Here is a list of all the postings Mark Knight 4 has made in our forums. Click on a thread name to jump to the thread.
|Thread: Lady Jan steam tug|
Got the boiler steamed today and I’m pleased with how it went. The attached video shows the safety valve keeping the boiler pressure at the working pressure of 40psi. The engine operates well on the reverse valve although there is still some leakage through the piston valves. The reverse valve is still performing well with the O rings providing a good seal in the off position. The valve is slightly tight but the servo manages to push it most of the time. Sometimes going from off to the forward position it doesn’t move but going into reverse and then switching to forward it gets there OK. The boiler can keep up with the engine steam consumption at part speed but not at full speed when under no load. Hopefully when the prop is loaded in water, the reduced speed will mean the boiler keeps up at full power.
Next task is to steam it in the bath and see how it performs.
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.
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.
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
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.
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.
I’ve now finished the new piston for the reversing valve. The fit in the cylinder feels decent but there’s still too much leakage between the inlet and exhaust ports in the shutoff position for my liking. I don’t think the adjustable reamer was the ideal tool for producing an accurate round and straight cylinder as it was only cutting along the middle portion of the flutes. I think a fixed reamer of the correct diameter would be better. Anyway next step is to turn a couple of grooves and insert a pair of O rings. I’ve done some experimentation and it looks like about 7 thou of radial nip across the O ring will work without the ports slicing the ring with every pass. It’ll be interesting to see how long these rings last in this application.
Still not looked at the engine piston valves but going by the box of bits left by my Dad it appears these pistons have O rings at either end. I’ll hence take the pistons out and see if these rings have worn.
Edited By Mark Knight 4 on 28/12/2020 22:00:10
I should also mention the process I’m going through with making this piston as there may be something more I can learn. I levelled my Myford lathe in accordance with the manual before I started and managed to get the turned diameter within 0.01mm down the length of the piston. I then turned the piston down such that it was a slight interference with the cylinder bore. The surface finish was very good from the turning but I then got it even better with some 800 grit wet and dry (the lathe was protected with a cover!). The piston was still a tight fit with the cylinder bore so finally I put some molybdenum disulphide on the piston and attempted to lap the interface with the cylinder. I put the lathe on a very slow speed and held the cylinder on the piston and gradually moved it in and out. It is loosening up slowly put still won’t fully go freely down the full length of the cylinder. I read about this method using molybdenum disulphide on a model steam forum but it had mixed opinions. Is there a better way of achieving a free but steam tight fit between piston and cylinder?
Edited By Mark Knight 4 on 26/12/2020 13:43:10
Hi Richard, this snapshot from the YouTube video linked in my above post shows the engine piston valves bubbling on the top of the engine. There is some steam rising from these when the engine runs. However, I think the worst leak is coming from the reversing valve. It’s a piston type valve and when the piston is centralised (shutoff) there is still quite a plume of steam coming out of the exhaust. I think steam is leaking past the piston directly between the inlet and exhaust ports of the valve. If this was sealing correctly, it would stop any steam leaving the boiler. I’ve now re-reamed the bore of the valve and I’m in the process of making a new piston which will hopefully provide a better fit and seal.
Hi Richard, thanks for this, I’ve now downloaded the orange book. I’ll be in touch once I’ve improved the valve leakage situation (and this Covid nonsense allows us to meet).
Finally got all the modifications finished and steamed the boiler. All went well, I adjusted the pressure relief valve to open at the working pressure of 40psi and it always keeps the pressure below 44psi (WP +10%) as required by the green book.
The exhaust now works fine as I’ve taken the pipe up the inside of the funnel to end above the top. This then has no affect on the flame travelling down the boiler flue.
I've added a centrifugal oil separator to the exhaust which works well along with the pipe and valve for emptying it.
I’ve still not attended to the leaking piston valves and also the reverser valve leaks. However the boiler still manages to hold working pressure with the engine running on the bench. Last job is to have a look at these and see if they can be improved. Anyone have any recommendations? Can piston ring seals be installed or do they just rely on very close clearances for good sealing?
