Air Receivers Information
Air receivers serve as buffers between a compressor and the consumption mechanism of a compressed air system. They are essential the compressed air system operation and are present in most industrial buildings. They are also found in assembly lines to manufacture products or to operate tools. They are also known as air tanks.
Air receivers stabilize the pressure in system while acting as a storage medium where liquids are separated from an air stream. Receivers also moderate power pulses, so compressed air systems do not generate excessive power. In conjunction with compressor controls that regulate and adjust output pressure, air receivers ensure function and longevity of a compressed air system.
Compressed air systems face differing demands for capacity during operation. During periods of peak demand, the need for compressed air can exceed the compressor's output capacity, but air stored in the air receiver aids supplements supply. Most air compression systems consist of two air receivers:
- A primary receiver placed near the compressor and following the after-cooler, yet ahead of filtration and drying equipment.
- A secondary receiver or receivers placed near locations where larger intermittent air consumption occurs.
In a properly-designed compressed air system, the maximum capacity of the compressor is greater than the system's maximum mean air consumption. Because of this, the system must regulate the compressor's capacity during the operating process. Regulation occurs through on/off switching or more advanced processes using compressor controls to activate frequency drives and inverters. Basic methods such as on/off switching lead to greater pressure variation when compared to more advanced processes.
Air consumption demand varies depending on the process supported. In addition to increasing storage capacity, air receivers in a compressed air system serve a variety of functions including:
- Equalizing variation in pressure caused by the on/off and modulating cycles taking place in the compressor
- Collecting condensate and water taken from the air passing through the condenser
- Air storage for use in equalizing system pressure during periods of variable consumption and demand
- Reducing stress on the compressor, motor, and the system for controlling capacity by the avoidance of excessive compressor cycling
- Preventing pulses from occurring on the discharge line
- Separating moisture, oil, and other particles occurring in the air as it exits the compressor, or that may be brought over from the cooling equipment
- Limiting dew point and spikes in temperature
- Providing added storage capacity to accommodate air usage surges
Reducing energy costs by limiting demand for electric power caused by overly-frequent starting of the compressor motor
Compressed air systems come in two main types: oil-free and lubricated. Applications that require pure compressed air, such as medical or pharmaceutical applications, will use oil-free systems to avoid the risk of contamination by carbonized. Lubricated systems rely on a lubricant to minimize the friction caused by moving parts. Within these broad categories of compressed air systems are further categories such as high pressure, reciprocating, portable, and electric.
Air receivers also feature a variety of types, including wet and dry receivers that can be either vertical or horizontal.
Wet receivers add to a system's storage capacity and cut down on moisture. They use the substantial surface area of an air receiver as a free cooler to remove wetness. Reducing moisture at this point minimizes the load placed on filters and dryers. A wet receiver refers to the placement of the storage vessel or tank right after the compressor. Wet receivers are used for removing contaminants, stabilizing pressure, and pulsation reduction.
Dry receivers help air compression systems accommodate sudden substantial demands for air. They minimize drops in air pressure and are located after the air dryer and other equipment. Also called secondary air receiver tanks, dry receivers are placed intermittently near operating equipment to balance out the intermittent process. This procedure reduces the instantaneous requirement of the system as a whole.
Compressed air receivers classified as vertical are of two types: leg support and ring base. Pump mount receivers are of smaller size and are constructed with flat tops to enable motor and compressor mounting. This design allows them to withstand vibrations generated by the motor and pump. Remote receivers are larger units installed at a distance from the compressor.
A common formula for sizing an air receiver is:
Safety relief valves: Recommended for all receivers that contain compressed air. A standard setting for the valve is 10% above the highest system pressure requirement. However, it should not be set above the pressure rating specified for the connected tank.
Condensate drains: These drains remove liquid from the receiver tank. If a manual drain does not open on a scheduled basis, an automatic-timer drain is recommended.
Pressure gauge: If the gauge is rated at double the operating pressure of the system, it enables the needle to point straight up in normal position.
Gauge snubber: Used to protect the gauge if a pressure spike occurs.
A number of regions require air receiver tanks to follow a code requirement. Many use the code established by the American Society of Mechanical Engineers (ASME). The Occupational Safety and Health Administration has published safety regulations relating to air receivers, which in many cases correspond to the ASME standards, under the following codes: