Mystery steam engine

[Richard Hed]

Hi Charles, yes, I understand regular twins use a 90 degree crank - and can self-start with no problem. But the local club's compound twin model I had and ran was a 180 degree crank and did not self-start if the pistons were at the end of stroke, as a result. It also had a large flywheel. It was a model made by Apprentices during the 1930s, and was a model of a real engine from early 20th c. My old photos of this engine are poor at showing the crank configuration, but having steamed it more than a few dozen times it didn't self-start when pistons were at the end of stroke. I always set the HP around half stroke for self-starting...
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Not exactly clear in this image...
The 180 degree crank had the HP cylinder directly feeding the LP cylinder through a central valve section of the single cylinder casting, quite like this model. Hence my remarks based on experience of that model. I understood that was necessary where a common steam chest was used as the exhaust chamber of the HP cylinder and Steam chest for the inlet to the other cylinder? - unless a separate intermediate steam store was utilised e.g. large bore transfer pipework? The Stuart Turner Compound twin certainly had a large steam transfer pipe, and a 90 degree crank.
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I realise I am often wrong, but have not seen a clear view of the crank of this engine. (Post 65 picture shows darkness, which doesn't show me conclusively what the crank is like. One big-end is hidden by the support strut. Needs better eyes than mine). Probably missed something in the posts? So I defer to those that know better. Sorry if I am wrong. I didn't mean to mislead.
K2

Whoa Nellie, your steam photo clearly shows valves in the center of the engine but the illustrations show the valves on the outside. The OPs engine shows valves on inside as stated by someone above. So do you still have the engine? Do you know what it looks like when the cap is taken off the valves? Looks to me like your engine is very close to the OPs.

 

[Steamchick]

Hi Richard, I can access the engine, but not immediately, as another club member has it in his charge.
But as a generator engine it has a 180 deg crank, not a 90 degree crank.
The illustration drawings were of the Stuart compound twin, based on the simple twin, which was based on 2 singles....
I understood - perhaps wrongly? - that a compound could feed directly from one cylinder to another directly if the valve timing and pistons were timed together (e.g. With the 180 deg crank). But for a 90 deg crank, the timing is too far apart, so interposing pipework, or a steam reservoir, was needed to store steam from the exhaust of one cylinder and open inlet of the next. This steam (reserve) could also have extra heat added to improve power. The Stuart has such pipework (and they should be lagged to conserve heat). Hence the photos I posted.

Sorry for the inadequate explanation before.
K2

 

[Richard Hed]

Hi Richard, I can access the engine, but not immediately, as another club member has it in his charge.
But as a generator engine it has a 180 deg crank, not a 90 degree crank.
The illustration drawings were of the Stuart compound twin, based on the simple twin, which was based on 2 singles....
I understood - perhaps wrongly? - that a compound could feed directly from one cylinder to another directly if the valve timing and pistons were timed together (e.g. With the 180 deg crank). But for a 90 deg crank, the timing is too far apart, so interposing pipework, or a steam reservoir, was needed to store steam from the exhaust of one cylinder and open inlet of the next. This steam (reserve) could also have extra heat added to improve power. The Stuart has such pipework (and they should be lagged to conserve heat). Hence the photos I posted.

Sorry for the inadequate explanation before.
K2

But that is not what I was getting at. Most twins have the valves on the outside, yours has the valves on the inside. The OPs valves are on the inside. I'm wondering if the two are close relatives?

 

[GreenTwin]

The original-poster (OP) engine has a lot of fine details in it that I don't normally see in model engine kits.
Makes me wonder if it was used for a small steam launch or something, otherwise why include all the functional details like pressure relief valves on top the cylinders, etc.

It also would seem the OP engine is pretty old; dating back to the 1920's or before.
Just guessing outloud.
.

 

[Richard Hed]

Ha! I was just wondering what the IDs and throw is. Lookt thru the post and didn't find it. Did I miss it?

 

[Jasonb]

There are a few models that do have pressure relief valves rather than drain cocks. The most popular is the Boulton triple expansion.

The nearest model to this layout that I can think of is the Muncaster that I mentioned earlier which has its valves between the cylinders, piston for HP and Slide for LP

 

[GreenTwin]

The OP engine has the old-school nuts on it.
Extra height nuts, flat on the bottom, rounded on top edge.
Generally don't see the tall nuts on model steam engines these days unless they are deliberately made that way.

If you see an engine with modern form fasteners, then that immediately moves the engine to a certain date/year range as far as when it was manufactured/constructed.
.

 

[Jasonb]

modern ones are usually stamped out

You can still buy the single chamfer fully machined ones, I use them on all my engines in metric now but have used BA in the past and I think Americam Model Engineering has them in small UNC sizes.

 

[GreenTwin]

So I am guessing from the fasteners pre-1930 ?
.

 

[Richard Hed]

You all are great detectives. What y'all point out is so clever, but I would not have noticed lest you pointed it out.

 

[Richard Hed]

There are a few models that do have pressure relief valves rather than drain cocks. The most popular is the Boulton triple expansion.

View attachment 163708

The nearest model to this layout that I can think of is the Muncaster that I mentioned earlier which has its valves between the cylinders, piston for HP and Slide for LP

View attachment 163707

Would that cylinder valve be made from bronze? I understand bronze wears better and that cylinder valves wear out faster than slides. Is it possible to put a rubber gasket type seal in the cylinder valve?

 

[Jasonb]

Most models tend to use Bronze or gun metal for the slide valve.

As room is limited it is more likely to be the type with adjusting nuts at either end than what you see on a lot of models where the "nut" is actually a cross bar in a slot

 

[Richard Hed]

Most models tend to use Bronze or gun metal for the slide valve.

As room is limited it is more likely to be the type with adjusting nuts at either end than what you see on a lot of models where the "nut" is actually a cross bar in a slot

I am familiar with the D slide type, but the cylinder type I only know a bit about.

 

[GreenTwin]

The saying is "D-valves wear in, piston valves wear out".
A D-valve is self-adjusting for wear, since it floats on the valve rod and can move up and down.
The pressure on the back of the D-valve holds it against the valve face, which is good as far as getting a good seal, but bad as far as excessive wear, especially for pressures above about 100 psi.

A D-valve does not like superheated steam, but a piston valve can handle it fine, and since a piston valve is balanced, it can be operated with little force even at high pressures such as 250 psi or higher.
I have seen some Stanley steam car engines recast from D-valve to piston valve, and this saves a lot of wear and tear not only on the valves, but on the entire valvegear.

The cores required for a piston valve are a lot more complex I think than for a D-valve.
The piston valves I have seen on full sized engines have piston rings, and I think one of the problems with piston valves is snagging a ring on the port.

I think piston valves became pretty standard on locomotives at some point late in their evolution.
.

 

[GreenTwin]

They did make balanced D-valves, which relieved most of the pressure off the back of the valve.
Here is a balanced D-valve I made for the a bottle engine design.
Spring loaded, and a ring goes in the slot.
The cap rides against the steam chest cover, and the top of the D has a hole in it to relieve pressure in the cylindrical area.
This is based on one of the old designs, not my design.
.