Experience of A.A. Leak's compounds

[malcolmd]

He explains me the option he proposed to convince your Ministry of Finance , we will be very happy to see you and show you our boats and workshop, and Paris and/or Versailles where I live:)

Hello Thierry
Yes I think the opportunity to come and see you and the boats and workshops in Paris or Versailles is very attractive one! My wife teaches at school , so I think we will need to schedule this in the school holidays - assuming that Bruno has managed to find/count the castings!

Malcolm

[malcolmd]

Hi Mal, Gearing could be applied either way...if you had a long stroke low speed engine and a hull with a small clearance for the prop. you could gear the speed up to allow a smaller propellor. <snip>

The boiler I am building is a three drum Yarrow style of thing, an 8 inch steam drum and two 5 inch mud drums. Five inches is too small for easy expansion of the tubes, they should have been at least six, <snip>

Incidently I did make one major modification to the Leak, I fitted a piston valve to the LP as well as the HP. <snip>

Interesting John - I had always thought (not being nautically knowlagable) that running props very fast was not efficient (cavitation and all that), so I had assumed that there would be an "optimum speed"...

On the "expanding the tubes" I was also thinking that expanding the tubes in the SBA's design with 4 inch mud drums almost 30 inches long might be something of a "challange" ! - I am assuming you can get "round the corner, long-handled expandery thingies"....

Twin piston valves.... I think I will stick with the balanced slide valve, as that should avoid the loading problem, but I must confess that as I am still just tooking at the drawings in the Cambden "guide" (as opposed to the real drawings) it is hard to quite see how "balanced" it is!

[Mjolnir]

There might be an optimum size for propellors, but I suspect that it is bigger than anything we can normally fit in. So for practical purposes, use the biggest diameter you can reasonably fit in. If that is quite big, then use narrow blades rather than the wide ones seen on infernal combustion engines, eg use a typical "steam wheel".

I expanded my tubes with some tube expanders purchased from India, They are of excellent quality and do the job well. But to work inside the mud drums, I had to shorten the taper and the body of the expander back. To drive them I used a setup that would have made Heath Robinson proud, a pair of bicycle sprockets mounted on a long steel bar that would pass right through the drum. One sprocket is on the end, the other about the middle. The middle one has a square in it to drive the expander and the end has a stub that is driven by the battery electric drill. It works fine although I would not say that the whole thing was great fun. I actually have four expanders, since the spec for the boiler allows more than one type of tube, and I ended up with two different wall thicknesses. So I have two expanders for each size of tube. Each expander only expands up to a certain size.

I think the balanced valve should be fine, it must be balancing about 80 to 90 % of the area. I was just being different for the sake of it, and since I was making my own patterns there was no reason to stick rigidly to the design. Incidently with piston valves you really must have good drains and releif valves.

regards
John

[malcolmd]

There might be an optimum size for propellors, but I suspect that it is bigger than anything we can normally fit in. So for practical purposes, use the biggest diameter you can reasonably fit in. If that is quite big, then use narrow blades rather than the wide ones seen on infernal combustion engines, eg use a typical "steam wheel".

I expanded my tubes with some tube expanders purchased from India, They are of excellent quality and do the job well. But to work inside the mud drums, I had to shorten the taper and the body of the expander back. To drive them I used a setup that would have made Heath Robinson proud, a pair of bicycle sprockets mounted on a long steel bar that would pass right through the drum. One sprocket is on the end, the other about the middle. The middle one has a square in it to drive the expander and the end has a stub that is driven by the battery electric drill. It works fine although I would not say that the whole thing was great fun. I actually have four expanders, since the spec for the boiler allows more than one type of tube, and I ended up with two different wall thicknesses. So I have two expanders for each size of tube. Each expander only expands up to a certain size.

I think the balanced valve should be fine, it must be balancing about 80 to 90 % of the area. I was just being different for the sake of it, and since I was making my own patterns there was no reason to stick rigidly to the design. Incidently with piston valves you really must have good drains and releif valves.

regards
John

That's really helpful, do you have a web link for the expander supplier ? - and the HeathRobinsonness sounds fabulous...

On the drains/relief front I cam across a really nice design (in Model Engineer) that I (nearly) put on the steam loco... they were a small piston valve, that was held closed by boiler pressure, so when used as drains you just shut the steam supply off and cylynder pressure opened them, and when the supply was restored and closed them any excessive pressure would overcome the boiler pressure and force them open. It seemed like a really neat design and avoided lots of linkages to open them all at once...

[steamgeoff]

hi i run a 5x7.5x4 leek in a 57 foot narrow boat it goes very well give me a ring if you want any more info tel 07971204594

[Mjolnir]

The expanders I used came from :
http://www.powermaster.in/
They were no problem to deal with and sent things promptly. They don't do credit cards so you have you jack up a bank transfer.

The drain valves you mention are exactly the sort of thing I have put on mine. mine have an o ring for the seal in the operating cylinder and they work fine...they act as a releif valve as well as a drain cock since if there is enough pressure in the cylinder it will force the valve open against the steam pressure. (I have put on conventional relef valves as well, but there is nothing like being sure.)

There are bigger versions of the Leak engine, that one should be a good match for a narrow boat that size.

regards
John

[steamboatjack]

Expanders are available in the UK see www.wicksteed.com
Regards
Jack

[malcolmd]

Expanders are available in the UK see http://www.wicksteed.com
Regards
Jack

thanks Jack!

[malcolmd]

The expanders I used came from :
http://www.powermaster.in/
They were no problem to deal with and sent things promptly. They don't do credit cards so you have you jack up a bank transfer.
John

Thanks John

[Mike Rometer]

Regarding the power of a compound, the best rule of thumb is what was known as "referred IHP" simply ignore the HP and calculate the IHP of the L.P. as though it was a single cylinder engine but operating at the full available boiler pressure using the time honored PLAN/33000 formula. With the mean effective pressure taken at 60% of the boiler pressure you get a fair idea of the power.
at 120PSI boiler pressure and 450 RPM we get 9.6 IHP. (72PSI MEP)
To get 11.2 you would need a MEP of 84PSI rather high for 120PSI supply. I am sure there are none that run at 450RPM anyway.

Regards
Jack

Being still a "looker" (I can't help it if I'm beautiful ) not yet a doer, I'm intregued by this 'rule of thumb' for calculating IHP of twin compounds, but what do you do for triples (or more)? A little while ago I did try to calculate the power of a small triple and got in a fearful mess.