odd pressures

[twent]

running a raptor 150 pump and when running on diesel pressure will be fine around 30psi, then switch to veggy and it will do 25 28 but as it continues to run on vegy after about 5 minutes the pressures slowly goes down to 10 psi at idle, then when purging pressure on diesel goes back to 30. after awhile i would go back to vegy and the pressure would be back up to 25 then goes back down to 10 after awhile.

i am stumped on this one.
pressure is taken at injection pump.
system is routed with supply from veg tank to valve to pump to valve to filter to line, heat exchanger and injection pump

[pquevill]

sure it is not a clogging filter or pick up screen/ That's what mine does when pressure drops, filter is clogging
Q

[twent]

new filter in place, and if it was the filter it wouldnt clog then unclog after then clog again like it is. prescreen is fine as well.

[DieselBurps]

The WVO is not feeding in fast enough for the pump to maintain pressure. It's hard on the pump to let this continue - it'll be pulling a lot of amps and you may burn it out.

You are pulling a thick, high-viscosity liquid through thin lines and multiple obstructions. If you don't have that liquid hot enough to flow like diesel, it probably won't flow like diesel... You can fix this problem by either getting it hot enough to flow like diesel, using thicker lines and reducing the obstructions. Think of it as sucking jello through a cocktail straw. Swap out that straw for a 7-11 "Big Gulp" straw and it'll get a bit easier. Melt that jello and it gets even easier.

Just for fun, try putting a 20% mix of diesel into that WVO before switching. Mix well and see if that pressure comes up. The decreased viscosity will most likely allow the pump to pull the fuel through more easily and maintain pressure. It's not a permanent fix, but it does confirm that you need to do something to allow the WVO to flow better.

[twent]

its plenty hot when it goes in cause it will circulate for about 5-10 minutes before going down to 10psi. plus it goes directly from tank to valve, and pump within 2'

[DieselBurps]

Originally Posted by twent

its plenty hot when it goes in cause it will circulate for about 5-10 minutes before going down to 10psi. plus it goes directly from tank to valve, and pump within 2'

And yet you still lose pressure. Nothing you have said takes away from my suggestions. You'll find that if you have a small pool of liquified jello, you'll be able to suck it through the cocktail straw for a little while before you hit the blockage. It gets worse if you get some PHO in the tank - or the jello.

Speaking of the tank - what are you using? A little polymerization near the tank pickup can make for some fun problems with the pressure. It comes, it goes - if you have a pickup screen that clogs, you may have a pool of fuel that gets picked up before the clogged screen slows the flow down. I have experienced that - and had to clean out the tank to fix the problem. You may need to put a vacuum gauge in line and trace through your system, bypassing one component at a time until you find the problem. Have the pump dump out to a container and spend some time isolating the problem. Definitely report back what you find.

[GreaseStudent]

Check tank vent first.

[twent]

vent is good, and there is no clogging of filter and the straw thing would happen much quicker then it is and has run for 40000 miles without problems. if there was a blockage somewhere it wouldnt be a gradual steady pressure drop over a 10min period and wouldnt clear up immediately after switching back for a minute.

everytiime i have had an issue with clogging the screen or the filter it never jumps up to normal pressure once clogged

[DieselBurps]

Originally Posted by twent

if there was a blockage somewhere it wouldnt be a gradual steady pressure drop over a 10min period and wouldnt clear up immediately after switching back for a minute.

Why not? Think about it if it is only a partial blockage, not enough to stop the flow - but enough to restrict the flow. How do you think the pressurized side of the pump would react in this case?

It's not a hard problem to figure out.

[newshop2]

Are you sucking a hose flat?