Notes on Drawings and Design
While in my opinion the Leak Compound is the best marine compound design on the market, it seems to be quite well known that there are a number of errors (and omissions) from the drawings for the Leak Compound. As a service to the community, I am publishing the errors I have found in the drawings and would welcome input from others as to any “quirks” they have found.
In the process I have also developed a reduction drive for the pumps (to allow the engine to rev faster) and a step-up drive for an alternator to provide power for burners, navigation lights and radio – creating the drawings for this have taught me not to be too critical of others mistakes – it’s hard … :-)
Having “finished” and tested my engine there were a final set of issues that I suggest you keep an eye on:
Piston Rod Lubrication Fitting Clash: The drawings show the small-end and cross head lubrication is achieved via drillings at the top of the piston rods. There is no indication of how oil is delivered to these drillings. I have arranged this using small-bore flexible nylon tube and push fittings. I installed a small elbow into the feed hole to allow the push fittings to point between the bores. However, space is very limited here, being close under the lower cylinder covers and stuffing box glands. When I packed the glands I found that as these sat slightly lower they clashed with the oil feeds at TDC. I can see no way to move the oil feeds. So I resorted to machining away some of the bolting flange of the stuffing-box glands next to the columns. This has worked, but clearances here are tight.
Air Pump Drain Modification: the drawings show a simple drain plug screwed into the bottom of the air pump body. In my design of pump drives this is hard to reach, and having a circulating pump exhausting into the condenser, you can get into the situation where the condenser becomes full of condensate if the main engine/air pump is not running. So I have brought this drain out to a simple taper cock. This just makes things a bit easier.
Pinning the Drop Arms: During early testing I found the drop arms had a tendency to slip on the weighshaft. So I installed small taper pins to secure them.
Reversing Lever Clash: This was just me not spotting a problem earlier. I fitted the weighshaft at the top of the column position. On final installation I discovered the level collides with the exhaust pipe in full-ahead. Just keep an eye open. 🙂
An experiment – Steam Operated Combined Drains & Relief
Much earlier in the process I baulked at drilling the cylinder castings for the cylinder drain cocks because they looked hard to drill with out risking damage to some rather expensive castings. Moreover, previous experience with manual cylinder drain cocks on the loco had been poor (leaky, difficult linkages etc.) and on the steam launch most people seem to opt for 4 manually operated cocks which involves a deal of “faffing” in use. Continue reading →
So, following some communication with the steam boating forum we are all agreed that the Edwards Air Pump as drawn is missing anything to hold the valve-plate in place, or seal its contact with the pump body. This means that:
The whole valve tends to move up and down with the piston rod, (and I think this needs to be a “good” fit to prevent leaking round the pump-rod, so this is unavoidable).
There is nothing to seal the lower valve plate (the one with the holes) where it sits on the ledge of the pump body…
So, my solution is to:
fit a gasket under the valve plate
make and fit a nylon block to hold the plate down – made 10 thou too long, so that the top cover provides some “squishing pressure”
As other members suggested this may help pump performance by removing “deadspace” (but it is beyond the valves so I am not sure if this is correct), and secondly it needed to be made in a way that ensured the outlet port is not cut-off if the block rotates; so, as can be seen in the pics below, I have made it with an exhaust annulus and internal ports to the valve chamber cut in the bottom…
I think this approach will also prevent the valve opening too far….. a test in the kitchen sink proves that it all works!
Here are some pics of the block and completed pump assembly.
I think there is a problem with the air pump design/drawings…
This looks like it’s not a problem with the drawings, so much as an oversight in the design…
The outlet flap valve assembly is not fixed/located by anything vertically within the outlet chamber… neither is the lower valve plate – part 3 on P20 of the book – (the one with the holes) sealed against the lip it rests on above the cylinder….so (as I noticed when I completed a trial assembly) the whole valve (both plates and the rubber washer) move up and down with the piston rod, and even if the vacuum held it down, I feel sure any hard won pressure difference would be lost as the air leaked back into the pump round and under the valve plate.
My current plan is to make a nylon “block” which is a light push fit in the outlet chamber, has “ports” to let the air-water out to the delivery port, and is slightly longer than the available space, so that when the top cover is fitted it will press the lower valve plate down onto a gasket I am fitting under the valve plate….
does anyone have any better ideas/opinions? am I missing something?