As some of you know I have built a model steam platform crane. I recently tested it on compressed air and it ran well apart from the cylinders that I made, they where not to powerful and so I have constructed new ones. Having re-tested it now but on steam it seems to lock up and when I checked the cylinders there is a lot of water in them. The exhaust works I know as it shoots out water / oil there too. I have filled the boiler with water below the level plug and the main steam pipe is right at the top, any ideas! .
I used 'O' rings in the cylinders this time and they seem to be OK when run on air. The boiler is fired using fuel blocks.
I am by no means an expert on these matters, but it sounds to me as if you have the steam condensing in the cylinders before it can do any work. You say that you have made new larger cylinders, which will present a larger mass of cold metal for the steam to condense on. Just a thought - try heating the cylinders, with a hair dryer for example and get them really hot before opening the steam valve. If this works I think you will have to consider fitting drain cocks of some description, but with oscillating cylinders I am not sure how best to achieve this. However I am sure that the far more expert members of this group will advise.
Looks a very interesting project, is it your own design?
could it be condensate from the pipework? small diameter pipe has a very large surface area compared to the bore, insulation might help, admittedly it might ruin the great appearance of the crane. the only other thing is has the cylinders warmed up properly, if they haven't then some steam will condense until they do.
Sometimes I think I'm cynical, then I look at the world and see that I'm not as cynical as real life is.
As the others say, it sounds like condensation. I don't know the design and I'm at work where they block downloads of pictures. However, I note the mention of oscillating cylinders. Are they the sort (like Mamod ones) where the cylinder and valve block assembly will lift away from the port face under the control of a spring (or similar). If so, then with the steam on, I'd rotate the flywheel a few times with the cylinder lifted away from the port face. This should allow the water to be cleared from the cylinders. Do that a few times and the system should warm up and you'll be away.
I will post some pic's of the new cylinders later, I will try a few of your suggestions and let you all know how I get on.
Phil .. The design is from Tubal Cains building model steam engines, I think its the second book. I haven't altered the design other than the cylinders to which I couldn't get hold of the original cast's.
The cylinders are double acting and are sealed well and give very good compression, Maybe to good for the thing to work!.
If insulating is the option, what should I use for this task.
G'day Ace. Try reducing the spring pressure holding the cylinders against the block to just enough to stop live steam escaping. Do the pistons cover the steam ports at TDC and/or BDC? If so the pistons may need thinning or the ports modified. Equally the ports may be too small, ideally their diameter should be just less than the spacing between the inlet and exhaust ports on the base. Its a pain how an engine runs sweetly on air and locks up under steam. Regards, Ian
I have reground the port surfaces of both cylinders to their mating faces on the engine standards as there was evidence that they where leaking. My thought now is that the 'o' rings are the cause as they maybe expanding in the cylinders due to the heat. The cylinders were very hot after the trial run and although there was oil present in the cylinders the pistons were stiff to move. I have stripped down the crane and I am now checking all the motion works for errors. The reversing valve leaked a bit and so I am going to see if I can better the design. Its such a great little engine and I am pleased with my work and its detail that its worth the effort to experiment to improve it.
No. 1. Lose the 'O' rings and use graphited packing or, at a pinch, teflon plumbers tape twisted into a string.
No.2 Lag your pipes by wrapping them closely with cotton twine - it will do the job and even 'look' right.
No.3 As steam4ian said, ease the tension on the springs.
Also, rather than trying to work drain cocks in, you could try fitting a valve in the pipework close to the cylinders - blow some steam thru that to get the piping nice and 'ot, close 'er up and away you go.
Post by Shawki Shlemon on Jul 3, 2007 10:14:00 GMT
Hi Ace These may be stupid questions ,have you tried running on air? What are the materials of cylinders an pistons ? ( if cylinders are iron and pistons of brass then it is possible the pistons will seize when hot) . if everything above is correct then I suspect the valves are leaking .I also agree for this type of engine a graphite yarn will be a better seal . Are you getting reasonable dry steam out of the boiler .
I have run it up on air and it ran sweet, a few minor tweaks and it ran great. Then came the steam test and the cylinders (original ones) struggled to run the winch system with any weight on it so I built new ones. These are brass and have 'o' ring seated in the brass piston. I will try yarn when I rebuild it after doing a few alterations as suggested by others.
I have stripped the crane to bits and have started to clean up on a few bits and I have started to strip the cylinders down and have decided to go with the graphite instead of the 'O' rings. This is now my indoors project as its not requiring any use of the big machinery and its something I can fiddle with on a cold and wet night. Have gone with Tel's idea and have decided to add a blow off pipe under the lubricator, again this can be done using the small gas torch and soft solder. More later.
Sorry.. Cold, wet nights.. Aren't we in the middle of summer time in the UK?/ I hope so as I have booked a ticket to come back to the Guildford Rally next weekend.... Or are you putting off this project until the winter?
Its been raining here for so long that I have decided not to build a pond but to just put some stones around the edge of the one thats been created in my back garden from all the rain we have had. ;D Hopefully you will have better weather down in the South when you come. I am glad to say that I will be jetting off to a more dryer and hotter climate soon. Hope you enjoy the show.