Relief Valve Guts: Exposed

Amish Elegance

Amish Elegance

Schadenfreude
Joined
May 1, 2006
Messages
3,465
I've never seen this posted, so I thought I would.

Out of curiosity, I gutted my blown valve to cipher on how I might make it whole again.

After tweaking the helicoil slightly (seen far right) it spun right out. Then with a couple twists of an allen wrench the hollow plug spun out. I was expecting more whiz-bang.

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Innards.
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The needle valve responsible for holding all that pressure, normally anyway.
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Once it lifts, there's two holes that allow it to piss fuel pressure rather efficiently out the return.
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Crappy pic of the holes. Sorry.
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A Few shots of the body showing how the needle sits in the taper.
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Interestingly enough, Dual CP3's can make enough pressure even shooting through this hole to have a truck run ok. No codes, no nothin.
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***Fat Bastard Voice ***
"Whoa, ees tiny!"
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Everything stacked up as in the housing.
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If you haven't seen it, now ya have.

Can somebody explain to me what craps the bed and makes this thing worthless after a pop or two?

The only wear I can see is a little polish on the tip of the needle where it lifted on many occasions while I chased my tail figuring it out. :doh: The spring still has some boing to it, but I'm curious as to what causes it to fatigue after only one or two cycles?
 
Those parts are far to tiny for me to begin to cipher on......
 
I'm quessing the needle doesn't seat properly, or re-seat for that matter. Really thought there would be more to it than that. Looks fairly simple.

Curious though. Could a guy put some shims behind the spring and make a relief valve that opens at 30k psi instead of 26.5k psi?

Guess it wouldn't matter if you couldn't get the needle to re-seat every time.

Anyhow, thanks for posting the pics.
 
Fuel passing through those small passages at high pressure creates heat, enough heat to take the BOING outta the spring.
 
kalder said:
Fuel passing through those small passages at high pressure creates heat, enough heat to take the BOING outta the spring.
Click to expand...

That is it, the spring loses it and no more duty cycles from the spring.

John
 
Could something be made/altered on this that would let fuel return above say 27k and still function for a good length of time?
 
Nice work AE. Thanks for the pics. You're alright.:rockwoot:
 
Seems to me a few out there are shimming them, that would be a art, and a way of testing it would be handy. I'm putting a relief back one way or the other.

If I have to dump the throttle for some reason, or say by accident at the end of a pull, always hear this high pressure dump, and pop a high rail code.

Thanks for the exploaded view......
 
Snedge said:
Nice work AE. Thanks for the pics. You're alright.:rockwoot:
Click to expand...

Thanks for sending the one that replaced it. I may need another.:doh:


Spring is the issue, eh? Time to get some calipers, pin gauge, calculator, and a big thick freekin book.

For what's in these things, there really is no reason for them to cost like they do. Even at Jeff's cost, after seeing it I'm sure there is enough margin there to load up a junkie for a week-long bender with every one.


No prob Joe and others. I'd never seen one apart and decided boldly going where no one has posted before would require little effort. I really expected more fancy fangled pressure diaphragms or something made out of precious metal. ... that or enough spring pressure to fling something hard enough to take an eye out and make 'Holle-ween' a pirate ordeal from here on out.

I was disappointed. :(
 
My theory for what it's worth.... The way the valve is mounted to the rail (vertical), it becomes the perfect water trap. The water sits in the bore above the valve. Once it opens it no longers will slide back and seal as well. It doesn't take much of a pit to stop sealing 25K psi. If you look at the end of the valve, the seat in the bottom, and the side, under a microscope, you will see what I'm talking about. Ones that get really bad, the valve will actually stick enough open, that the truck won't even start, even with dual CP3's.

Paul
 
kalder said:
Fuel passing through those small passages at high pressure creates heat, enough heat to take the BOING outta the spring.
Click to expand...

Wouldn't the fuel decrease in temperature. Since it is expanding through a nozzle from ~26kpsi to basically ~0psi?
 
thanks for the research Mr. Amish. There's always something to learn !
 
apwatson50 said:
Wouldn't the fuel decrease in temperature. Since it is expanding through a nozzle from ~26kpsi to basically ~0psi?
Click to expand...


No, your thinking evaporation stage in say an air conditioning system. In hydraulics, that same pressure drop through a regulator or orifice with out doing useful work creates heat.

Now take that already hot fuel from pressurizing it, then relief it through a orifice nets you some super hot fuel.
 
Joesixpack said:
No, your thinking evaporation stage in say an air conditioning system. In hydraulics, that same pressure drop through a regulator or orifice with out doing useful work creates heat.

Now take that already hot fuel from pressurizing it, then relief it through a orifice nets you some super hot fuel.
Click to expand...


yep, constant enthalpy pressure drop...but I would bet there is a smidgeon of that fuel that does change phase, but not enough to cool it. However, the heat needed to anneal a spring is real hot...like 900-1200F...would wager the spring is not the issue...most likely the seat gets cut

I see this all the time in steam systems where a steam drum or superheater safety valve becomes garbage after one "operational test" The seat gets cut so bad that it will never reseat.
 
Possibly stupid question, would heat treating make them more durable?

Edit: In this application and still seal or improve ability to reseal or seat.
 
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I would bet the relief is designed for 2 maybe 3 pops, then it's garbage. Heat treat wont help much...a different material "might" help.

Remember, the CR engines have fuel pressures approaching those of water jet cutters. There are some ceramics that can handle those pressures (the jet nozzles), but they will not handle the shock of a chattering relief.
 
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