Air but no fluid out of nozzle.

2021-02-16

By Kevin

Initial Troubleshooting Information:

General Operation: The Unist metering pump is a pneumatically operated positive displacement pump. It requires an adequate air pressure source to properly operate the pump. Pumps can be driven by a pulse generator (PG) which cycles the pump at an adjustable rate as long as air pressure is applied to the system, or an OR element that strokes the pump once every time air pressure is applied to the system. There are two style pumps: Standard and MV. The two style pumps look different, but operate on very similar principles.
Air Pressure: The pumps need a minimum of 60 psi to operate properly. 80-100 psi is preferred. Less than 60 psi supply pressure to the pumps may affect cycle rate (pulse generator driven pumps), the pump’s ability to stroke, and/or how quickly the pump can be cycled. Reduced air pressure can also reduce air output at the nozzle tip.
Fluid Pressure: Most pump based systems are gravity fed from a reservoir at atmospheric pressure. If a system is fed from a pressurized tank it should have an air trap on the top of the pump stack. The air trap requires occasional maintenance to ensure proper fluid level. Pressurized fluid fed to a pump stack should typically be set at 5-10 psi. Fluid pressure should never exceed 10 psi.
Fluid Delivery: Fluid and air are typically delivered to the nozzle via either a coaxial hose or a single line. In a coaxial setup fluid exits the pump and (typically) into 1/8" OD nylon tubing (capillary). This tubing carries the fluid inside of a (typically) 3/8" OD polyurethane tube which carries the atomizing air. The air and fluid are kept separate until they are brought together at the nozzle tip. The capillary is spliced together at the nozzle inside of the black aluminum nozzle coupler block. The splicer on a Coolubricator^™ has a small hole in it to help with consistent oil output from the nozzle. The splicer on a Serv-O-Spray^™ does not have this hole.
In a single line setup the fluid and air are mixed at the pump outlet and travel together all the way to the nozzle.

No fluid output from the nozzle tip can be caused by a pump that is not pumping fluid either because it is out of fluid or there is an internal problem. No fluid output from the nozzle tip can also be caused by an issue with the capillary line that carries fluid from the pump to the nozzle tip or its connections. Follow the troubleshooting flow chart below to determine the root cause.