Air bubbles in the fluid line
Coaxial: In a spray system with coaxial tubing, the fluid and air run separately from the pump to just before or at the nozzle tip, where they are mixed. There should not be any large air pockets in the inner tubing carrying the fluid during normal operation. Air pockets may be present after initial setup, rebuilding of a pump, the pump stack has been disassembled for service, or if the fluid reservoir has recently run dry. This should only happen for a short time until the air has been worked out of the pump. If constant or consistent large air pockets are present in the fluid line, the pump may need to be rebuilt or replaced.
Single Line: In a spray system with single-line tubing and a pump equipped with an air metering screw, the fluid and air are mixed and travel together through the tubing to the nozzle tip. The air metering screw must be open and properly adjusted so the air can push the fluid through the tubing and out the nozzle tip.
Oil Only: In a spray system with single-line tubing and an oil-only pump, there should not be any large air pockets in the tubing carrying the fluid during normal operation. Air pockets may be present after initial setup, rebuilding of a pump, the pump stack has been disassembled for service, or if the fluid reservoir has recently run dry. This should only happen for a short time until the air has been worked out of the pump. If constant or consistent large air pockets are present in the fluid line, the pump may need to be rebuilt or replaced.
It is not uncommon to see very small air bubbles (around .010” or smaller) in the fluid as it exits the pump. This can result from the agitation of the fluid within the pump and forcing it through the outlet check valve housing in the pump. The existence or amount of these very small air bubbles can depend greatly on the fluid being pumped by the system. These small air bubbles do not necessarily indicate a problem with the pump or its operation, but they can collect at high points in the fluid tube routing and combine to form larger air pockets. Attention to the fluid tube routing to eliminate high and low points and give the air bubbles a direct path to escape out of the nozzle tip will greatly reduce these air pockets from collecting over time.