Pallnet Fuel Rail leaks

[SleeperZ]

I am extremely frustrated with the 1/2" threads on my fuel rail. I was originally using a brass reducer bushing to adapt my 3/8"NPT fittings to the rail. I think the rail threads are cut too deeply, as I nearly bottomed the bushing (hex head) into the rail using 2 layers of yellow teflon tape. It was quite tight, I may have applied 30-40 ft-lbs, as much as I dared, and this thing still leaks.

 

I switched out the bushing for a 1/2" brass pipe nipple (no hex head to bottom out), and cranked that down as tight as I could, and it still friggin' LEAKS!

 

What's next, JB Weld? I've been plumbing biodiesel processors for years and yellow teflon is the best stuff I have found. Yes, way better than liquid thread sealants.

[z240]

I'm wondering if the rail isn't cracked. Inspect it carefully.

 

What size fuel rail are you running that uses a 1/2" NPT inlet! and better yet, what massive fuel sucker motor are you feeding with it?

 

The repair will likely involve welding up the hole and/or crack, drill and re-tap.

[NewZed]

Have you communicated with Pallnet? A simple courtesy. He might have reports from others if there was a mistake.

Edited June 21, 2012 by NewZed

[kaito]

Hey sleeperz, pallnet actually recommends using jb weld to install his fittings for the barbed rail. I just used some form-a-gasket (fuel resistant one) and that fixed te leak I had.

[SleeperZ]

Have you communicated with Pallnet? A simple courtesy. He might have reports from others if there was a mistake.

Only reason I have not is I bought it from a third party, not directly from him.

[SleeperZ]

Hey sleeperz, pallnet actually recommends using jb weld to install his fittings for the barbed rail. I just used some form-a-gasket (fuel resistant one) and that fixed te leak I had.

That is encouraging. I don't have much to lose at this point, except if the rail is damaged it will make it harder to repair. I doubt it is cracked though, I would think the torque I am applying to the threads would split it, and not hold like it does.

[SleeperZ]

I'm wondering if the rail isn't cracked. Inspect it carefully.

 

What size fuel rail are you running that uses a 1/2" NPT inlet! and better yet, what massive fuel sucker motor are you feeding with it?

 

The repair will likely involve welding up the hole and/or crack, drill and re-tap.

Yeah, 1/2" NPT is large. It's the standard 11mm O-ring rail, it's basically threaded to the ID of the extrusion, much larger than the 3/8" (6 AN)I originally plumbed from my fuel filter and regulator.

[dexter72]

I second the JB Weld Fix, I made my own rail a few years ago and use jb-weld on the threads. No leaks in 5 years.

[Noddle]

I used this on my Pallnet rail

 

Permatex High Performance Thread Sealant - 50mL

 

no issues todate..

 

Nigel

 

[Tony D]

ARGH!

Sealing NPT Threads is a simple job since the advent of Loctite PST!I had to do a big training session with our assembly group in Shanghai, many argued the points, but when assembled as taught, our leak rate went to nothing!Summing it up:

1) Teflon Tape is an anti-gall compound, over tightening is possible with it, it just doesn't work well as a sealant and it's downside outweighs it's perceived advantages. Use of Teflon tape is forbidden on any connection in the oil system on our equipment.2) Joint must be CLEAN-alcohol is a good residue-remover and final cleaning solvent.3) Apply primer if available, to male and female threads.4) Apply Loctite 567 PST to male threads, make sure it goes to the ROOT of the male threads.5) Turn in fitting finger tight, then 1.5 to 2 turns more MAXIMUM (540-720 degrees of rotation). Smaller fittings may not be able to be turned this far, the smaller the fitting the less past finger-tight you will be able to turn it, 1/4 NPT may only get 180 Degrees before "tight"!6) When possible, let the fittings cure two hours before pressurizing. On smaller fittings and lower pressures seal may be affected immediately, but it will get stronger with time.7) If the fitting is in the wrong position and you move it after more than one or two minutes, remove, clean, and reapply sealant as cure has begun and disturbing it can introduce a leak-path.8) OVERTIGHTENING CAUSES GALLING OF THREADS AND LEAKS!9) Proper threads cut will be sufficiently tight to affect a seal at 720 degrees from finger tight WITHOUT SEALANT. If the fitting turns in further, one of the threads is improperly sized or worn from over use, overtightening, or being made in China.10) Proper threads, with Loctite PST 567 applied and screwed in FINGER TIGHT and being allowed to cure have been found without leaks in helium service at 10bar! Overtightening is a major cause of leaks due to deformation of threads (they DO MAKE NPT HELICOILS!) -- leave it slightly loose and let the sealant do its job!

