Air Tank for Compressor

G'day Peter,
Perhaps some understanding of the physics involved may help you sort this.

Atmospheric air always contains some water in vapour form. As the air is compressed its volume is reduced but the water content remains until the air becomes saturated and further compression causes some of the water vapour to condense into liquid form and 'drop out' of the compressed air. This action is compounded by the temperature of the compressed air. As it is compressed its temperature rises and it can support more water in vapour form but as the air cools the vapour condenses into liquid water.

Typically, in an air compressor installation, the air leaving the compressor is hot and supports the water in vapour form but as it cools, either in the piping or in the receiver, some water will condense and become liquid in the pipe or receiver.

It is usually easiest to drain this collected water from the bottom of the receiver so the system is arranged so that the compressor is above the receiver (look at all the portable sets) with a drain in the bottom of the receiver. Piping from the compressor should fall continuously from the compressor to the receiver without dips to avoid water collection in the dip.

If the compressor is below the receiver and some cooling takes place in the piping then water will drain back to the compressor. Air will bubble through this collected water until the compressor stops whereupon it may drain into the compressor which is most undesirable. If the compressor must be mounted below the receiver then a water trap needs to be incorporated at a low point following the compressor with either an automatic drain or with sufficient volume capacity to enable a manual drain.

It is also possible to mount the compressor below the receiver if the discharge piping or hose is thermally insulated so that minimal condensation will occur in the hose and connect it to the top of the receiver tank. Cooling and condensation will then take place in the receiver and can be regularly and manually drained from the bottom of the tank.

Hope this helps.

Peter....In a theory point of view you're correct BUT in real life especially with a small air compressor on a vehicle the chances are unlikely.

The way to avoid and how most are done is to run the air inlet and outlet on top of the tank with a drain point on the bottom.

If you want to stop condensation entering the tank you could run a water trap.

Peter why do you want /need a air tank, What will you use it for.

Peter, one convenient reservoir for compressed air that you may have forgotten, and you already have on board, is your spare tyre(s). Inflated to 60 psi they hold quite a bit of ready air for blowing, tyre inflation etc Best of all they can be inflated at a servo. A single tyre at 60 psi will inflate a completely flat tyre to 30 psi in seconds.

Bob