Low (fuel) pressure switch that closes at <= 5 PSI

[Angelo]

This is for a 1996 6.5L TD ambulance which weighs approx. 12,500 lbs.

Currently using a 1993 lift pump and have been happy with the higher pressure, but I want more. Right now idle is 9-10 PSI but it will drop down to 1-2 PSI at WOT.

I plan to have 2 lift pumps inline. One will run constantly and the second will only turn on when fuel pressure drops below 5 psi or so. I can wire a switch to turn the second one on but I know it can be automated.

So I'm looking for an inline fuel pressure switch that will turn on when pressure drops below 5 PSI or so. The purpose is to turn on a second inline lift pump so I get that additional fuel pressure when giving more throttle is necessary climbing hills.

I've seen options out there like this. But can't figure out at what psi does the switch turn on or off. Anyone have any experience running 2 stock lift pumps inline or using a pressure switch like that? They're used for water applications as well.

I won't consider spending $$$$$$$$ on a fass or airdog. That is way too much money for just a pump and filter IMO. Just a shortcut to a custom solution for higher psi that can really be achieved for less than $90 total.

 

[Erik the Awful]

I've seen options out there like this. But can't figure out at what psi does the switch turn on or off.

That's a valve, not a switch. Apply 12v and it opens.

You need something like this. Note that it's a NC switch, meaning that it will supply power to the pump until it reaches 5 psi.
www.amazon.com/DVPARTS-Pressure-Switch-0L2917A-Generac/dp/B0967KZLC5

 

[Angelo]

That's a valve, not a switch. Apply 12v and it opens.

You need something like this. Note that it's a NC switch, meaning that it will supply power to the pump until it reaches 5 psi.
www.amazon.com/DVPARTS-Pressure-Switch-0L2917A-Generac/dp/B0967KZLC5

That seems to be the answer I'm looking for. Thanks!

 

[Angelo]

Does anyone know how a NC OPS with 2 terminals works? Does that just mean there will be continuity between the contacts when "closed" and then once open, continuity is lost?

 

[Erik the Awful]

With no oil pressure, the switch will have continuity. Once the engine is fired up and oil pressure rises, the contacts open and lost continuity. For the circuit you described above, it's the appropriate switch.

 

[yevgenievich]

Or add a switch to the pedal