We have fielded several of these “sputtering calls” recently. In most cases, the customer tells us they think they are getting air mixed with their paint impacting fluid flow. Yes air can get into a paint line even with a closed-loop system, such as a pressure pot.
The most common cause of pressure feed lines sputtering is a variation in tank pressure because paint has migrated into the pressure pot regulator or plugged the passage below the regulator. Sometimes the cleaning of the passage or regulator is all that is necessary to fix the problem. Other times the regulator needs to be replaced because the paint build-up inside is preventing the diaphragm or poppet from operating properly.
The second most common cause of pressure feed paint sputtering is a restricted pick-up tube, and/or plugged paint hose. The tube can be cleaned and the hose needs to be replaced.
The least likely cause of pressure feed paint sputtering is an air leak where the pick-up tube screws onto the fluid outlet fitting on the tank lid. With the top of the tank pressurized with a head of air it is understandable how air can migrate into the top of the pick-up tube and out to the gun. Reseal this connection with a thread lock product and let it stand overnight before using the tank again.
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