My classroom demonstrator is a manifold of several 3/4NPT fittings, one of which is LEFT FINGER TIGHT. By the end of the demonstration I apply pressure and check with Snoop. As much as people shake their heads and argue about it in the class, the final demonstration shows that finger tight fitting holding at 10bar!

My guess is the JB-Weld solution is a compensation for poor field practices. It's a bonding agent more than sealant. I'd defer to Loctite PST over JB Weld simply because you can take it apart later for whatever reason. Loctite Green (cylindrical parts locker 608, or wicking 270) also works well, but the PST works really well.

[Tony D]

Noddle's Permatex is a PST Variant. Each has specific qualities for operating temperatures and pressures but my bet is that it will solve the issue same as PST567.

[Tony D]

One other note: TORQUE is not a valid measurement of NPT Joint Makeup for many reasons. The accepted standard is anywhere from 1.5-3 turns from finger tight, depending on size.In the size range we are discussing I doubt you will get more than 1 full turn on it.

You will notice the turns spec will compensate for threads wearing--if you bottom out before making a specified turn... It's oversized ir the fitting is undersized. You either need a helicoil, or properly sized fitting (some come severely undersized!)

[SleeperZ]

I certainly appreciate the technical explanations. Aside from my ignorance of over-tightening NPT threads, I started with normal assembly techniques, and only increased the torque after my original installation leaked from the get-go. And it's only one end.

[Tony D]

Don't feel bad. When I did the examples the guys at our factory STILL didn't believe me. The next day I saw four guys with a 36" Stillson and a 2M snipe on it reefing in a 2" pipe to the body of our Main Oil Pump (no, that wouldn't POSSIBLY distort the pump body would it?) they were going for 'another turn' rather than letting it "loose" and allowing the sealant to do it's job!

 

I felt a lot better after we contacted the Loctite Rep, who was 'local' in that he was the same ethnicity. When he did his demonstration and barely turned a 2" fitting 360 degrees from finger-tight there was palpable discontent. As a few field guys interrogated him, he stood firm and insisted that was enough. A roar went up through the crowd. Nobody could believe a fitting "so loose" could hold ANY pressure. I couldn't speak the language, but by body language alone I know this was the case. So quickly I grabbed a regulator and screwed it into another fitting on the base plate and started pumping air into the vessel.

 

Less than 15 minutes from turning in the fitting, the big fitting held 5psi (this was a hot oil reservoir that never saw more than 1psi if that...)

 

It's very common, the educational level about proper bolting and threaded connections out there is amazing. When YOU start getting blamed for leaks (and nobody else in the world has them...) you start looking closer and learning a LOT about how to correctly put fittings together!

 

When I started in Hydraulics, it was ALL metal-on-metal sealing. You learned CLEANLINESS was #1, wrapping of the dreaded teflon tape properly was #2. When those first Anerobic Sealants came out widely, it was like a GODSEND! Suddenly fitting makeup was EASY! But that lead to shortcuts, and nobody trained 'the old ways'... There really is no substitute for the basics: a clean joint, and proper fitting makeup and tightening. You do that, and you will have a good leak-free joint. Once you master that technique, sealants only add a margin of insurance, and the ability to make up the joint with far less angular motion. Meaning it comes apart and goes back together easier when it's maintenance time.

 

Hope you got the leak nailed. If the fitting is bottoming out, you can helicoil the NPT, use red loctite on the outside of the coil going into the fuel rail, and PST 567 on the Male Threads of your fuel fitting after giving the red some time to set up properly. You should then be able to remove and remake the fitting without worrying about pulling the coil out later on.

 

But if it ain't leaking...no need to take it apart again, right!

