Author Topic: Four Valve Non-Releasing Steam Engine  (Read 89299 times)

Offline Captain Jerry

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Four Valve Non-Releasing Steam Engine
« on: September 02, 2012, 04:06:25 AM »
Last month I started talking about designing and building a Corlisss type steam engine and started a discussion in the "Twenty Questions" section with the hope of getting some input from forum members.  As you might expect, I got lots of good information and suggestions so I am ready to start this new project.  Thanks to all of those who contributed to the pool of information.

I started thinking about building a model steam engine based on the Corliss  Valve design but as I got a little further into the design, I realized that there are problems that cannot be resolved if I try to build a true, working, Corliss style valve mechanism to be powered by compressed air.  S0....I am going to build a model of a later design that is often confused with the Corliss mechanism, (at least by me).  The value of the Corliss design is the sharp steam cut-off at variable crank angles, under governor control. By closing the steam valve early in the cycle, the steam expansion is used more efficiently, and by varying the angle of cut-off, the power can be matched to the load to maintain a set speed.  The Corliss design changes the steam cut-off angle without  affecting the exhaust valve setting.  The most recognizable feature of the design is the ?wrist plate? on the side of the cylinder and the four radial rods that operate the four valves.
The ?Four Valve, Non-Releasing ? engine  is based on a valve design that appears quite similar to the Corliss valve and overcomes some of the shortcomings of the Corliss design.  It uses a similar cylinder form and the four valves are operated with rods radiating from a wrist plate.  BUT it does not incorporate the ?quick drop cut-off? of the Corliss design.  In its simplest form, power and speed are managed by a throttle valve under governor control.  In its most complicated form, it uses two eccentrics and two wrist plates.  One of the eccentrics and the associated wrist plate controls the exhaust valves and the other eccentric and wrist plate controls the steam valves.  The steam eccentric uses a governor to advance the eccentric angle, much like an automotive distributor uses manifold pressure to advance or retard the spark.
The shortcomings of the Corliss design that this engine overcomes are:
 
      • Initial cost
      • Maximum speed
      • Later cut-off
Initial cost is obviously higher with all of the additional parts required for the Corliss quick cut-off mechanism. The maximum speed of a true Corliss engine is also limited by the reaction time of the dashpots and return springs to between 100 and 150 RPM.  Later designs increased the maximum speed to 200 RPM.  This is fine for mill operation where  belt and shaft transmission control the final shaft speed but it is too slow for some other applications such as electric power generation.
The most important shortcoming, from the viewpoint of this model, which will operate on compressed air is that the Corliss quick cut-off cannot be configured to occur much later than about 50% of piston travel.  Compressed air does have a small component of expansion but not that much.  Early cut-off just does not work with compressed air.

This is obviously an oversimplified description of these two designs and if you want to get deeper into the subject with a more qualified source, you should read Audels Engineers and Mechanics Guide 2 available here:
http://books.google.com/books?id=5_pYAAAAYAAJ&printsec=frontcover&dq=editions:pi7LBdCfU5wC&hl=en&sa=X&ei=3uERUKXAKajF6wGDn4HoAg&ved=0CDgQ6AEwAjgK#v=onepage&q&f=false
Thanks to Arnold for this link.

This is what my design looks like at this point. 



I am using Alibre' 2011 for all 3D modeling and 2D drawings.  The details of the design may change as the build progresses but I will
try to post updated details as they occur.

I actually got some work done today.  I started with the cylinder because it offers the most new challenges. The first thing is to get the stock to size.  The finished size if the cylinder block is 2" long by 1.5" high and 1.25 wide.  I used my table saw to get the stock to rough oversize:



And then brought it square and to dimension with a flycutter. I then used my edge finder to locate the center of the face to drill for the wrist plate pivot and the four valve bores.





The valve bores are .25" diameter finished.  I located them from the center point and and then drilled 3/16", 7/32" and 1/4".  I know from previous use that this 1/4" bit produces undersized holes which will be reamed to size in a later step.  The last operation in this setup is to return to the center and drill a flatbottomed hole with a 1/4" end mill for use as a locator for the wrist plate pivot.



The next step is to bore the 5/8" cylinder bore, centered in the end face.  I do not have a lot of confidence in ability of the X2 mill column and dovetail slide to stay vertical for this operation.  The bore is 2" deep and there is enough flex in the column to give problems, even with a boring head so I decided to do this job in the lathe.



That is a piece of 2" square aluminum tube bolted to the lathe cross slide.  The cylinder block is bolted to the square tube with shims to bring it up to height.  It was set parallel to the lathe ways using a dial test indicator swept against the far edge.



The part was centered horizontally using a center finder to locate frond and back faces and the dimension divided by two, just as you would do on a mill table.  Sorry, I forgot to photograph this operation.

The hole was pierced with a 3/16" drill bit and the progressively opened with 1/4", 5/16", 3/8", 1/2" and 5/8" drill bits.  For each of these operations, the tailstock feed was used to  drive the part into the drill bit to avoid any off center forces that would cause the part to lift or twist. 



The final passes of the 5/8" bit were driven by the carriage feed lead screw with the bit rotating at 2000 RPM and well lubricated.  The end is as good as or better than I have ever been able to achieve with a boring bar.  Honing with abrasive will be done later.

The final job before leaving the shop for the day was to put a tapered top face and spigot on the top plate and to mill a rebate on the edges for hold down bolts.





It is late and I have l small glass of Jack Daniels with an Ice cube trying to get my attention.

Jerry



« Last Edit: September 04, 2012, 01:40:12 AM by Captain Jerry »
NOTARY SOJAK

There are things that you can do and some things you can't do. Don't worry about it. try it anyway.

Online steamer

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Re: four Valve Non-Releasing Steam Engine
« Reply #1 on: September 02, 2012, 04:12:38 AM »
That's a flying Start Capt!