Edited By Mark Knight 4 on 25/12/2020 11:16:33
Some progress to report with the steam tug. I spent a very enjoyable and informative morning over with Richard Simpson earlier this week. He inspected the boiler and performed a hydraulic pressure test, which it passed. Before a steam test is conducted, I have a few changes to the exhaust system to make. As reported above the exhaust was exiting into the chimney which caused a blockage and the flame to back-up. Richard stated this was not surprising and suggested the exhaust was taken right to the top of the chimney. Also I need an oil separator in the exhaust line. I’m now in the process of making one to fit in the available space. Once all this is done and plumbed in, I’ll be steaming it to see how it performs. If all ok, it’ll be back to Richard’s for a steam test and hopefully a certificate.
Time for an update. I thought the tug was finished, so I tried it on compressed air to test out the modified water feed system. I had to bleed the water pump first. I did this by applying a vacuum pump to the bypass water pipe. This drew water through the feed pump and bypass valve. I left the transparent vacuum pipe in the bypass loop so that I could see what was flowing if anything. I fitted a new non-return valve from Macc Models so I also wanted to make sure that was sealing correctly.
I then ran the steam engine on compressed air to drive the water pump. Adjusting the bypass valve worked fine with it allowing varying amounts of water down the bypass pipe. There was however a problem with the water pump leaking past the graphite string. I took it off and noticed that the cylinder and thread that holds the gland for compressing the graphite string weren’t coaxial. Also the clearance between the piston and cylinder was about 4 thou. I bored out the thread in the water pump body by mounting it on a bar I machined to be a good fit with the cylinder in order to guarantee concentricity. I then made an interference fit insert which pushed into the counter bore I’d machined in the pump body. This was threaded on the inside for the gland. I then cleaned up the cylinder and collar with an adjustable reamer and made a new piston with less that 1 thou clearance. Packed with fresh graphite string the pump now works fine with no leaks.
I then steamed the boiler which highlighted a few more problems. First when the engine is running it seems the exhaust chokes off the chimney and forces the burner flame to back-up and not go down the boiler flue. When the engines not running the flame goes straight down the flue. As shown in this picture the 1/4” exhaust pipe goes into the chimney where it turns 90 degrees before ending. I thought this would actually cause a draft up the chimney but seems to cause a blockage, anyone any ideas?
The second problem was steam consumption. Even when the engine wasn’t running the boiler was struggling to get above 20 psi unless I closed the delivery valve off on top of the boiler. It seems the changeover control valve is leaking. I now need to take that apart to see if I can improve it. Also the piston valves on the engine are leaking. Is it normal for these valves to fizz a bit on the top of the engine?
So plenty of work left it seems.
I like a challenge and being a mechanical engineer steam has always fascinated me. I’ll get more pleasure from working on it than sailing it but it would be nice to take my son down to the water as it was originally made for him when he was about 10 years old.
Thanks for the replies, I’ve sent messages to Richard and Stan so I’ll see what they come back with. I’ve read through the notes on the Kirklees club website and I’m a bit concerned that I have no paperwork confirming inspections were passed during the manufacture of the boiler. Does this mean it can never be certified? I’m not sure where I’ll sail it, I don’t have access to a private pond so I really do need to get it certified if possible.
For the non-return valve, I’ve ordered some 5/32” stainless 316 ball bearings so I’ll have a go at cutting a new seat in the housing and getting it to seal.
I’ve now finished the boat. I’ve put a bypass valve between the water supply tube and water tank and rerouted the exhaust straight up the chimney. I turned the brass fittings on my Myford lathe and silver soldered them to the copper pipe. I’ve had it running on compressed air and there are no leaks. I notice the non-return valve on the side of the boiler at the end of the water supply tube does not totally seal. Is this normal? It’s only a steel ball bearing seating on a brass conical surface so I guess it won’t be a 100% seal. I’ve correctly aligned the engine and prop shaft which has made the coupling a lot quieter. Next job is to steam it and see if I can adjust the non-return valve to keep the boiler water at a fairly constant level. I’ve tested the boiler in the middle of the paddock to 140psi and the safety valve blows at 80 psi so I’m happy the boiler is safe.
