Do I need an air tank? In most circumstances, yes, you do.
Compressed air receivers are storage tanks that provide several benefits for your compressed air system.
- Air receivers serve to smooth out pulsations and vibration in the air line from the compressor, especially reciprocating compressors.
- Air receivers provide storage capacity to evenly match output to air demand from plant operations. This prevents the compressor from running for an excessive amount of time and prevents frequent cycling of the compressor.
- The storage capacity provided by receivers allows time for the controls to react to the demands of the system for air.
- The air receiver will also serve as a collecting point for condensed moisture from the air line. This of course must be drained from the receiver.
Sizing of air receivers is not an exact science. There are several rules of thumb for sizing the tanks, and vary depending on control type and compressor size. Also, the air piping in the plant can serve as receiver capacity if it is large enough diameter. One rule of thumb calls for 1 gallon of receiver capacity for every CFM of compressor capacity. Another calls for 3 gallons of receiver capacity for every CFM of compressor capacity. Compressed Air and Gas Institute (CAGI) publishes charts based on compressor capacity and control method to select a receiver.
Receivers can be either “wet receiver” or “dry receiver”. This refers to the location of the receiver relative to the air dryer. The receiver placed before the air dryer in the line will be a wet receiver. It will accumulate the condensed moisture and must be diligently drained to prevent passage of water downstream. The receiver placed after the air dryer will generally be a dry receiver. If the dryer is refrigerated type or deliquescent type, it may still accumulate water and must be drained. If the dryer is a twin-tower regenerative type, there is little likelihood of moisture accumulating in the tank.
Receivers are pressure rated and considered by ASME as a pressure vessel. They must be provided with an adequately sized and rated pressure relief valve. This protects the air receiver and keeps it from over pressurizing. This also provides a measure of protection for the compressor as well as downstream piping and equipment.
In addition, a pressure gauge is recommended and usually supplied with the air receiver. As mentioned above, the accumulated moisture must be drained from the tank. The drain valve can be as simple as a manual ball valve which must be manually opened to drain. Other drain valve options are electric timed automatic drain valves, mechanical float-type drain valve, and more sophisticated zero air loss drain valves. The latter are energy saving devices that only allow water to escape, and prevent the compressed air from being wasted.
Pye-Barker Supply Co. sales engineers are experts in sizing and applications of air receivers and other compressed air products. We represent several manufacturers such as Steel Fab, Silvan, and others. Most common sizes are available from manufacturer’s stock.