A Marine Condensing Engine

Would a compound self start if the HP was at approx TDC or BDC as there would be no steam to the LP which would have it's crank in the right position unless a simpling valve were used in which case it's not really "self" starting

I'm not sure it would Jason but it definitely wouldn't if the cranks were at 180 so you are potentially right it would not be 'self starting' but near enough - save that one position

Isn't a simpling valve something that would be fitted as standard on a compound/ triple? One is not shown on this drawing but could easily be so

It's certainly something the compound traction engines have both full size and model so you can send a bit of high pressure steam to the LP valve to get things moving so could be worth adding to yours.

For a compound steam engine, does the angle between the cranks have a significant effect on how well the engine runs? I.e. is there an optimum angle where the exhaust valve for the HP cylinder and the inlet valve for the LP cylinder work together and give more power than a more random timing?

Or am I over-thinking this?

Dave

From what I can see in the limited references on marine engines I have there is no reference to cranks at 180 degrees. All engravings and images show them to be at 90 degrees so I can only assume that is the convention.

The previous comment on direction of rotation is still an open one - which cylinder leads the other for instance - again I assume it's the HP to LP in forward motion but don't actually know - I will keep looking for some indication that that has relevance but not able to find anything so far.

Tug

As they are double acting I don't think direction will make much difference unlike an IC engine.

Pg 455 MacGibbon's Marine Engine Knowledge

Ahead rotation is clockwise with a RH propeller

Tug & Jason: thank you for your replies (regarding the angle between the cranks). There is also the relatively large pipe joining the HP cylinder to the LP cylinder which will help, too. My mind has been put at rest!

In my own defence, I had just been watching a video of Ilmor’s 5-stroke IC engine, where the phasing of the exhaust from HP to inlet of LP cylinders is critical.

Dave

Buried deep in my shed I have a MacGibbons, or the bible as it was known back in the mists of time when i was doing my tickets. All forgotten now, too long ago. Must check it out seeing as we are now back into the old steam stuff!!

Lets assume the ship has a RH prop then and do the crankshaft accordingly, HP leading the LP seems the most logical.

So good that an innocent question can provoke so much discussion and then an answer - great stuff these forums!

Chris

Clockwise or antiCW will depend on which end of the shaft you choose to look at. CW looking from astern seems to be normal for single screw vessels, twin screw ideally should have a handed pair.

90 degrees is good since it means that your simpling valve will actually work to help start the engine. It doesn't matter which ones leads since they are usually double acting. So either the top or bottom LP inlet will open when either the top or bottom of the HP is about half way through its stroke.

There is a convention on locomotives for which side leads. If anyone tells them your model is wrong tell them they are looking too close.

There are at least two different types of simpling valve. The most common is probably the shot of steam type, which just feeds a bit of inlet steam direct to the receiver, putting back pressure on the HP. A more sophisticated type uses more valves and reconnects things so that both cylinders take boiler pressure steam in and exhaust to the LP exhaust side. This gives more starting torque, at the expense of heavy steam consumption, and is more likely to be found on a locomotive than a marine plant. Some old timers called the simpling valve the "God Almighty".

My own plant will reverse most of the time just by throwing the lever over, but has the shot of steam type of valve for that one time when the wharf is rushing up, you throw over the lever, and nothing happens. Actually it is more likely to fail to reverse in that sort of situation, since you are probably already throttled back to very low inlet pressure to go slow, whereas if you are cruising along at a good speed and throw it into reverse, there is plenty of pressure and the water forces on the prop are likely to move it off dead centre too. So the usual practice is to throw the links over and give it a little shot as well, before you even know if it has decided to reverse. It has an American locomotive style Johnson Bar rather than a more typical marine style screw reverser, since a small boat is more likely to need to reverse frequently than large boats do.

John

Morning guys, more good stuff, thanks as always

10Ba - I pondered over which way to look at this at first but came to the conclusion this would be looking at it from astern - a RH prop would be turning clockwise which John (Olsen) now confirms. That is how I will do with this model then with the HP leading the LP in that direction.

Simpling valve - I am aware of what it is for and when it would be used but no other knowlege. I've never fitted one to a model so far. I was under the impression however that this allowed steam (air on this model) at inlet pressure to be diverted direct into either cylinder. John mentions 'the reciever' so now a bit unsure how this is set up.

That brings me to another question - Nearing the end of the main cylinder parts I realised that the engine as designed has no drain valves. Easy enough to deal with that by fitting the usual side bosses for take off but it lead me to thinking where do marine engine drain points actually drain to. Is it to atmosphere somwhere external to the engine room or into a collector or indeed to the condenser itself. Some full size 'marine' knowlege would be helpful here for sure so if anyone can comment further on the last two points it would be appreciated.

