Vent Valve is used with FL Series Injectors to relieve system pressure back to reservoir after a lubrication cycle. With a pneumatically operated pump, air pressure would be applied to the Vent Valve at the same time air pressure is supplied to the pump. When air pressure is relieved from pump and Vent Valve, lubricant moves past the valve seat and out the vent port. Normally, this lubricant would be piped back to the pump reservoir.