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Lady Jan steam tug

Does anyone know the design of this boiler?

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Richard Simpson28/12/2020 22:26:18
1027 forum posts
256 photos

You might be lucky Mark and just need to replace the 'O' rings. That's a lovely job on the reversing valve by the way.

Actually an adjustable reamer should be a better tool for the bore as a fixed diameter reamer has to cut as it is presented into the bore. An expanding reamer can be completely inserted into the bore before it is expanded slowly to give a cut the full length of the bore. Hopefully you will get the ends sealed with the 'O' rings but there is always going to be a little internal passing as a result of the clearance fit.

Mark Knight 429/12/2020 16:24:52
21 forum posts
15 photos

Thanks Richard, finally SUCCESS! I turned a couple of grooves into the reversing valve piston, installed a pair of O rings and sure enough no leakage in the shutoff position. It’ll be interesting to see how long the O rings last as it isn’t ideal that they pass over the port holes every time the valve is operated. This also causes some resistance although it appears the servo has sufficient force to overcome it fortunately.


I took one of the piston valves off the engine and it doesn’t have any piston rings. My Dad must have experimented with the O rings as in his box of bits was a piston with O rings as shown below with the one off the engine. It has been run in the engine as I can see the wear marks. Perhaps he found the additional friction was a bigger problem than a bit of steam leakage.


By far the worst leakage was through the reversing valve which I’ve now sorted so I’m going to leave the piston valves as they are. All the recent running has been done on air for convenience so I just need to steam it for a final check and then it’ll be finally finished.

Richard Simpson29/12/2020 17:00:22
1027 forum posts
256 photos

Mark, Getting some steam oil around the valves might be all they need to reduce the leakage to a level you are happy with.

Richard Simpson29/12/2020 17:01:14
1027 forum posts
256 photos

Hopefully your 'O' rings will survive but going past a sharp edged port usually seems to damage the surface.  You can only try.


Edited By Richard Simpson on 29/12/2020 17:03:17

Mark Knight 430/12/2020 09:46:00
21 forum posts
15 photos

In an effort to prevent O ring damage, I’m going to try and break the sharp edge where the port holes meet the cylinder surface. Easier said than done on a 5/8” diameter cylinder with 1/8” diameter ports. Only way I can think of doing it is to make a tool that back faces the surface through the port. A 1/8” drill with the flutes ground down except for near the tip should do it. Any other ideas would be welcome.

Mark Knight 409/01/2021 14:29:57
21 forum posts
15 photos

I’ve now designed and made a back facing tool for chamfering the corners between the port holes and cylinder wall that the O rings pass across. The head is made from silver steel which I quenched and tempered for a decent compromise between hardness and toughness. It has worked well and removed the phosphor bronze cylinder corner just by careful turning by hand. The operation of the valve as the O rings pass the ports now feels smoother so hopefully the rings will remain steam tight for longer.



Edited By Mark Knight 4 on 09/01/2021 14:41:10

Ray Wood 209/01/2021 15:41:07
2847 forum posts
993 photos

Hi Mark,

With your piston valves such small diameter it's difficult to pack them with graffited string as a normal piston would be in the engine, "O" rings are commonly used for sealing round a piston rod with good effect in lieu of a packed gland.

As the "O" ring is slightly compressed it will be tempted to be cut by port openings ? Full size loco piston valves are fitted with rings to make the seal.

Slide valve engines are so much easier

Regards Raytrojan 1.jpg

Mark Knight 409/01/2021 18:11:50
21 forum posts
15 photos

Hi Ray,

Yes, I don’t think viton O rings would last long sealing the piston valves. For that reason I’ll accept the slight leakage. There was a much worse leakage through the reverse valve. I’ve solved that with O rings as I think they will last far longer in there compared to piston valves due to only seeing 10s of cycles per hour of running rather than 10s of thousands.

I can see why my Dad built the piston valve version of the engine even though there are problems to overcome. It is a far simpler installation in a radio controlled boat. There is only one radio channel required for full control of the engine and no complex reversing linkage that you need for slide valves.

Just got to put it all back together now and give it a final steam test.

Richard Simpson09/01/2021 22:31:14
1027 forum posts
256 photos

Lovely job on the back facing tool Mark. I'm sure that only a slight chamfer will be needed to prevent damage of the 'O' rings. As you rightly say the operation of the reversing valve is minimal compared to the piston valves so treating them differently sounds like a sensible approach. Looking forward to you telling us it is working OK!

Mark Knight 410/01/2021 10:11:10
21 forum posts
15 photos

Thanks Richard, the encouragement is much appreciated at these times of isolation! I’ll update once I’ve steamed it and hopefully get to visit you sometime later this year.

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