Ray, I’ve checked the pipe lagging and it is just painted string. This makes sense as my Dad built it from 2005 onwards many years after the dangers of asbestos became well known. I now need to get the boiler certified, does anyone know of someone that could help? I live near Derby but would have no problem travelling if there is no one local.
I’ve now sorted the engine, it starts from any position in both directions at only 10 psi. The problem was the axial setting of one of the valve eccentrics on the crankshaft. It was causing the valve con rod to cross bind With the eccentric when it was at TDC. Once I’d slid the eccentric along the crank to align it with the piston valve the engine runs like a Swiss watch as shown in the new video above. The No 1 cylinder big end bearing has a slight knock so I’ll investigate that further and if shown to have too much clearance, remanufacture it.
Thanks for the advice Ray. I’m still not clear how the water feed bypass valve would work. Is it a valve within a branch pipe between the feed pipe and water tank that would require its opening adjusting by trial and error in order to keep a constant water level or is it a valve that opens at a certain pressure like a safety valve? If it’s the former, I would think the opening to keep a constant level would vary for different boiler pressures and engine power (throttle opening). I don’t think the latter would work because the boiler could still fill at a low enough pressure that wouldn’t open a pressure operated valve.
The water level glass tube is wholly above the flue. I guess it was designed like this so that if the level is anywhere in the glass it’s ok.
I’ve compared the pressure reading on the small Reeves gauge on the boiler with the gauge on my air compressor and both read within 2 psi so no problem there.
Next job is to remount the engine in the boat to accurately align it with the prop-shaft and hopefully stop the coupling from knocking.
Hi Bob, yes at 50 psi the engine self starts in both direction from any position. However below about 30 psi it sometimes sticks and won’t self start. I’d like to improve this because once turning it runs down to only 10 psi without problem. The engine is slightly tight when one of the pistons is at TDC. I’ll probably dismantle the engine in order to investigate. When running on compressed air, I’ve put a few drops of machine oil down the steam delivery pipe and also lubricated all the external moving parts so it isn’t a lack of lubrication.
Edited By Mark Knight 4 on 06/07/2020 10:02:50
Edited By Mark Knight 4 on 06/07/2020 08:50:09
Thanks very much for the replies. I’ve had a look at the Sarik website and they quote 2 boiler sizes, 4” diameter by 11.5” long and 3” diameter by 9” long. Mine measures 4” diameter by 8.5” long so perhaps my Dad customised the length to fit within the space he had available.
I live near Derby so if anyone knows of a nearby club that could help with a pressure test and safety certificate it would be a help. I’m not a complete novice when it comes to model engineering (or full size for that matter). I grew up making steam engines in my Dad’s and Grandad’s workshops and have now inherited the contents of those workshops. I’m also a design engineer by profession with over 30 years working as an aero engine design contractor. The current pandemic has resulted in me having far more time on my hands hence why I’ve turned my attention to this boat which has just been gathering cobwebs for the last 12 years.
With regards to a pressure test, I don’t have access to a hydraulic pressure tester but I air pressure tested it to 100 psi. The boiler was placed in the middle of the paddock so in the very unlikely scenario that it did suffer a catastrophic failure no damage would be done. It passed with no leaks after 30 minutes. This was carried out to put my mind at ease for when I ran the boiler at up to 60 psi on both air and steam. The safety valve didn’t blow at 60 psi and the pressure gauge runs up to 100 psi. Does anyone know what the recommended working pressure is for a Borderer engine running with this boiler? The engine runs sweetly down to only 10 psi before friction dominates.
With regards to the water pump, how would a bypass valve be controlled because the water pump exit pressure would surely only be similar to boiler pressure until the boiler was full of water by which time it would be too late.
Presumably a gas shut off valve would require another radio control channel or is there a passive method for doing this?
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