A pump's controls consist of an on/off switch and a dial to adjust the pressure setting. Unlike an air compressor, a typical pump has no pressure gauge to adjust to – with one exception, the top-ranked Airlessco (right). Pumps are usually adjusted by eye as the painter dials in just the right amount of pressure to deliver the most effective spray pattern for the viscosity of the paint and the size of the tip. Even though the pressure drops some when the trigger is pulled, the gauge can help less-experienced users start close to the correct pressure recommended on the paint bucket, usually around 2,000 psi for latex paints. Users get to know the relative dial position of their common settings, so the best dials have an easy-to-read scale attached; good examples are the dials on the Airlessco (right) and the Graco Ultra 395 (below, left).
The motors powering the pumps have a few important differences. Only the top-two-rated units detailed here have electronically controlled variable-speed motors, which maintain the pressure output more precisely than single-speed motors. Since there is no reservoir to hold pressure (the way a tank does on a compressor), airless sprayers pump only when the paint is flowing. Single-speed motors have to cycle on and off frequently to regulate their pressure; they switch between running the pump at full speed and not running at all. Depending on the quality of the pump controls, the lapse in pressure before the motor starts up again – called the deadband – can be up to several hundred psi with a mechanical switch and a single-speed motor. For the electronically controlled variable-speed motors, the deadband is the lowest, at 50 psi.
This valve switches between sending pressure to the hose for spraying, and circulating fluid through the pump and out the prime hose for priming or rinsing out the pump. We prefer the valve lever to be in a well-protected location, as it is on the Titan XT420 model (shown).
The master tech at our regional service center advises against the common practice of using this valve to release pump pressure (rather than bleeding pressure out through the gun). The sudden surge of intense pressure wears out parts in this valve prematurely.