Four chamber design for smooth flow at all demand levels. No rapid cycling. Designed and built specifically for the harsh marine environment, they are dry self-priming up to 6' and can run dry without damage. Featuring sealed motor and pressure switch in a seamless, E-coated housing for superior longevity. Ignition protected, thermal breaker. 2.0 GPM pumps handle 1-2 fixtures, larger pumps handle multi-fixture installations. Includes fittings (swivel straight adapter 1/2-14 NPT x 1/2" barb (Qty. 2).4138 Series are direct replacements with same mounting bracket as Aqua King 3901.