1802 Bell Crank Engine

[Jasonb]

Thats OK, I thought the temptation of a Governor may have been too much for you, good to see you are resisting.

Some quite nice drawings here

[philjoe5]

Since the Bell crank design was patented in 1802 and I believe the James Coombes Table engine came later I assume Coombes took that vertical crosshead guide arrangement and connected it straight to a journal - crankpin.  Both engines were designed to give a small footprint.  I wonder which design was favored at the time?? 

Cheers,
Phil

[Dave Otto]

Interesting project Jo,

What purpose to the tails serve?

Dave

[Jo]

Hi Phil, The later table engines designs are head and shoulders above this early engine:

This Bell Crank engine is a condensing engine and is fitted with Murdock's long "D" slide valve which is driven by the eccentric on the crankshaft (side of the flywheel) Ports with flat faces were cast at each end of the cylinder keeping the steam passages in and out of the cylinder as short as possible. The D valve stretches between the ports for the whole length of the cylinder and is flat on the side next to the ports and semi circular on its back. The exhaust passage was cast into the whole length of the valve to carry the steam away to the condenser.

As a result the engines had poor thermodynamics because the exhaust steam inside the valve passage was being heated by the incoming fresh steam. And the other problem was keeping the packing round the semi circular back tight 

Dave: I thought I had a drawing somewhere of those tails being used to drive the paddles on a stern wheeler but I currently can't find it.

Jo

P.S. In case anyone did not know William Murdock with Mathew Murray were Boulton & Watt's "chief engineers". Murray's short valves were a much better design 

[Dan Rowe]

Hi Jo, Murdock invented the slide valve which was the long form. I have been very interested in this form of valve because the very early Shay locomotives used a long slide valve but it was called the double D valve on a Shay because it had two separate valves but it is still essentially the same as the long slide valve.

Dan

Edit Murdock's slide valve is British Patent number 2340 of the year 1799.

[Jo]

Hi Dan, yes what you are talking about is the modification that came in for the improving the Murdock valves:

The middle section of the valve was replaced by a rod or rods joining the two ends, the result was a much lighter weight valve. It also had the advantage that it was no longer necessary to plane the entire length of the valve chest the only two areas needing planning were under the faces themselves. They were still a devil to get to seal 

Jo

[Jo]

  These castings are all over the place, The base is under height on one end, over on the other. It is too wide but if I mill both sides down to get the right width the sides will be about 1mm thick and as it is gunmetal it will end up a bit soft

Did I mention anything about the square nuts and bolts? Well if you are making one of these then please don't follow the article which says you need 80 pairs and whoever originally had this engine had kitted themselves up to make all of these. But for the life of me I can't find anything like that number. There are a number of what I think should be studs that could have been square bolts on the original but I am not sure that there is the clearance for the heads to turn (unless they are clearance holes) and you know how much I like my studs 

The material that has been supplied is BMS but I do like stainless fasteners on my engines these days... do I really want to start milling round stainless into square to make the fasteners 

Jo

[Jasonb]

As its gunmetal why not slice it down the middle and solder back together and add a bit of height where required at the same time. I did at one time quite fancys making one of these without castings, the base casting is only a box with a few attachments so easy enough to fabricate.

As we said the other day I think its nearer a total of 80 fasteners not 80 each of nuts and bolts

[Jasonb]

Back to casting sizes again, on the height have you allowed for the thickness of the brass beading that needs to be added to the lower section?

Also are you using the 1.875" width or the width over the beading of 1.937" when you say its too wide?

[Johnb]

A nice old engine. I'm looking forward to following the build. I remember the later one in the Science Museum. A good looking engine.

[smfr]

Good to see you back on steam, Jo  I will follow along with interest.

Simon

[Captain Jerry]

This will be an interesting engine build to follow.  Lots of detail and a different geometry.  The cam ring and follower are a real departure from the usual eccentric. The castings and the Anthony Mount model show a round cam ring and I cannot see any benefit to a "squashed" one as shown on the patent engraving. I would bet that the patent engraving is a distortion by the engraver and not as actually designed.  the long D valve will also be a challenge, I would think.

Jerry

[Alan Haisley]

This looks like another to learn a lot from. 

Alan

[Jack B]

Hi Jo: I read all the postings on your engine. I am going to follow along and wish you the best of luck. I think it will involved some interesting machining.  Jack

[fumopuc]

Hi Jo, I like the kinematics of this engine. Good to see you starting an other steam engine build again.