Lex Teredo

Navtec Backstay Cylinder Question

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I recently had a NavTec AP 250 piston re-built with new seals, bench tested, etc.  When I reinstalled it on my J/35, I had a lot of leaking from the hydraulic male JIC fitting on the cylinder, where the hydraulic line (female) screws onto the JIC fitting. 

To stop the leak I plan on putting a couple wraps of plumber's tape on the threads and re-installing the hose a bit tighter, but I also noticed that there wasn't a rubber O-ring or crush ring inside the female fitting on the hose. 

I'm familiar with Is there supposed to be some kind of seal on the female fitting?  It looks flared rather than an O-ring fitting.  But if it doesn't have a seal, how much ought the female end be tightened? 

Because it's oily, and a threaded 7/16ths fitting, I fear stripping the threads.  My intent is to tighten the fitting, then pressurize the -10 system until it leaks, snug it up another half turn, pressurize it again, and so on until the leaks stop completely up to around 4500 psi, which is about 25% over normal "high" operating pressure.  Is there a better way?

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The seal is between the 'cone' around the hole of the male fitting and the identical 'cone' inside the female fitting. Teflon tape will not solve the problem. Disassemble, check the mating surfaces for clean, no scratches, etc. Re- assemble & tighten more.

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Flare saver if there is even the smallest scratch on either fitting face to stop leaks. I believe navtec fittings are JIC -6 maybe-8

 

seal-installation.jpg

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If it's a dash -10 cylinder it will be a -6 (3/16) hose fitting.

if the swivel nut on the hose fitting is tight there won't be any play between the swivel nut and the rest of the hose fitting.

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The JIC fitting on the elbow and the hose end has a 37degree flare on it, and it should not have been changed when the service work was done; they are made from stainless and are very reliable. 

Teflon tape on the threads won't solve the problem - the flares have to match us. Perhaps you could try ordering a JIC plug from McMaster Carr - https://www.mcmaster.com/#50715k522/=1cm4hkb

and use that to see if the end fitting on the hose is leaking. If not the hose, then the elbow should be replaced, which does get installed with teflon pipe tape. on the pipe threads. 

Bam Miller 

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Bam is being easy here, NO tape on the JIC fitting. It will most likely interfere with the mating surfaces causing leakage and could add the benefit of getting into the oil, then the pump, etc. which is potentially bad.

Plugging the hose and pressurizing the system is spot on. I would add that a place to look is between the elbow and the cylinder body. Between the stainless elbow and the aluminum female thread with some anger I have seen the elbow win a few times. You mentioned it was bench tested so this is not a high probability. 

You can lighten up on your tightening procedure. With no pressure in the system you should be able to tighten the hose onto your cylinder with average strength on an 8" cresent and see no leaking. If you do then something is amiss. 

In general with hydraulics, clean the living daylights out of everything then do your testing. If it's not spotless it is very hard to see where the issue is.

Thanks.

Mark

 

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It's all good now.  I wiped down the fittings, then tightened it up a quarter turn at a time and tested with a little pressure each time until I turned it one last quarter turn and it felt like the nut came to a "stop" - light to moderate effort wouldn't turn it any further.  And that's when the leak stopped. The system is working fine, no leaks.   Thanks all for the tips.

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