An air receiver, sometimes referred to as a compressed air tank, is an integral part of any compressed air system. The main purpose of this is to act as temporary storage to accommodate the peaks of demand from your system and to optimize the running efficiency of your plant.
Your air compressor installation can in theory run without a receiver, but not having one in your air system can increase the loading and unloading cycles on the compressor making the compressor work harder. It is important to remember that load/unload cycles will depend on the demand fluctuation within your facility. Air receivers, commonly referred to as vessels or tanks are used to store compressed air before it enters into the piping system and or equipment. In simpler terms, air receivers act as a buffer mechanism between the compressor and the fluctuating pressure caused by the changing demand. Some air compressors can be "tank-mounted", which means that they come as a package and are mounted on top of the air receiver. This type of a set-up is highly preferred at facilities where space comes at a premium. Having a tank mounted compressor can save on both space as well as initial installation costs associated with commissioning a stand-alone dryer. This is most commonly seen with smaller range compressors, mainly up to 26kW or 35 HP. Larger air compressors are not suitable for tank mounted option, as they become top heavy and could pose a safety risk.
When it comes to sizing of an air receiver, a good rule of thumb to remember is to allow 3-4 gallons for each CFM or 10-15 liters for each liters/second of compressed air depending on the type of an air compressor used and the application. Similar to sizing of an air compressor, there are a number of factors that should be considered in identifying the right size of air receiver for your installation. It is highly recommended to consider the following factors:
1. Minimizing pressure fluctuations/drops: An air receiver can be used to minimize pressure fluctuations that could have an impact on the production process and the quality of your end product. Selecting the right air tank for your compressor requires you to be mindful of two values: your compressor's output pressure and what your application needs at the point of use. Note that the compressed air stored in your air receiver is only useful as long as its pressure is sufficient for the process which uses it. This is why it is important to consider the duration (in minutes) that the air receiver can supply air at the necessary pressure for your end-user / equipment.
2. Meeting short term peak air demands: If the demand for compressed air changes drastically throughout the day, it is important to account for the spikes in the demand to ensure the system pressure does not drop below an acceptable level. An air receiver provides storage to meet short term peak air demands that the compressor cannot meet. Depending on the time of day, the shift pattern or even unusual demand (e.g. occasional use of a sandblaster or an abrasive media blaster), your air requirement may vary. It is important to fully understand the application and the amount of CFM or liters/second of air required, as well as the expected peaks of your system, as it dictates what flow of compressed air is needed to avoid shortages for any part of your process.
3. Energy considerations: Using an air receiver can help reduce energy consumption of your compressed air system by enabling load/unload (fixed speed) compressors to operate on a longer cycle and with tighter pressure bands. Having properly sized tank and more air than is required will reduce the potential of trim compressor starting up to meet increased flow demand, which can have substantial savings on your energy consumption. This will also prevent pressure fluctuation and frequent motor starts, while providing steady pressure and extending the life of the compressor.
4. Safety considerations: If needed, an air receiver will provide a supply of air to enable production processes and systems to be safely shutdown in an emergency situation.
You might have heard it already - a higher pressure in your air receiver would mean more air for your process and tools, so you would not need to buy a larger compressor even if your demand increases overtime. This statement is not true and the pressure of your tank should be related to the output pressure of your compressor. Most standard fixed speed and variable speed drive compressors can deliver compressed air at up to 175 psig (12bar), however, majority of industrial facilities operate between 100-125 psig (7-8 bar). Depending on your facility's needs, the air receiver’s maximum pressure should be sized accordingly. For example, if your fixed speed compressor is rated to deliver maximum of 125 psig (8 bar), the air receiver should be rated at the minimum of 150 psig (10 bar). Most variable speed drive (VSD) air compressors are rated up to 175 psig (12bar), therefore, a 200 (14 bar) psig air receiver would be more suitable in this type of compressed air system. Each air receiver should be equipped with a pressure relief valve, which is designed to release pressure from the tank in case the tank reaches its maximum allowable pressure inside the vessel. It is important to remember that higher pressure does not equal more flow (CFM or l/s), but just the opposite, as we raise pressure, the flow decreases. It is very important to understand minimum and maximum pressure settings for the machines that utilize compressed air and if possible use pressure regulators out of the air receiver and or at point of use. A good rule of thumb to remember is that each 2 psig is equal to 1% of energy being used (1 bar is equal to 7% of energy), which means that we should keep our system pressure according to facility’s needs, in turn resulting in further energy savings.
Although, some might be tempted to take on a DIY task of building your own air receiver, it is not a commodity that should be self-built. Due to extreme potential of safety risks and legal regulations. Air receivers should always be purchased from a reputable air compressor manufacturer or a professional pressurized vessel builder. It’s best to reach out to your local compressed air expert for advice and suitable solution for your compressed air needs.