Began machining the parts for the piston valve block yesterday - all going well and no further mishaps. I'll make sure there are pics of the relevant parts before the JBW goes into action

Regards - Tug

Edited By Ramon Wilson on 26/02/2021 08:15:48

Ramon. it shows two drain tappings on the underside of the cylinder block as well as one on the HP inlet

Some engines actually have some volume between the HP exhaust and the LP inlet, most don't, so receiver is just a fancy or maybe short way of saying "the piece of pipe between the Hp exhaust and the LP inlet". Of course sometimes this is actually built into the castings so there is no external pipe at all. My simpling valve just takes steam from the main steam pipe to a tapping on the said pipe. It would probably be nicer to take the steam from after the throttle valve.

My drain cocks just vent to atmosphere. Probably not ideal, it would be nice to save the water. Into the hot well would be my choice, you don't want the vacuum plumbing too complex as leaks in it are hard to trace.

Unless you are modelling a specific full size prototype, you don't have to worry too much about being strictly correct to full size practice as most possible variations will have been tried somewhere. So as long as it is reasonable and works it is ok

John

Thanks Jason and John

Yes I had noticed the HP inlet drain and having had a fresh look found the two lower drains on the passageways. Doesn't show anything on the GA or for the top of the cylinders though - easily done however.

John - Understood on the 'receiver' - I'lI look into this further. I can see the logic of not providing areas for potential leaks but on an engine in an engine room the drain must have gone to somewhere specific. Although this is not a scale model per se I would like to make it and it's features as fair to the full size as I can if possible so though this does not have to be 100% it would be nice to follow full size where possible. It's more important (to me) that it's there in more or less the correct manner than it's potential working effectiveness.

We have close by where I live the 'Lydia Eva' the last remaining steam powered Drifter. It has a triple I believe so may be worth a visit once restrictions lift. That said I do know one of the curators - all I need is to find how to contact him.

Sun's shining, garden's calling - I'll give the black stuff a rest - well for the morning at least

Regards - Ramon (Tug)

Hi Tug, Have you got a copy of Ronald H Clarkes "steam engine builders of Norolk " There are many diagrams Etc in it. There were a supprising number of marine engine builder in the county. Noel.

Hi Noel,

Thanks for the suggestion but no, I don't have a copy and it's a very long time since I saw one - early model engineering and 'library sourced' days I think. What memory I do have of it was that it was mainly traction engine builders so was surprised by your comment.

Late this afternoon I suddenly remembered I had a quite old telephone directory hidden away. Had a look and there was a listing for my old friend Morris who is the curator mentioned previously. Gave it a ring and caught up with him. Obviously the Lydia Eva drifter is affected by lockdown restraints but he assures me the cylinder drain valves simply vent in the 'sump' below the engine and then down into the bilge which is pumped out at regular intervals and removed when the engine is running. As he remarked though, in its former working days that would have been straight over the side! Incidentally Morris was the guy interviewed by Neil Oliver when the vessel featured on the BBC's Coast program.

I guess there's no need to be any different then so I'll run the pipes 'below'

Tug

Morning guys, I've just had a call from my friend Morris. Apparently after we spoke he and the engineer felt they should take a socially distanced check just to make sure everything was all okay on the boat.

Morris took the opportunity to have a check where those drains actually end up. So the info, as from the horses mouth and hot off the press, is that the HP and IP top and lower drains come together as four pipes and disappear into the sump as said but the two on the LP cylinder are conected directly to the condenser.

As he describes it the exhaust from the LP takes the form of a cast extension of the (horizontal) cylindrical condenser and the two pipes are plumbed directly into that. In the interests of following a full size practice I think I will do the same via a spacer between the exhaust pipe and condenser flanges or similar.

Back soon with some pics

Tug

Hi Guys - on the home run as far as the cylinder head is concerned - all the major parts done but still seventeen small bits left to do

Here's the piston valve chamber parts. Slip jointed similar to the condenser the groove is to get a definite JBW seal around the ports. The ports were filled with slices of compressed polystyrene foam packing to prevent the JB from ingressing the ports. Once bonded, that was simply disolved out using a dribble of cellulose thinner in each port.

The bonded valve chamber along with the other parts. The discs are the infil into the bottom of the cylinders - the original drawing has bores closed at the bottom.

At this moment the piston valve chamber is being bonded to the HP cylinder, just the spacer between the two cylinders to do before it can be put together but I'll wait until all those smaller pieces are done before bonding it all together.

It is progressing though, despite that garden distraction - Tug

Nice work Tug - just a quickie, what clearance do you give in the slip joints that are then filled with JBW? And are the cylinder bores just fine turned to diameter or did you hone them as well?

Chris

Hi Chris

It's not measured as such but 2-3 thou I guess. JB has great gap filling properties but ideally it needs to be a loose but not a rattle fit - if too tight then the JB gets forced out. The action of bringing them together seems to self centre the parts, but the idea is to leave a small amount of material on to clean up anyway if required.

The cylinder bores as such are off the tool. I did get a hone out in anticipation but the finish in both bores turned out very good if I say so myself - certainly better than anticipated but I may still run the hone through before the assembly for as said the bores are blind and once in place honing will not be possible.

Regards - Tug