Aerzen USA insights and guidance for blower, compressor and vacuum pump applications

Lowering start-up power draw with across the line start - PD blower

Posted by Ralf Weiser on Mon, May 02, 2011 @ 04:36 PM

The most common motor start is what is commonly known as “across the line” (direct) motor start.  Power companies like when consumers do this as the resulting power draw (Amperage) spike is typically assessed with so called power demand charges on top of the regular power consumption charge in cents/kWh.  In any application where the blower or compressor must start against header pressure this starting method carries the greatest penalty as the motor must overcome the rotating equipment’s moment of inertia and the system pressure.  The graph below illustrates the power draw and the time it takes to bring the blower / compressor on line.  An Aerzen Aeromat automatic start-up unloading valve may be the answer to your problem. 

Positive Displacement Blower Starting Diagram

The line C shows the power draw needed with an unloaded machine.  Line A depicts the start up curve with full header pressure at time of start up.  Line B represents the power draw with an automatic start up unloading valve.  It is almost as good as the unloaded start up.  Major spikes upon start- up are avoided. 

Please find below the device that achieves this without any external auxiliary power.  The Aeromat valve is produced by Aerzen and its operation is as follows: 

 Aerzen Aeromat Valve

The unloading valve is a normally open device. Thus when the blower is started, the discharge air of the blower is diverted from the process piping (due to the closed check valve) through the unloading valve and out the vent opening (2). As the air flows through the valve a small amount of air travels up the spindle (5) to pressurize the top of the diaphragm (6). Ultimately the force resulting from the pressure on the diaphragm overcomes the spring force and the valve (7) closes, diverting the blower airflow back to the process piping. Normal closing time is 30-35 seconds, which is adjustable with the spindle (8).  The Aeromat does not need any sort of external electrical or pneumatic auxiliary power.  In some cases a solenoid valve (9) is installed allowing customers to take the blower or compressor off line while not having to shut it down completely. 

 Aerzen Aeromat Valve Image

Saving energy cost will become increasingly important.  Please check out the following video explaining the Aeromat’s functionality. 

Please drop me a note in case you have comments, suggestions or questions.    

Aerzen USA Ralf Weiser Technical Manager

Ralf Weiser
Technical Manager
Aerzen USA

Tags: positive displacement, Aerzen USA, pd blower, rotary lobe blower, blower sizing

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