kawi600

I converted my truck to run veggie oil over the last few months. This involved replumbing some stuff and changing the order of the components. Initially I had no problems but now Ive got air leaks someplace.
The stock order is heater-liftpump-filter-ip, now its heater-filter-liftpump-IP. The thing thats worrying me is that the fuel filter that was under pressure is now under vacuum and I dont know if its rated for vacuum, especially the drain on the bottom. Ideally Id like to lose the thing in favor of something with the ability to run 1/2" (or at least 3/8") push-lock fittings since I upgraded the fuel lines to 1/2".
Anyone know if the stock filter and drain is rated for vacuum? Any ideas on what I could replace the filter assy with thats good for the vacuum and flow rate on this truck? I have no idea what the flow rate even -is- on the mechanical pump'ed cummins, but I know the pump will push fuel to around 40psi max, whatever that is in vacuum on the other side. Not knowing the specs is making it hard to look for alternate setups.

infidel

The way the drain plug is constructed it wouldn't hold well at all under vacuum. Pressure forces it closed, vacuum would suck it open. The drain valve thread size is the same as a commonly available autoparts oil drain plug. You could plug it up but then you wouldn't have a drain.
Also beware that the fuel heater/prescreen isn't designed for pressure, just suction.

One thing I'm certain about from hydraulics design is that a filter on the suction side of a pump is never recommended, it can cause air that's entrained in the fluid to be sucked out causing bubbles. It's due to causing a negative pressure differential across the filter media. All fluids contain air even if you can't see it.

The stock filter is rated at 17 gallons per hour at a 5 psi maximum pressure drop.

schoust

Hey Kawi,I think you would be better off running to independent loops instead of using the stock lift pump I use a shurflow and a seperate filter and just loop it back to the veggi tank this way you eliminate all the air if any.And as far as the filter goes I use a heated fleetgaurd that I got off of some guy on E-bay,I still see these every now and then....

kawi600

Infidel, yeah thats what I thought. I purchased another drain assembly but I dont think thats going to solve the problem totally. I might hack one up so I can go to a screw type release. The other idea I had was losing the WIF and using another fleetguard filter with the drain integrated in the filter. I was also looking at different filter assemblies like the racor that said they were rated for vacuum.
It does have two seperate loops.. but the filter had to be put before the liftpump so the pump could deal with both liquids. Only other way I can think to remedy the problem is with an electric pump for the veg oil tanks, or check valves to go around the filter.