WHAT RATIO PUMP SHOULD I USE FOR MY AIR ASSIST AIR GUN?

The answer depends on the required working pressure.

For the sake of this discussion, let us assume we need 700psi. Diaphragm pumps are 1:1 ratio pumps, so that leaves us with a 2-ball piston pump. Let us also assume that piston pumps have a maximum inlet pressure of 100psi. That would leave us with a maximum pressure of 700psi for a 7:1 pump.

At 100psi in, a 7:1 pump would build up to 700psi and stop (commonly called stall). Let us simulate a spray gun fluid nozzle of .001". We will put a plug in the fluid outlet of the pump and drill a .001" hold in the plug.

At that point, the pump would be delivering close to the maximum pressure of 700psi, but very low delivery. Next, we change the hold to 1/8". We will get more delivery but less pressure. As we continue toward the fluid outlet plug, delivery will continue to go up while pressure continues to drop.

There is a point that allows adequate fluid delivery and pressure. Typically, that would be somewhere in the neighborhood of 60%. In our example situation, achieving 700psi of working pressure would require a pump capable of approximately 1200psi or about 12:1. Sixty percent (0.60) multiplied by 1200psi yields 720psi.

Fluid delivery to match the application would depend on the application required flow and the delivery per cycle of the pump fluid section. Try to size the pump so that the flow per minute is achieved in approximately 15 cycles per minute. Your pump and maintenance department will thank you.

If you want more information, please contact your Diamond Distributor or Binks/DeVilbiss Tech Support at 800-992-4657.

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