Experience of A.A. Leak's compounds

[steamboatjack]

The system is just the same for any type of compound, use the dimensions of the L.P. (both if a four crank triple) but using the data as though this cylinder was taking steam at full pressure.

Regarding the Balanced slide valve on the Leek, I am not convinced that the balance would be very useful as per the drawing? I would certainly machine “water grooves” in the face running on the valve chest cover to seal this. The exhaust appears to exit through the cover, this is not always desirable and balanced valves do not need this if its better to exit in the conventional way.
As I understand it the theoretical balance would be calculated as follows. On the valve working side:- the area of the valve x steam pressure less the area of the balance seal x steam pressure, However additional loading is imposed by the balance valve :- the area of the balance disc x steam pressure less the area of the seal x steam pressure.
With a large balance disc needed to allow exhausting through the cover this must be significant.
With an unbalanced valve the exhaust cavity pressure is trying to lift the valve, I have ignored this effect on a balanced valve.
On my own design, the balance disc is smaller as the centre space is communicated to the exhaust cavity by a drilling only, this has the added advantage that should a failure of the balance system occur, the hole can be blocked and the valve run as a conventional type. Below is my design giving about 60% loading based on the above.

[Mike Rometer]

Thanks Jack, it seems almost too simple after the mess I got into. I'm no mathamatician but given an 'example' I can usually work my way through it and come out the end with the right result, but this time I couldn't get the calcs to give a sensible result when I adjusted the ratios of the cylinders. Basically your method just ignores the ratio.

[johngriffiths]

Tenacity's 3+5x3 Leak has run for many hundreds of hours and the only things done to the engine have been to change the solid pump arm links for the marine type with adjustable caps; take up all wear on the marine type cross head bearings until the rods would remain at 45 degrees when swung out and to put a light spring on the delivery valve of the Edwards air pump.

Reg Lindop reduced the feed pump plungers to 1/4" diameter from the 3/8" diameter originally fitted and whilst this was ok on the Bridgewater canal (slow engine speed) this was too small when on Windermere so I refitted the 3/8". I put wick oilers in place of the gravity feed system fitted by Reg because this either flooded or failed. Reg used CI castings for the feed pumps and the seating on the delivery check valves had broken up so I bored them out, threaded and sleeved with phosphor bronze, which were pinned to prevent unscrewing. I also make sure the valve lift was not large to reduce hammer, just over 1/4 of the diameter of the hole is lift enough.

There are problems with the drawings and one which caught out Jon Wade was the crankshaft centre bearing which is shown 1/8" too long. The balanced slide valve almost strangles the exhaust in the chest cover, the link slots need to be 3/16" longer etc.

John Griffiths

PS Reg fitted marine crossheads in place of the launch type when he built the engine in 1986, there was less than 1/1000" ovality on the steels when I did the brasses.

[Dhutch]

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

We also have a narrowboat with a 4.5+7/5*4 Leak engine, build by Anthony Beaver, who also build the engine in narrowboat Tixal which is very similar to our own. Infact of the eight active narrowboats in existance, thats three with a leak compound, and a four with a very simularly proportioned cochran build compound.

Since its installation we have made a number of changes which I list below, many of which have also been made by geoff (tixals engine remains as far as im aware largely as ours was when new), however we are very happy with the performance of the engine. We run the enigne with operating speeds of around 150-250rpm, limited by boiler, upto around 330/350 in short bursts when manovering. Driving a 26*32inch blade, in full gear, on live steam at 150-200psi. Assuming its in plausable working order, the airpump maintains 15-22inchs (circa .6 bar) of vaccume.

Ancillaries include an HP crosshead driven modified (double acting) edwards airpump, LP cross-head driven water circlulating pump, and inboard surface condensor, as provided with the engine, a crank driven three-ram presurer washer pump for boiler feed and a modified coach alternator to provide domestic electical generation.

Main alterations include.
- Removing the engine mounted speed wheel infavour of a remote lever operation, and regulator.
- Remaking the LP piston in alumium to reduce moving mass and reduce balance issues.
- Removing the two piston pumps fitted on the sides of the airpump in favour of the belt driven feed pump.
- Retiming valve gear to give reliable start/stop and better steam cut off, etc.
- Replacing the orignal lubrication system with a machanical displacment type unit, using flexable nylon feeds.

The engine, boiler and boat where commisioned in 1991 and have extensivly cruised the UK canal system in the following 20 years, racking up an estimated 6-8000hours operation.



Daniel

[steamboatjack]

Daniel,

I have just had a run on "whistle down the wind" which also has a large Leak engine, A very nice setup.
I now have the drawings to hand as I am planning to make one next (if I live that long) It looks basically a good design but there are a few things I will change. The most obvious is that the crankshaft diameter is too small at 1.25” I would use 1.5, like wise the cross-head pin arrangement is poor an too small.
The "british disease” of too short connecting rods is also here, at least another inch here would improve the valve geometry.
I would use marine double bar links as the wearing surfaces are much greater. I will start a re-design in the winter so if anyone wants a new engine 15-20 IHP?
Regards
Jack

[malcolmd]

Just to say - "thanks for all the advice" - the engine is progressing well, and while the drawings/description are proving to require a little "interpretation" the build is going well so far, having erected the main castings... see http://sy-befur.co.uk for progress http://sy-befur.co.uk

[Dhutch]

I have just had a run on "whistle down the wind" which also has a large Leak engine, A very nice setup.

Delay in reply, but glad you enjoyed, I have also been out on wdtw, I assume 'steam geoff' is Mr Laycock and is refering to wdtw no less.

Daniel

[Dhutch]

there do not seem to be a lot of these around (about 5 in the SteamBoat Association's register)

I make it around 11 and current count.