The air valves should be so arranged that they may be removed without breaking the water joint, and be so arranged that they may be taken out and replaced in a few seconds.
The main tank must be provided with safety valve drain cock and pressure gauge, and the air main, of not less than ¾ in. diameter barrel, preferably steam barrel, must be arranged to travel in a downward direction from the main tank towards an end station tank, which is a duplicate in miniature of the main tank or receiver. All branches must be taken upwards off the main. Such an arrangement, if care is taken that the end station tank has its relief valve set to blow off before the main tank safety valve acts, ensures that all moisture is collected in the end station tank.
The Airostyle and Lithos, Ltd., claim to be the originators of such a system, and it is here explained in print for the first time.
All experiments with a view to scrubbing or purifying the compressed air of moisture, oils, etc., on the air main side of the main tank, other than the above simple expedient, have proved more or less failures, either from want of appreciation of the increased capillary attraction set up in the tanks and air main, or from the difficulty of satisfactorily and frequently cleaning out such scrubber as may be inserted, and the incidental difficulty created in the prevention of dust being carried out of the scrubber throughout the system.
It need hardly be said that ample air must be provided in order to have sufficient pressure always available for the full number of operators employed, and this point is one which cannot be too strongly emphasized, for in too many cases firms have installed small compressors and have been misled as to their maximum capacity, mainly through over anxiety on the part of the salesman to secure his order for apparatus, he apparently having been afraid to ask a high figure for a really efficient compressor.
Another point of importance is that unloading devices, cutting in and out automatically should be avoided at all cost where compressed air is to be used for painting. The reasons are that it is much better to use the surplus air for the purpose of getting rid of the condensation in the way already indicated, and that in addition most unloading devices are in the nature of compromises, and while saving only a small amount of power materially increase the wear and tear by throwing the load in the reverse direction on the gudgeon pin, large and small end of connecting rod and main bearings, and by causing a hammering action to be set up.
This applies in particular to air compressors with automatic valves where the device works by means of a valve closing the air intake entirely, and so setting up a vacuum in the cylinder.