Backpressure bucking pump - need rheostat or return line?

[GeneralB44]

Hi all,
I have had several F150 style alchy pumps die on me, so I just bought a SHurflo. This thing pumps like a mad porn star!

The pump is smooth when jetting straight out of my 5/16" hose, but when I connect it to the nozzle (which isn't clogged), it starts to buck (turns on, then off - unsteady). The flow out of the nozzle is not misted b/c the pump can't keep a steady pressure.

I had two thoughts on how to fix this. Figuring there's just too much backpressure on the pump, I was thinking of either:

1. Wiring in a rheostat or something like that to run the pump at a lower voltage, to find a good equilibrium pump speed to keep a steady line pressure

2. Plumbing a return feed line after the pump outlet to relieve the pressure.

I would love any feedback or suggestions!
Thanks!

 

[blackbuick87]

Try a bigger hose to the nozzle
Many have used an F150 pump without this problem
My pump pumps 95psi (rated) without bucking

 

[GeneralB44]

Hi Bob,
I used to have that F150 pump (I have the Jay Carter kit too) and it didn't have that problem, but I never got a full spray pattern with it and it always made funny noises. Plus, 3 of those pumps died on me in a year! That's why I went w/ the Shurflo.

I bought a cool setup with a valve in the output line from the pump that should, when used with a tee in the line that I just hooked up to return excess flow to the alchy tank, allow me to dial in the pressure in the line to the nozzle... I'll let everyone know how it works!

 

[blackbuick87]

Sorry I misread your post
I was thinking you just went to a F150

Yes you are right a return line is probably the way to go

 

[cruzn57]

sureflo pump

does that sureflo pump have an internal regulator,?
that once it obtains a fixed pressure, it shuts off, then when the pressure drops, it resumes running,( surging, etc)
something to look at!
Of course a return line would eliminate this problem.
good luck!
cruzn57

I'm not trying to be a smart a$$, just helpful

 

[Bob Avellar]

A return line with a valve is a good way to go (check out my web site if you haven't seen it). The biggest advantage I have found is in the ability of the return(bypass) line to quickly bleed off pressure and flow from the nozzles once you let off of the boost. No problems with flooding the motor with excess, unburned alcohol. As far as the pump pulsating on/off as the limits of the pressure switch are reached I found that the atomization at the nozzles remained good. The actual flow rate does change as the pump cycles between the 2 limits but there should still be excellent atomization and good spray patterns from the nozzle(s) unless the pressure is too low. The standard 60 lb pressure switch should still provide good spray as it cycles but I opted for a 100 lb switch. Remember the switch is adjustable with a small allen key. Maybe it is set too low?

 

[GeneralB44]

I hooked up the return line (without the valve though, just to make sure that wasn't restricting the flow too much) and the spray pattern was inconsistent. Seems like it will spray a full pattern if I restrict the return line just enough so that the pump is about to pulse (once it pulses, it turns into water fountain type flow). I'll try again with the valve tonight.

Bob - thanks for the tip on the adjustable switch - I didn't even know about that!

Thanks!

 

[Bob Avellar]

My setup uses 2 oil burner nozzles (13 gph/hr ea if I remember right). These are the same type sold by carroll's Supercharging but I just buy them in a plumber's supply. My experience with that type has always been that they atomize very well even at pressures as low as 40-50 lbs. Obviously the volume of flow will change as well as the width of the spray pattern as the pressure alternates between the upper and lower limits of the pressure switch but the atomization always remained good. I realize your nozzle(s) are different so I don't know if they require a higher pressure to produce a good spray pattern than the ones I use. Just wanted to mention that we are using different nozzles. Over the years I have decided to let my pump hit the upper and lower switch limits since I never had any tuning issues that I was aware of that related to the pump pulsating. It seemed that the volume of atomized alky in the intake more or less equalized itself throughout the intake system. No indications of erratic flow through either seat of the pants testing or any info obtained with Directscan readings. The Bypass (for me) is now there for 2 reasons. One is to allow quick depressureization of the nozzles when I lift off of the gas and eliminate any driveability issues like flooding or stumbling due to alky still being injected under a low or no boost condition. The other reason I adjust the bypass valve so that the Shurflo pump still cycles on/off aproximately once per second is for safety reasons. Both stages of my system have a light on the dash associated with each stage. A green light illuminates whenever the pump is receiving power through BOTH an adjustable Hobbs pressure switch AND its OWN pressure switch that is built into the pump (actually it sits right on top of the pump head). A Blue light will remain lit whenever the solenoid to the second nozzle is receiving power through a separate Hobbs pressure switch. The GREEN light tells me that the pump is theoretically ON since it is getting power. However the pump could be bad and not run even though it has power to it. The key here is that the GREEN light will not be able to blink on/off at 1 cycle /second UNLESS THE PUMP IS ACTUALLY BUILDING PRESSURE. Now I could have 2 clogged nozzles and the light would still blink cause the pressure would still build- but it is likely that the cycling would occur at a faster rate since the only path for pressure reduction would be the return line. Also. if I notice that the light blinks at a slower rate than normal it allows me to check for things like a dirty filter (on the intake side of the pump), a leak, or maybe a pump going bad. I have replaced the pump head once due to slow pressure building as indicated by the light. The seals were swelled considerably by my use of Methanol but the pump head actually was working fine. I later found the cause to be a plastic filter with a SS screen had been softened by the methanol. This caused the nipple on one side to bend gradually and start to clse itself off! Please be careful with any plastic parts that you may have in your setuos especially with methanol. Some plastics will soften more than others. The filter that I use is also from Carrol's and I continue to use one. It took about a year for it to change shape and collapse. It is a clear plastic one with a screen in it. Hope this helps a little.

 

[GeneralB44]

Hi Bob - which direction increases the pump pressure? Any idea how many turns equals how many psi? (I turned it about 6 turns clockwise and it seemed to increase the pressure a bit). I seem to be getting a much better spray pattern after adjusting the pump pressure, using a shorter braided hose to the nozzle, and hooking up a ball valve in the line to the nozzle.
Thanks!

 

[Bob Avellar]

I am only about 98% certain that turning the set screw clockwise when viewed from above will increase the pressure setting. Screwing it further INTO the switch housing increases the pressure as far as I recall. I don't know how many turns equals how many lbs.

 

[GeneralB44]

Well, I got it hooked up with a nice, fine, consistent spray after some tweaking of the pump pressure and constriction of the return line. I went for a test drive, and WHOA!!!!!! This thing pulls waaaay harder than I remember when I had the F150 pump and could only run 18/19psi without knock. (I still only have a 20psi boost gauge, so I'm keeping the boost under that mark for now). Good stuff! Thanks, everyone!