Fuel pressure relief valve

[Jeepsinker]

Anyone happen to know what the opening pressure, and fully open pressure settings on the factory fuel pressure relief located on the secondary fuel filter housing is?
I finished my spin on filter setup and installed it today, used an aftermarket pressure relief valve recommended by Rustystud that I got from Murcal. Com. What I used is the "Prv 70" which has a crack pressure of 10 psi and a fully open pressure of 70 psi. My concern is that I'm only seeing 20psi at the final filter and it fluctuates. Pressure builds to 20psi, then I can hear the valve crack and my pressure drops down to 5 psi, then back up to 20, and so on. I did go for a six mile shakedown run and didn't notice any decrease in power or throttle response, but I am worried about starving my HH for fuel and destroying it.
It may just be that the 1/8"npt pressure gauge I got from Horror Freight just sucks that bad, but I don't have another way to verify pressure at this time.

At the very least a link to the TM section that lists the info I seek would be of great help.

 

[rustystud]

Anyone happen to know what the opening pressure, and fully open pressure settings on the factory fuel pressure relief located on the secondary fuel filter housing is?
I finished my spin on filter setup and installed it today, used an aftermarket pressure relief valve recommended by Rustystud that I got from Murcal. Com. What I used is the "Prv 70" which has a crack pressure of 10 psi and a fully open pressure of 70 psi. My concern is that I'm only seeing 20psi at the final filter and it fluctuates. Pressure builds to 20psi, then I can hear the valve crack and my pressure drops down to 5 psi, then back up to 20, and so on. I did go for a six mile shakedown run and didn't notice any decrease in power or throttle response, but I am worried about starving my HH for fuel and destroying it.
It may just be that the 1/8"npt pressure gauge I got from Horror Freight just sucks that bad, but I don't have another way to verify pressure at this time.

At the very least a link to the TM section that lists the info I seek would be of great help.

I would check out that valve. My pressure stays at 40 psi at idle and goes up to 60 psi at 2400 rpm. Maybe the filters are too low of micron also. Not flowing enough fuel. You should not have over 5 psi pressure difference between the filters. Mine are running at 3 psi pressure differential.

 

[gringeltaube]

Take a quick look here, on page 13.



G.

 

[Floridianson]

Yea I was bumping heads with Rusty on this one as I thought the pressure would have been higher than 60psi. I was going to do some testing but got side tracked and have never seen anything in a TM about the opening pressure. My thought was if the head needed 60psi to run at peak performance and flow fuel through it to help keep it cool but the secondary bypass opened at 60psi would the head realy see flow through or just have pressure standing waiting for discharge. I will try this week and test the valve as there is a motor sitting on blocks waiting for shipment out.

 

[lino]

Hey Guys,

I was checking out my PRV-70 pretty carefully when I was trying to duplicate in the filter setup I'm making. One thing I noticed (and didn't like) was that the capture screw that holds the spring and ball in place is threaded in, but only loosely. I was able to turn mine with my finger. That was adjusting preload on the spring, therefore cracking and operating pressure.

You might want to pull it off and thread that part in a little further.

Mine is handy, I can post pics if that helps

 

[Floridianson]

Yea post a pic of what you speak.

 

[lino]

Yea post a pic of what you speak.

Here ya go!



The second and third pics show the retaining screw in two very different positions. I suspect that the split in the screw should be "splayed" so that it retains its position with friction. Mine is not splayed and moves easily with my finger tip.

Here's the attached documentation:


Hope that's helpful.

ciao
lino

 

[Jeepsinker]

Yeah I noticed my retaining screw was flush with the end of the valve when I put everything together. I guess I should have fiddled with it, then I would have noticed it was loose. Looks like I'm taking it back apart and adjusting/ tightening that screw. Crap... Let me see if I can post a pic of my setup. It'll be upside down, so if a mod would flip it for me I'd appreciate it.

 

[Jeepsinker]

G, what I saw in the TM was that originally there was no pressure relief valve, only that the booster pump has a built in pressure regulator. So is it even necessary to have this pressure relief? I mean honestly these modern filters are rated to a minimum of 100 psi and have a steel core so they shouldn't collapse.

Thanks for flipping those pics for me by the way.

 

[gringeltaube]

I think that PRV at the top of the secondary is mainly a safety backup, in case the regulator on the transfer pump got stuck closed, to protect the system Also to avoid possible pressure build-up between that pump and the FDC, or- if by-passed- directly the HH, after engine shutdown.
Certainly an improvement over the early version shown in that TM.



G.

 

[Floridianson]

Yea if you look at the LDS boost pump there was no PRV in the secondary just at the Head and that boost pump made 80 psi going to the head.
My thought on the valve and our system was. The system on shut down is maybe 30 lbs. but goes to I believe 60 lbs at high idle. Our system has a type of PVR on the back side of the head but with a orifice drill through it so at all times there is a little pressure spill off to help keep the fuel moving through the Head for cooling and system clearing of air. Now if the PVR on the head was some how to develope a clog then the PVR on the secondary needs to open and allow for the problem.
I believe the PVR on the secondary's should not ever open at any pressure in tell it goes over the pressure we need at the head to run the best. I need to do the test I said I would. Bad puppy don't bark inless your ready to bite. I believe the PVR on the secondary's would only open at over 70 lbs and I mean not even a crack. As I said I will, this week test the PVR on the secondary's and see for myself if what I speek is speek or spit.

