Pressure testing, air versus fuel?

Wondering how accurate testing fuel pressure regulators on the bench with air would be?

I've been using this to set up Injector Pods with serviced injectors, stock regulators converted to adjustable with new springs and set fuel pressure before installing them on a vehicle. With a known pump the pressure on vehicle is always spot on! So it's a good tool. But wondering how far I could push it for testing springs and accuracy?

One thing I learned about air as pressure and testing different springs! You can hear the regulator flutter when pressure in is in range of spring pressure and adjustment of regulator! It does not flutter and make noise if fuel pump pressure is higher or lower then spring capability's. The regulator is either stuck closed when not enough pressure to open regulator and fuel goes through bypass, or regulator is blown wide open if it's not strong enough for pressure. Either way there is little to no adjustment from regulator at these highs and lows.

I just finished buying a digital spring pressure tester for checking springs when building cylinder heads.
Before that I just a bathroom scale and drill press (when compared to a spring pressure tester it was within 5lbs).
i've not tried using air to test springs,but since yours are so small with little spring pressure you should be able to rig something up using a postage scale to compare.
just make sure when comparing that you compare at the same heights.
HF sells a nice little digital scale I use for small stuff that is cheap.

not sure on the air versus fuel though.

i wonder if air's characteristic of flowing much easier than fuel is what is causing the flutter? air moves rapidly enough to where the diaphragm basically overcompensates its opening and closing action?

I don't know? But you can sure tell when it's working. Never heard a peep out of one on a vehicle. What's cool is your thinking "this pressure is way to much for this spring?" Sure enough, no flutter, it's blown wide open. Pressure you get is what ever pump puts out... well even if regulator is blown open it does have a small effect on pressure.

How much air pressure are you using?

Air goes into a regulator so I can set it for any pressure that a pump is spec for. Gauge on right is pressure coming in and gauge on left is Fuel Pressure.

http://www.gearhead-efi.com/Fuel-Inj...8&d=1397443203

I made a similar set up but I'm not just getting consistent results. Seems I have to have a lot more inlet air pressure than fuel pump spec pressure in order to achieve what a known spring should make pressure wise. May need to look for restriction in my fittings...

Do you ever get the regulator flutter?

The regulator I'm using is OLD and sometimes it will slip off and air just passes by. See the rubber mallet in picture? That to give the regulator a whack and it centers the regulator again and works. I think it slipping off may be from air instead of fuel? Or it being old. I've also found the tighter the spring the more sensitive it is to this.

Using the 2 long studs that come in a regulator kit really helps get the spring compressed and all together straight. Use them in the 2 holes that do not have pins to hold regulator gasket in place, then it's held in place in all four corners.

Next step I was thinking about is like a 1-2 gallon fuel cell to mount each pump and run gasoline. Lot of money to set all that up though.

But when I test at 30PSI which is late BB 7.4L EP377 pump with gold spring (pressure in that range) results are great and when installed on vehicle pressure is still spot on! This combination yields adjustment from top to bottom of screw in regulator spring can, nice big wide range 18-26. With the wide range of operating pressures I think the spring matching the pump is more important. Like a stock spring and one of the high pressure pumps with adjustable regulator makes no change in pressure either all the way up or down. The regulator is just blown open.

Air will not be a reliable way to set fuel pressure regulators, the way each fluid (air and fuel, air is considered a "fluid" when talking about flow through a restriction) is quite different.

There is a fluid that has the same properties as fuel, without the flammability. It would require a full test set-up, that includes a fuel pump and fluid return to reservoir, but would be reliable.

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Originally Posted by EagleMark

Do you ever get the regulator flutter?

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Yes I also got flutter, but when the air pressure was too low. One thing to consider, is although the pump maybe rated at XXpsi and XXlph it will dead head considerably more pressure. Knowing what that pressure is might be more helpul. A vortec pump will maintain 55-60psi yet dead head over 100psi. Regulating the air down to working pressure cant be accurate.