SEAFLO 42 Series 12V 4.0GPM 55PSI Water Pressure Pump Marine RV

12V automatic 42 Series water-pressure pump

The SEAFLO SFDP1-040-055-42 is a compact self-priming diaphragm pump for automatic onboard water supply. Its built-in pressure switch starts the motor as an outlet opens and stops it at 55 PSI. Internal bypass technology allows small flows to recirculate within the pump head, reducing rapid pressure-switch cycling.

Suitable boats, vehicles and systems

• 12V motorboats, sailing yachts, cruisers, fishing boats and houseboats supplying galley taps, basins and showers from a water tank.
• 12V motorhomes, caravans and remote cabins requiring an automatic demand pump.
• Suitable where 15.1 LPM open flow, 55 PSI shut-off pressure, 13 A circuit capacity and 1/2-14 MNPT connections match.
• Can serve several outlets, but simultaneous performance depends on pipe bore, lift, restrictions and fixture demand.
• Not a bilge, fuel-transfer, sewage or macerator pump.

Verified technical specification

Compatibility and installation checks

• Confirm a 12V DC supply and size the fuse, switch and cable for the 13 A maximum draw.
• Confirm the 1/2-14 MNPT ports and ensure all hoses, taps, heater/calorifier and fittings are rated above 55 PSI.
• Install the inlet strainer and flexible connections stated for the configuration; mount in a dry, ventilated, serviceable position.
• Protect the pump and plumbing from freezing and sanitise the complete system where used for domestic water.
• Run-dry capability does not justify deliberate extended operation with an empty tank or blocked inlet.
• Package: one SEAFLO 42 Series pump. Verify the photographs for included strainer/connectors; hose, fuse and main wiring are installation items.

Frequently asked questions

Does it switch on when a tap opens?

Yes. The built-in pressure switch starts and stops the pump automatically.

What does the internal bypass do?

It allows small flows to recirculate inside the pump head, helping reduce rapid pressure-switch cycling.

Can it replace any 12V pump?

No. Compare current, flow, pressure, port thread, dimensions and the ratings of every plumbing component.

Can it be used as a bilge pump?

No. It is a pressurised-water demand pump, not a submersible bilge pump.