[aarang]

The 1/2 inch NPT threads were double cut on my Pallnet rail. It leaked no matter what I tried including the 567 PST. The JB weld method was suggested to me, but I was not comfortable with that solution. I ended up welding some npt reducers into the rail. No leaks since then.

[cockerstar]

Does the rail have welded mounts on it?

1/2 NPT sounds like one of the rails I have made, as I haven't heard of any others with a large bore like them.

 

When I tapped the threads on them I used the 1/2 NPT to -6AN fittings I was shipping a lot of the rails with as a gauge for thread depth. Some of the cheaper fittings I picked up at home depot would seat pretty far in, but all of the rails still held 80PSIG of air pressure for several minutes.

 

I haven't had any reports of a leaky rail make it back to me, but I'd be happy to provide whatever help I can with the rail.

 

Starting with clean threads is an absolute must, and Tony's advice on using the proper sealant is spot on. I did ship all of the rails that came with the AN fittings with the yellow teflon tape you've been using. LocTite PST is a better solution, and that's where I would start after inspecting for thread galling. Making sure that the rail isn't cracked would also be good, but I doubt that "30-40 ft/lbs" would cause that kind of damage.

[letitsnow]

My rail from pallnet had the threads cut just a bit deep, the earls fitting nearly bottomed, but I got it to seal so I never brought it up.

[SleeperZ]

No, the mounts are not welded. I got zero time on the car this weekend. I am going to hit the parts stores this week, and pick up a good sealant as well as a new cap and rotor for my other issue.

[cockerstar]

If the mounts aren't welded, then it isn't one that I produced. Starting with some LocTite is a good direction to go, regardless of who made it.

Hopefully you get it all sorted out (both issues)! Keep us posted

Edited June 25, 2012 by cockerstar

[Tony D]

" Making sure that the rail isn't cracked would also be good, but I doubt that "30-40 ft/lbs" would cause that kind of damage."

I would disagree! ESPECIALLY if it was lubed with teflon tape. TORQUE is the resistance to rotary motion read on your wrench. On a common fastener, 15% of that resistance is friction on threads, 75% under-head friction, and 10% stretch on the fastener providing clamping. Changing the thread or underhead frictional coefficient can radically overtension the stud leading to breakage. Something small like changing from a graphite based to Moly-Based thread lube can affect the tension by as much as 300%!

On NPT threads, just about the ONLY thing you have to resist torque IS thread friction! And this is compounded by the wedge action of the thread formation. Putting teflon tape in there radically changes the makeup torque---especially as the torque rises, and the teflon gets a chance to extrude and let the threads 'slip'!

Proper thread makeup is starting with a clean dry fitting and determining depth at finger tight (which is somewhat subjective, but reasonably controlled) and then to go anywhere from 1/2 to 2 turns more with the fitting.

Thread condition (burnishing) and thread sealant used can RADICALLY change how far that thread will engage--and subsequently which 'wedge loading' you will have from the taper.

There is a reason everybody is saying 'check the rail for cracks'! It's SO common that the threads are 'torqued' instead of 'turned in' that the fittings on alloy parts split!

Put an inch-pound torque wrench on a 1/4npt fitting and screw it in using '1 turn from finger tight' DRY and watch what happens as you 'torque monitor' that fitting on the first, fifth, and 10th installation. Each of those would produce a leak-free seal on clean-dry threads (or should!)

From that demonstration alone you will see the torque variance rules out torque as a valid way to measure if it's 'tight enough'.

Now put teflon tape on a new fitting, and with a new hole, turn the threaded fastener in to the same series of torques you recorded on the first hole. By about #5 I'm betting your thread is 100% bottomed in the hole---even though it was 'tapped tight' and had an issue fitting to proper depth initially!

Like I said, I have a demonstrator for this stuff doing Training in China. Thread sealants and anti-friction anti-gall devices work great IF you use the proper installation method.

I would venture to guess that 30-40 ft-lbs on a teflon taped 1/2" NPT fitting is about 100 to 200% overtorqued! Meaning colossal overstresses and thread deformation occurs in the female threads.

They make up and stay leak-free with incredibly low torques... In the long and short of it, the NPT fitting is really an 'ANGLE-TURN' fastener, like many engineered fasteners on cars today. It's just the education about that point is lacking.