Navtec Hydraulic Cylinder Troubleshooting Help

[Pyxis156]

I have a split backstay with a Navtec hydraulic cylinder on each of the two legs of the split. I have noticed that lately the backstay has not been centered and upon measuring, sure enough the stbd cylinder is 1-1.5" longer than the port cylinder after pumping to my normal backstay tension.

I tried releasing all pressure to extend the cylinders completely and then cranking them down again but same problem, the port cylinder shortens faster than the stbd cylinder. I read the manual and it indicated that the cylinders utilize an air-pressure return that can be checked and pressurized through a schrader valve at the base of the cylinder. Thinking that uneven pressures might be the issue, I screwed a pump onto the valve to check to see if the pressures were equal and before I could get it completely threaded on the stbd cylinder, very foamy hydraulic fluid came out.

Is this indicative of a leak in the seal between the hydraulic and air chambers of the cylinder? I am assuming this is a bad sign... is a rebuild in my future?

Any input appreciated!

[model 10]

Make sure you re-seal both

[Pyxis156]

Originally Posted by Guy

Make sure you re-seal both

Thanks Guy, I will do both...

[nuku34]

Hello OP:
I've had exactly the same problem with my Navtec split backstay system!
My cylinders are #12 (5/8" rod size, 2" cylinder OD).
If the piston seal is leaking, then oil will get behind the piston into the area that you pressurize with air via the Schrader valve and will come out mixed with air when you push open the Schrader valve.


I'm checking now to see if the piston seal is a proprietary Navtec item or just a standard piston seal available from a good seal/bearing shop here in NZ. Would you know that?


After I rebuild the cylinder, I will pressurize the air side with 100 psi of pressure, but Its still unclear to me if this is done with the piston fully down (pressurized with oil) or up (no oil pressure). Do you know?

[nuku34]

An update on my post of 23 Dec 2023 re my internally leaking Navtec backstay cylinder:
I contacted the local NZ Navtec dealer. They quoted me NZ$360 for 3 seals (piston, wiper and rod) + NZ$100 for international shipping from USA (they didn't have the seals in stock). To rebuild the cylinder another NZ$300-$400! The person I talked to was apologetic about the cost of the seals, but justified it by the usual "original manufacturer parts are better, safer, and more reliable."
This may be the case when dealing with a vang cylinder which has 700psi nitrogen and is complex internally, but the backstay cylinder is simple with only 100psi air in the empty side to facilitate quick return.
I contacted a local (Nelson NZ) hydraulic repair company. The person who did the repair happened to be familiar with Navtec gear, but any competent person could have done the job. Thanks to a kind person on this forum, I had a copy of the Navtec repair manual. The generic seals cost NZ$47, and labour NZ$120. The cylinder is now working perfectly.

It turns out that the piston seal had disintegrated with age (last replaced 20 years ago) and possibly also because a pervious owner had topped up the system with ATF instead of hydraulic oil (ATF eats normal rubber seals).

Happy ending.