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Member postings for Mark Knight 4

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
11/09/2020 22:15:56

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.

30/07/2020 10:04:16

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?

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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.

21/07/2020 11:29:54

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.

21/07/2020 09:34:55

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.

20/07/2020 15:56:08

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.

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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.

07/07/2020 08:28:28

**LINK**

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.

06/07/2020 10:02:03

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

06/07/2020 08:47:46
 
Here is a short video of the engine working on compressed air. The engine is timed at 90 degrees, is this correct? As it’s reversible, I guess it will give the best compromise anyway. The engine is slightly tight at TDC for one of the cylinders. At 50 psi, it’s not a problem and will self start in both directions at all positions but dropping the pressure results in it sometimes sticking. Presumably with use it will bed in and loosen up or should I investigate further?

Edited By Mark Knight 4 on 06/07/2020 08:50:09

05/07/2020 22:15:53

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.

There is no condenser tank on the boat, the exhaust was feed from the changeover valve straight into the top of the water tank. There was then a pipe from the tank into the chimney. This just resulted in the water tank pressurising and blowing the water tank lid off. I’ve now changed this to take the water tank out of the exhaust line such that it now goes straight up the chimney. The original arrangement as my Dad left it is shown in this photo along with the lifted lid.

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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?

05/07/2020 08:33:03

A few years ago I inherited this 95% complete steam tug from my father who built it between 2005 and 2008. It is a work of art and engineering. I’ve never found the drawings but I know it is a Mobile Marine Models Lady Jan hull with a Borderer piston valve steam engine made from Reeves castings. Does anyone know who’s design of boiler this is?

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I’ve got the engine and boiler out and working well on compressed air. The coupling to the prop shaft needs attention because the shaft and engine are not aligned so is very noisy.

The boat has a water pump which is geared to the engine. The engine exhaust steam is piped through the water tank but this just pressurises it and blows the lid off. Is this normal practice with a steam plant to recover some of the exhaust water? Also the pump has no control, how do I guarantee it delivers the correct amount of water to the boiler? I’m tempted to disable the pump and just run the boat for a limited time with the water in the boiler.

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Any help would be appreciated with getting this boat going.

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