what gasket material for steam?

[Lopez Mike]

Yes, there needs to be a spring of some sort to seal at very low throttle openings. Once there is significant pressure in the valve chamber this spring does nothing.

If you draw a cross section of that cup and substitute a regular piston ring for the O-ring you will see that the ring is in very much the same situation as when it is on a piston only with the ring sliding on its side. The inside of the cup is at low pressure. The outside is at higher pressure. A tiny bit of steam gets in behind the ring and pushes it up against the valve cover. Those tiny holes under the O-ring shown in the video are probably not needed. The hole communicating between the inside of the cup and the central chamber of the D-valve is needed.

On large balanced valves the ring arrangements got rather complicated with straight segments and adjustable springs and whatnot. A perusal of The Locomotive Cyclopedia is informative.

If I were building this I would, indeed, use a wave spring but it doesn't need to be a stiff one. Again, just enough force to hold the ring against the valve cover at low throttle settings.

[wsmcycle]

I got the 6A back together and ran it on compressed air here in the plant. It runs great astern and ahead. I'll to take it out on the water in the morning for some real testing. (can i make it back to the ramp?) Y'all have taught me much on this crazy steaming adventure.

Thanks

[Lopez Mike]

I just got an email from Stephanie, the owner of Uno and its 6A power plant. She is having a very knowledgeable friend modify her engine as per this cut and paste:
========================
Andrew built new clevises and the redid the bushing in the valve guide. Plus the valve stems are now 3/8 dia.
Quote from Andrew latest email:
" Uno has a really well built engine. except 2 things, in the design. with short engines the valve link angles get extreme so the valve guide does a lot of work. General rule of thumb is the L/D ratio ( length/diameter) of the clevis and guide should be no less than 1 1/2: 1. Uno was .75:1 not good. A little wear and things get out of line quick. The valve stems failed due to the small bending moment at the bottom of the stroke. The other is the builder made the clevises out of leaded material.
So...... We all good now for many, many seasons of running!! "
=========================
Another data point in the search for trouble free operation.

[wsmcycle]

The guide bushings were about 3/4 and the rods were 5/16. I could pretty easily have made the rods 3/8. What are "the clevises"?

[Lopez Mike]

What's on the lower end of those valve rods?

[wsmcycle]

whats on the lower end of those valve rods?

This piece is steel and I agree, It's lowest part would be considered a clevis. The 3/4 dia. is the plunger/piston which slides in the brass guide/cylinder. Which piece was changed and how was it improved?

[Lopez Mike]

Unless I'm mistaken I think that's the feed water pump piston.

The valve rod as stock is 5/16" in diameter and at its upper end goes through a gland into the h.p. valve chamber and through the h.p. valve. Below the packing gland it goes through a guide and then has a clevis that attaches to the center of the Stevenson link. I cannot remember if the clevis is a separate part. Probably so.

The problem as I understand it (always a shaky thing!) is that the side forces below the guide are excessive and cause the 5/16" valve rod to flex and, eventually, break. Going up to 3/8" with all the changes that naturally result from that change, may resolve the problem.

What makes me think that the clevis is a separate part is the machinist's comment that the original builder had made it from Ledloy, a free machining steel. Ledloy has a variety of interesting properties. Most good, some not so good. Non-weldable is important to know. I would be strongly tempted to build any wearing part of the valve gear from hardenable steel, either high carbon or by case hardening the wearing surfaces.

It is most irritating to develop loose valve gear parts. Especially the link as there is no elegant way of taking up wear in the slot. Pins and links can be bushed from the beginning but a slot is an issue. I have remachined them but that has it's limits. I have ready made jigs for small Stuart engines but that is also a pain. Harden the slot surfaces. Period.

The real solution is to make the engine taller with new parts but that seems a bit radical. New rods and round columns isn't too bad but those guide castings would be a puzzle. Don't bring it to me!

[wsmcycle]

The pic is definitely the valve guide. See the 5/16 tapped hole in it? That is for the valve rod. My part was made at .740 and the bore was .758. I ground the .740 diameter down .730 to clean it up then I sleeved and bored the bushing to .732. I only did this on the HP end. That is where my failure occurred. Yes my 5/16 rod broke but something had to give when the linkage bolt came out.

I took her out Saturday and had great success. The engine had never run so well and I was pleased to make it back to the ramp with fire left in her belly. Nothing shook loose because I put jam nuts on all of the linkage bolts

[barts]

Unless I'm mistaken I think that's the feed water pump piston.

What makes me think that the clevis is a separate part is the machinist's comment that the original builder had made it from Ledloy, a free machining steel. Ledloy has a variety of interesting properties. Most good, some not so good. Non-weldable is important to know. I would be strongly tempted to build any wearing part of the valve gear from hardenable steel, either high carbon or by case hardening the wearing surfaces.

It is most irritating to develop loose valve gear parts. Especially the link as there is no elegant way of taking up wear in the slot. Pins and links can be bushed from the beginning but a slot is an issue. I have remachined them but that has it's limits. I have ready made jigs for small Stuart engines but that is also a pain. Harden the slot surfaces. Period.

I've had good luck w/ Stressproof, which is 1144; this is coldworked - 100 ksi yield strength, readily machinable and no heat treat required.. Valve gear bushings can be made from Delrin; this helps keep noise down; pins should be drill rod and hardened. For links on single cylinder engines, I prefer a large disk on either side that is drawn tight by rotating a clamp handle; this stops all relative motion between the link and the link block so long as the link block is a little thinner than the link.

- Bar4t