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 →
For about a year now I have been saying “Yes, the engine is done, apart from a few bits and bobs” – so the other week I found myself waiting for some timber to arrive and decided to just “knock those bits and bobs on the head” – 10 minutes inspecting the engine revealed that there were in fact (at least) 23 jobs still to be done!!! So so far we have spent two weeks reducing this list to 7…. (and deciding to do some much later!) Herewith some notes on some of this activity… 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?
I have puzzled over the drawings of the Impulse Valve for a year or more, and spoken to others who can make no sense of it.
Well finally last week while mulling the design over with a friend, he (I think) correctly fathomed how it is meant to be built and operate…
As drawn there appears to be a plunger in a tube which is operated by a press button. There appears to be no way that this would operate, as it would just admit HP steam to the chamber formed between this plunger and the end of the valve body….
The explanation is that this plunger is in fact a tube! Thus when depressed the steam is admitted to the end of the valve assembly, and then passes down the tube to the valve chest/cylinder. There are hints in the drawing that this is the game, but some of the views are incorrectly drawn which leads to the confusion – and actually I am not even sure it could be reliably constructed as drawn.
I think it would still be hard to make this valve steam tight, but in operation this might not be a practical problem…. Thanks to Neil Davis for figuring this out!
*Simpling or Impulse
In the ME words, Mr. Leak complains that many people incorrectly describe the Impulse Valve as a “Simpling Valve”, and he argues that this is wrong as it does not make the engine run as a simple (which is true) but just introduces a HP steam feed into the LP valve chamber to push the engine off HP TDC if it stops there.
He’s right in the description of what it does, but knowledgeable friends of mine tell me that within the road steam community (Traction Engines) these valves on compounds are always known as “Simpling Valves”… so maybe we can continue to use the term…
There is a clash in the drawings between the bolts holding the reversing lever slider pivot (shown in the scrap drawing on page 33 of “the book” entitled “Reversing Arrangements”, and numbered item “2”) and the upper-right stud securing the LP Chest to the LP Cylinder….
Having hit the problem, I moved the pivot in-board about a quarter to miss – I now have an ugly hole to plug 😦
Also take care, I think the original hole locations in the pivot are also incorrect, as they seem to result in the slotted arm (item 3 in above drawing) fouling the studs on the LP valve cover. So I made mine (the 2nd one!) a bit longer and located holes by eye.