With its dumpy fat cylindrical shape, dull-painted exterior, lack of visible dynamic activity, and frequently hidden location, it’s easy to understand why the air receiver usually is the orphan of the plant-air system family. There is confusion and controversy over its function, where it should be located, what size it should be, how it should be piped — and whether it is needed at all. Air receivers are one of the least understood, yet potentially most useful components available to increase operating efficiency. But an air receiver should be an integral part of any plant air system — mainly to enhance its efficiency. Here are the classic purposes:

Contaminant removal — A bare receiver (without a pressure regulator or flow controller) adds a large volume to the piping system. This volume reduces air-flow velocity and encourages finely divided particles of liquid lubricant or condensate to drop out of the air stream. These separated liquids can then be drained from the receiver, rather than traveling with the compressed air or gas to create adverse downstream effects.

Pulsation damping— A receiver installed near the compressor discharge dampens pressure pulses from positive-displacement compressors (rotary or reciprocating) to a small fraction of their original amplitude. This reduces the probability of excess compressor power or shortened service life resulting from resonant response to the frequency of compressor delivery.

Pressure stabilization— A receiver combined with a pressure regulator or flow controller can create an effective pressure band or differential between the supply side and the demand side. A typical example: 95 psig in the receiver, 90 psig steady to the system. This allows the demand side to operate at its lowest effective pressure, and therefore lowest volume demand. Stored air with a pressure differential creates volume held in reserve to cover short-term peak demands that exceed current air supply — without turning on or loading another compressor.

A one-atmosphere pressure change (less than 15 psi) accommodates a free air volume equal to that of the receiver. This can be used in the primary receiver, in a secondary receiver on the demand side (to serve an operation with surge demand), or even as off-line peak-shaving storage.

Augment compressor controls— Receivers with appropriate volume can reduce and decelerate pressure changes caused by intermittent use of compressed air. Compressor controls, which normally respond to pressure, can smoothly regulate compressor output without frequent ranging through their full control span. If an operation has capacity controls, but only a short run of pipe, a receiver will provide the total storage volume needed for the control to perform effectively.

Other effective ways to manage a stable pressure exist, depending on system dynamics. A networking control system can manage the compressed-air supply to hold a set target pressure at the system entry. Also, a variable-speed drive trim compressor can hold a pressure differential as low as 1 psig throughout its full operating range, eliminating the control band rise.

Pressure stabilization— A receiver combined with a pressure regulator or flow controller can create an effective pressure band or differential between the supply side and the demand side. A typical example: 95 psig in the receiver, 90 psig steady to the system. This allows the demand side to operate at its lowest effective pressure, and therefore lowest volume demand. Stored air with a pressure differential creates volume held in reserve to cover short-term peak demands that exceed current air supply — without turning on or loading another compressor.

A one-atmosphere pressure change (less than 15 psi) accommodates a free air volume equal to that of the receiver. This can be used in the primary receiver, in a secondary receiver on the demand side (to serve an operation with surge demand), or even as off-line peak-shaving storage.

Augment compressor controls— Receivers with appropriate volume can reduce and decelerate pressure changes caused by intermittent use of compressed air. Compressor controls, which normally respond to pressure, can smoothly regulate compressor output without frequent ranging through their full control span. If an operation has capacity controls, but only a short run of pipe, a receiver will provide the total storage volume needed for the control to perform effectively.

Other effective ways to manage a stable pressure exist, depending on system dynamics. A networking control system can manage the compressed-air supply to hold a set target pressure at the system entry. Also, a variable-speed drive trim compressor can hold a pressure differential as low as 1 psig throughout its full operating range, eliminating the control band rise.

Controlling energy costs

When industry management began to focus on energy-cost control to reduce production costs, energy managers soon realized that compressed air was their most expensive utility. After all, it takes 8 hp of electricity to produce 1 hp of compressed air. Air no longer was perceived as free. Its cost should,
and could, be managed.

Early efforts in compressed-air cost management focused on the obvious — controlling leaks and lowering usage. But after a significant reduction in air usage, an energy audit often revealed little or no reduction in actual electric power consumed. This disappointing result usually came because of the absence of an air receiver, combined with poor or too small interconnecting piping from the compressor to the system entry.

Insufficient effective storage did not allow the compressor capacity controls to translate lower air demand into lower input energy. Without effective storage, most unloading controls could not establish and hold enough idle time as a percent of running time. Nor could they optimize the automatic start/stop control and shut off.

The normal operating band for a compressed air supply is 10 psig. Effective storage capacity is created at the location where this band is neutralized In other words, a 10-psig operating-pressure band is neutralized at the point where 10 psid is needed to get air through the interconnecting piping, dryer, filters, etc. and into the demand system.

Hank van Ormer is President, Air Power USA Inc., Pickerington, Ohio. For more information, call (740) 862-4112 or visit www.airpowerusainc.com.