For many small compressed air users, the question of where to place the receiver tank in their system comes up frequently. It’s often taken for granted but the tank performs several vital functions and is worth talking about.
The size and placement really depends on what you need the tank to do:
- Remove liquid moisture formed at the discharge of the compressor.
- Provide a cooling zone to allow moisture vapor (and oil aerosols) to condense into liquid.
- Create a volume buffer that reduces compressor cycling on and off.
- Provide volume for users that are not getting stable air supply or for large, periodic demands that exceed the capacity of the compressor.
- Reduce compressor run time and save energy.
Most of the time, the receiver tank is very close to the compressor. Often they are sold as one unit. This helps reduce total run time and frequent starting and stopping, saving some energy and also reducing wear and tear on the compressor. In the compressed air business, this tank is sometimes called a “wet tank” since it collects a lot of liquid. Putting the wet tank a bit further away lets the air cool and more moisture condense before you drain it away, but whether you put some distance between the compressor and tank or not, the wet tank should be before the dryer. This reduces liquid load on the dryer and its drain. If you have a properly sized refrigerated dryer, it’s unnecessary to try to put distance between the compressor and tank.
If you place the wet tank away from the compressor, be sure not to undersize the piping between them or you will have high pressure drop and cause the compressor to short cycle (start and stop too much). Additionally, you will get water in the line before the tank so be sure to install a good automatic drain on the tank and avoid any upward slant in the piping to the tank to prevent water from collecting at/in the compressor. Tanks have multiple access points, and it’s a good practice to pipe in low and pipe out high if possible (see diagram below). Piping in high and out high is also okay.
“Ideal” textbook systems have both a wet tank (to control cycling and drain moisture before the dryer) and a larger dry tank after all the dryers and filters for storage. This is widely recommended in industrial settings, but for smaller systems it is not common for cost and space reasons.
The key is the order of the system and for most small compressed air systems the order below is appropriate:
- Tank with automatic drain valve (pipe in low, pipe out high)
- Refrigerated dryer with automatic drain
- Coalescing oil filter with automatic drain
- Spray booth dryer (membrane or desiccant or breathing air system) if desired.
Note that in this arrangement, a “wet tank” is selected. This is because most smaller shops are concerned about moisture removal. When placed after the compressor, the tank serves to separate a large part of the moisture that naturally occurs during the compression process before the air enters the dryer. While dry tank storage is helpful, it is typically not as important as moisture removal.
The green piping shown in this diagram takes the condensate from the tank, dryer, and filter into a condensate separator.
If you have issues getting a stable supply of air to certain areas, but your compressor is large enough, consider installing an additional tank near those points of use.
If your installation has special needs, consult a compressed air systems specialist for assistance in designing your system layout. In addition to making sure your system will give you the air quality you need for your shop, they can take into account any special considerations you may have.