Radium Adjustable Boost Pressure Switch, 3-15 psi Hobbs Type

Radium Engineering Adjustable Boost Pressure Switch, 3-15 psi, 1/8 NPT - Part #20-0236

A second fuel pump that runs all the time is a pump that heats the fuel, drains the battery at idle, and wears out for nothing. The right way to stage it is to switch it on with boost, and that's what this is: a normally open Hobbs-type pressure switch that closes at a set point you dial in between 3 and 15 psi, so the second pump kicks in when the turbo does and shuts off when it doesn't.

What It Is and Why It Works

The switch body is stainless steel with a 1/8 inch NPT male port; tee it into a manifold pressure source and the diaphragm inside closes the contacts when pressure passes the set point. It's normally open and only responds to positive pressure, so it does nothing at idle and cruise vacuum. The set point is adjustable across 3 to 15 psi, and it ships uncalibrated; you set it with a pressure source following Radium's instructions, which means you can put the second pump on at 5 psi on a small turbo or hold it to 12 psi on a car that only needs it at the top. The contacts are rated for under 0.5 amp, which is enough to trigger a relay and nothing more. The connector and pins are in the box, unassembled.

Specs

Fitment

Not vehicle-specific. On a K-series it usually goes on a spare 1/8 NPT port on the intake manifold or a boost tee; it can also trigger a water-meth pump, a warning light, or anything else that only needs to run under boost.

What to Know Before You Buy

Do not run pump power through this switch. It closes a relay coil and that's all; put 15 amps through it and you'll cook the contacts on the first pull. Wire it switch to relay to pump, with the relay fused off the battery. Calibrate it before you trust it: put a regulated air source on the port, watch continuity with a meter, and turn the adjuster until it closes where you want. Use thread sealant on the NPT, not tape shreds that can end up in the diaphragm, and mount it where it won't see exhaust heat. It only sees positive pressure, so it can't be used as a low-oil-pressure or low-fuel-pressure safety; that's a different switch.