YH first disassembly - did I find a problem?

[JimD]

I noticed a small leak at the top of the high pressure cylinder and decided it was time to do a limited disassembly of that area of my YH. I've had it for about a year and a half and have 8-10 hours on it, I think. It would still fill my 45 minute SCBA tank to 4000 but seemed to be doing it a little slower than it used to. I think I found the leak at the fitting for the steel line coming out of the top (and could have just tightened it) but I also noticed something that doesn't look right to me on the gasket at the bottom of the high pressure cylinder I'd like your input on.

I will attach a picture of the high pressure piston and the gasket. I think the piston looked good with just a small amount of black slightly oily residue that was easily wiped off. The reed valves were clean, no residue on them at all. I use Nuvair 751 lubricant. My concern with the gasket is that it is over the reed valve. I would think the valve should be on top of the gasket. Is this correct or normal? If not, where can I get a new gasket. I put it back together as is and it seems to be working fine.

 

[chrisbee]

Jim, I believe the way you found it is correct; the reed valve placed under the gasket.

The reason I say this is the reed valve must lie flat and close as possible to the cylinder surface to effect a seal.

If the gasket is put in first then the reed valve on top of it, the gasket will cause a gap between the cylinder surface and the reed valve thereby not allowing the reed valve to seal. Pressure would not build in the low side because the reed valve would allow bleed back due to the gap caused by gasket.

In other words, the reed valve must seal against the half moon indentation in the cylinder surface that you see on the opposite side of mounting pins of the reed valve. If the gasket is under the reed valve, that would create a gap and the reed valve would not be able to create a seal in that half moon indentation as it flexes.

I hope that makes sense.

 

[Gerry52]

It PROBABLY leaked from the dowty seal (bonded washer) at the top of the high pressure cylinder. They're known to do that. If you'd just replace that seal your YH might have run for another year or two w/o problems. BUT, now that you've opened it up, you should probably do an R&R on it. The reed valve & gasket are where they should be. There are a bunch of vids on YouTube about rebuilding & doing it correctly. MAKE SURE you don't flip over the reed valve when you put it back on! Use a slight amount of sealant on the gasket.

 

[Long_Gun_Dallas]

I'm not aware of any dowty seals, and I've torn mine down a lot. Though my memory may be betraying me. Usually it's just a fitting or compression seal that is leaking. I've used valve lapping compound to get the compression seals to seat better, or to stop leaking after disassembling, and actually found it necessary to do so in some cases as they just would not hold a seal anymore. I've never replaced any compression seals, just take the fitting, put a tiny bit of lapping compound on the seal, press the fitting againt the seal, and rotate it a bit back and forth with some pressure on it (just using my hand/arm to apply pressure against the mating surfaces) rotate back and forth to create a bit better of a seal. Lapping compound is meant to make a better seal for valves on a cylinder head and the principle is very similar to what I'm describing. Clean compound off since it is an abbrassive then reassemble.

 

[JimD]

I saw something I did not understand at the top of the high pressure cylinder but I just left it alone. I reassembled it and tested it and, after I tightened the fitting on top of the high pressure cylinder where the tube attaches, it is working well. I guess that is the dowty seal but it does not seem to be leaking there.

Thanks for the explanation of why the gasket is installed over the reed valve. That makes sense. Didn't look right to me but it makes sense now.

I expect to have to rebuild my YH but I will wait to do it when it isn't working well. That may mean I have to dig out the manual pumps at some point but I can live with that until I get it rebuilt (or another one purchased).

I was encouraged by the lack of signs of wear and minimal carbon buildup. I think my expensive oil may be helping.

Thanks for all the helpful thoughts.

 

[JimD]

I refilled my 45 minute SCBA tank from about 3200 psi up to about 300 bar today. I put three frozen diet Dr. Pepper bottles in the coolant bucket and ran the YH for about 17 minutes. That is faster than I was getting before I took it apart a little and reassembled. I would typically stop at 4000 psi after about 20 minutes. With the ice in the coolant, a lower ambient temperature here now, and my normal radiator on the coolant my temperature only got to about 53.3 degrees C. I am happy with the way it is running at the moment. Thanks again for the explanation on the gasket.

 

[bckyrdsnpr52]

I noticed a small leak at the top of the high pressure cylinder and decided it was time to do a limited disassembly of that area of my YH. I've had it for about a year and a half and have 8-10 hours on it, I think. It would still fill my 45 minute SCBA tank to 4000 but seemed to be doing it a little slower than it used to. I think I found the leak at the fitting for the steel line coming out of the top (and could have just tightened it) but I also noticed something that doesn't look right to me on the gasket at the bottom of the high pressure cylinder I'd like your input on.

I will attach a picture of the high pressure piston and the gasket. I think the piston looked good with just a small amount of black slightly oily residue that was easily wiped off. The reed valves were clean, no residue on them at all. I use Nuvair 751 lubricant. My concern with the gasket is that it is over the reed valve. I would think the valve should be on top of the gasket. Is this correct or normal? If not, where can I get a new gasket. I put it back together as is and it seems to be working fine.

View attachment 297345

View attachment 297346

Keep an eye on those 2 tiny pins, they come out easily and easy to lose!

 

[bckyrdsnpr52]

I saw something I did not understand at the top of the high pressure cylinder but I just left it alone. I reassembled it and tested it and, after I tightened the fitting on top of the high pressure cylinder where the tube attaches, it is working well. I guess that is the dowty seal but it does not seem to be leaking there.

Thanks for the explanation of why the gasket is installed over the reed valve. That makes sense. Didn't look right to me but it makes sense now.

I expect to have to rebuild my YH but I will wait to do it when it isn't working well. That may mean I have to dig out the manual pumps at some point but I can live with that until I get it rebuilt (or another one purchased).

I was encouraged by the lack of signs of wear and minimal carbon buildup. I think my expensive oil may be helping.

Thanks for all the helpful thoughts.

I would go ahead and order a couple of the second stage pistons. That usually will fix lower than normal pressure issues as long as you dont have a leak. It takes a couple of weeks from aliexpress