead and Comp 2 will always lag.

When the system alternates to Comp 2 lead and Comp 1 lag, then Comp 2 is reading Comp1's pressure switch (the high setting) and Comp 1 is now reading Comp 2's pressure switch (the low setting).  That is how we achieve lead/lag control without resetting the pressure switches for each alternating cycle.

The AS-2 cannot be used on air compressors that have automatic dual control.  That is, a compressor which when the signal to stop is received from the pressure switch the compressor goes into the idle or unload mode and stays there for 6 minutes--unless a call for air is sensed, in which case the machine will begin its normal pumping cycle --before it is stopped.

When the compressors have the 6 min time out feature we cannot use the AS-2 controller. Here is why:  With the 6 min time out feature the compressor continues to run and unloads all of the compressed air produced by the compressor by blowing off the load through a Solenoid Valve mounted on the compressor separator tank.  It does this for 6 minutes (unless it gets a pump signal again).

The problem for us occurs when the compressors with this 6 minute control alternates.  Comp 2 is now the lead compressor and Comp 1 is the Lag compressor reading the other compressor's pressure switch. That part works as normal EXCEPT COMP2 WHICH IS READING COMP 1'S PRESSURE SWITCH WILL NOT GET ITS OWN UNLOADER SOLENOID VALVE TO OPEN--AND THE SOLENOID VALVE ON COMP 1 OPENS SINCE THAT IS THE PRESSURE SWITCH GIVING COMP 2 ITS SIGNAL. THIS WILL RESULT IN OVER PRESSURIZING THE SYSTEM AND BLOWING THE SAFETY VALVE.

As you can see that will not work!

The AS2PT Controller


In the case of the air compressor with the 6 min stop feature we have the AS2PT controller which has been specifically designed to work two rotary compressors with mechanical pressure switches AND the automatic dual control option -- or 6 min unload period.


The AS2PT controller fixes that problem by supplying the pressure signal to the starters and proper unloader solenoids simultaneously, completely overcoming the 6 min time out problem by using Pressure Transducers to control the two compressors. The SMC pressure transducers include a pressure display and easy to field-set pressure changes.

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WHEN THE COMPRESSOR HEAD HAS NO BUILT-IN AUTO INITIAL UNLOAD MECHANISM

 When the duplex compressor system uses the FORM X (unloader type) pressure switches for automatic initial unloading on start-up, meaning that the independent compressor is not equipped to unload itself on start-up and must have an external method of loadless start, you must use the AS-2 or AS2PT PLUS the optional "5-second totally unloaded soft start" feature.

  

Example Installation:  For the two Atlas Copco AR series 4 cylinder, 2 stage recips sold by NAPA, the customer required automatic lead/lag control.  Since the Atlas Copco AR series does not have a compressor mounted automatic start-up unloading device, they used the FORM X type pressure switch which exhausts the compressed air in the discharge line when the compressor stops.  However, the pressure switch unloading device must be eliminated when using the AS-2 Universal AutoSync controller and our 5 second automatic loadless start system substituted for unloaded starts.  The picture to the right illustrates how the single solenoid valve is piped into the interstage coolers to unload both cylinder banks.  The AS-2 controller is wired to the 1/4" solenoid valve and supplies the logic to open the valve for 5 seconds on each start-up for loadless start.

AS-2 Wired to Solenoid Valve Piped into the Interstage Coolers to Unload Both Cylinder Heads

AS-2 Wired to Solenoid Valve Piped into the Interstage Coolers to Unload Both Cylinder Heads