 

[Jeepsinker]

That would be very helpful. I did a "feel" test on the old filter base on my bench with a round punch today and it did feel quite stiff, which leads me to believe it has a pretty high crack pressure and an even higher fully open pressure. I thought before that this valve was to bypass pressure in case of clogged filters, since the originals had no internal reiforcement to keep them from collapsing.

 

[Jeepsinker]

I should add here that Rusty did tell me not too long ago that all Diesel engines need a pressure relief to refrain from damaging components on shutdown, so thanks to him I learned something that I didn't know before.

I just finished putting everything back together again. I removed the Prv, and found the retaining screw backed out just like was mentioned, so I finished removing it and decided to further shim the spring to raise the crack pressure. I used a small washer and E clip left over from an old four wheeler carb kit and got the feel of the spring where I was comfortable with it, but the valve still opens. I'm glad I decided to shim it because I still have got only 25 psi at idle. I'm sitting in the truck idling at 1000rpm right now to get up to operating temp before I run it up to 2000-2100 to see what my max pressure is going to be. I'm hoping for at least a good 58-60psi, since the TM calls for 65. I don't mind being only 5 psi shy.

Edit: Got 45 psi at 2000 and no more than 50psi at 2400. Guess that will have to do. If I shim the spring anymore the valve won't open.

 

[Floridianson]

I should add here that Rusty did tell me not too long ago that all Diesel engines need a pressure relief to refrain from damaging components on shutdown.

I can see that on some systems but ours. As I said our overflow valve on the Head has a hole on it to allow the fuel to allways flow through with the valve also insures that there is the correct pressure retained in the Head. To me our system can not build up over pressure on shut down as it as said flows through all the time to the return line. Yes I can see our secondary relief valve opening if the final fuel filter cloged and shut down. Then the pressure relief would open and it would seen if correct it could back flow and keep some pressure on the return line from the head and still allow fuel to reach the head and still maybe run well enough to get home. To me the secondary will not crack intill it sees at least over pressure. Yours cracking at 10 lbs to me would be incorrect. It should not crack till maybe 70lbs.
I am still trying to understand why some feel that our fuel system is not any good. With just a set of spin on filter bases you can get two 6 micron filters. Or just use the stock set up with a 10 micron filter in the secondary and a 6 micron filter in the final. I have some trucks that still have the same filters that came with the truck and run just as good as new. Our thick wall copper has lasted 30 years and inless smashed I fell good with it. I Don't think any rubber hose will last that long.

 

[Jeepsinker]

I agree. I'm going to keep the copper line as best I can. I have replaced all of the soft lines and plastic lines, but we all know they go bad over time. I'll see how this plays out with this pressure relief set the way it is. If I lose a HH then I'll just do away with the Prv and go from there. 25 psi at idle isn't terribly low though, only 5 lbs shy of what the TM calls for. I am now filtering down to 2 microns, but these are full flow filters so that shouldn't make much difference in pressure. I still get 4 psi to the final filter with just the in tank pump running, so I feel sure the filters aren't the issue.

And I'm still there with you on the Prv being there for bypassing clogged filters, hence it being inline before the filters instead of after the filters.

And I know filtering down to two microns ins to really necessary for our engines, but it makes me feel better about my fuel system and I have a feeling it will keep injector tip and HH wear down over time. I was also able to retain water drains on all of the filters.

 

[rustystud]

Jeepsinker, I think you got a bad PRV valve. Like I said earlier, mine has 40psi at idle then goes up to 60psi at 2400 rpm. As far as the Hydraulic Heads not needing a relief valve, that might be true in the older designs, but according to the later TM's I have, the Hydraulic Head doesn't have this hole. About the fuel lines. Mine where cracking due to vibration fatigue. So I replaced them all with PTFE Stainless steel sheaved lines and the return lines with DOT Poly (Nylon) hoses. These hoses will last long after all of use are in the grave. The PRV valve is actually installed between the filters, thus acting as a system relief not just a filter relief.

 

[lino]

I don't remember which TM I pulled this out of, but I found it exceedingly helpful to understand what was going on.


It even has a balloon on our particular subject here. Indicated as a fuel filter bypass. That shouldn't open until 60 or 70 psi.

 

[lino]

I don't remember which TM I pulled this out of, but I found it exceedingly helpful to understand what was going on.

OK, so that pic was from page 21 of http://www.steelsoldiers.com/upload/M35/TM9-2815-204-35.pdf which is for an LDS-427, immediately visible is the lack of FDC...

A similar, but not as clear pic can also be found on page 14 of http://www.steelsoldiers.com/attachment.php?attachmentid=465596&d=1385913114

Neither are directly applicable, but they get you close. I haven't been able to find this diagram for the LDT. If anyone has seen it, I'd be interested.

 

[Jeepsinker]

Well that is a G code pump in that diagram, same as mine. It also confirms that the relief does indeed open at 60 or 70 psi like Floridianson suggested.

 

[Jeepsinker]

I may open my valve back up and put one more shim in today. We'll see how I feel about it later today. One more should bump me up to 30psi at idle.