Dave
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Offline zeeprogrammer

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Re: four Valve Non-Releasing Steam Engine
« Reply #2 on: September 02, 2012, 04:42:05 AM »
Wow, what a start!
That's going to be a good looking engine.
Carl (aka Zee) Will sometimes respond to 'hey' but never 'hey you'.
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Offline Dean W

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Re: four Valve Non-Releasing Steam Engine
« Reply #3 on: September 02, 2012, 04:51:38 AM »
What the other guys said;  A great start.  This should be an interesting engine to watch running.  Lots going on.
Dean
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Offline swilliams

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Re: four Valve Non-Releasing Steam Engine
« Reply #4 on: September 02, 2012, 07:17:15 AM »
I agree; this looks like it will be very interesting

Steve

Offline NickG

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Re: four Valve Non-Releasing Steam Engine
« Reply #5 on: September 02, 2012, 08:27:29 AM »
Haven't had a chance to read properly how it works yet Jerry - have a feeling I'm going to get shouted at any minute for coming straight on the forum 1st thing in the morning!

The design looks very elegant though and interesting. Great start, I'll definitely be watching this.

Nick

Offline sbwhart

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Re: four Valve Non-Releasing Steam Engine
« Reply #6 on: September 02, 2012, 09:37:35 AM »
I've got my chair pulled up to watch this one Jerry great start of an interesting design.

Stew
A little bit of clearance never got in the way

Offline Don1966

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Re: four Valve Non-Releasing Steam Engine
« Reply #7 on: September 02, 2012, 02:07:00 PM »
Hey, I want to ride along on this one too. Looks like a great project to learn on.

Don

Offline Bearcar1

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Re: four Valve Non-Releasing Steam Engine
« Reply #8 on: September 02, 2012, 03:26:26 PM »
Having thoroughly enjoyed the results of the many unique engines you a have done up in the past, I am definitely looking forward to seeing this one come to life as well, Jerry. I've always held a curious fascination with the Corliss design and just barely understand the valve mechanism but they are a real thing of beauty to watch in motion. Slow and elegant are two descriptors that come to mind.  :ThumbsUp:


BC1
Jim

Offline Captain Jerry

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Re: four Valve Non-Releasing Steam Engine
« Reply #9 on: September 03, 2012, 02:15:51 AM »
Thanks for watching.  I think this is going to be a fun engine to build.

It is unusual enough but is still pretty mainstream.  Most of the components are common to other steam engines so not really all that difficult.  The cylinder block is one of the recognizable features.  Rectangular and massive.  I had always thought that they were solid hunks of metal but I should have known better.  That rectangular shape is sheet iron or plate cladding, enclosing a large amount of dense insulation material, designed to keep the cylinder hot but also to isolate it from the exhaust manifold which is cooler. 

At the present scale, I'm going to treat it as a solid block but it would be possible to fabricate a more authentic core for someone with a foundry or to solder brass rod or tube together and cover it as in full size practice.

Yesterday, I got the cylinder and the valve bores located and drilled.  Todays big job is to mill the steam and exhaust passages and drill the passages from the valve bore to the cylinder.

In this picture, the cylinder block is set up in the mill vice and the edge finder is touched to the front and back faces to locate the longitudinal axis.  Two steel shafts are inserted in the valve bores and located with the edge finder to get to the center of the top face, where the X and Y readouts are zeroed.  I find it much easier to work from a center reference than from an edge when working with a symetrical layout.  All offsets are identical left/right and fore/aft with just a +/- sign change.



I used a 1/4" end mill to mill a longitudinal slot from one valve bore to the other.  I had set the depth by touching the end of the cutter to the top of one of the rods and setting a depth stop on the mill column.  The slot is milled from the midline of one valve to the midline of the other.  I took three passes, increasing the depth until I hit the preset stop.  I then milled a cross slot at each end after increasing the depth of cut by .125" so that it bisects the valve bore.



The block was flipped over and the process repeated on the bottom.  This is way easier than I thought it would be.  Now it is time for the passages from valve bore to cylinder.





The cylinder block is tilted 17.5 ? using a protractor.  Close enough is good enough for this angle.  In order to be sure that the passages are on center with the valve, an edge of the rod is located and then the table offset to the center of the bar.  The parts are drilled 5/64" to intersect the cylinder bore.  I drilled 5 holes, one on center and then two more offset .080" and .160" to the rear and two more offset to the front.  This process was the repeated for each of the valve bores and my mother's brother preferred to be called "Robert" but you get the idea. 

I made the top cover yesterday so now it is on to the bottom cover and the exhaust port.  Most engines of this type have an elevated base and the exhaust pipe exits straight down through the base.  I would rather take the exhaust out horizontally under the engine through the side of the bottom cover.  I milled the rebate on the bottom cover  and then drilled two intersecting holes in the bottom cover.  I got a picture of this setup.

But then disaster struck.  While reviewing the picture on the camera, I dropped the camera.  My lightning quick reflexes took control of my right foot and moved it to catch the camera before it hit the floor.  I missed it by "that! much."  A fraction of a second too late, instead of catching it, I kicked it across the shop, bouncing off of two walls and the floor, causing it too enter an endless sleep.  I don't think it will recover.  I was able to retrieve all of the previous pictures to my computer but that last picture was lost.

I went to the house to borrow my wife's camera, at the cost of some future service to be rendered.  I returned to the shop and proceeded to make the head for the top end and the piston rod guide for the other end.  The piston rod guide is cast iron and the head is brass.  It needs a little more profiling, and I'm not sure I like the brass on this engine so it may be redone. These were straight forward lathe operations and I got no pictures. I did get a few pictures of the various parts in rough assembly position.







Tomorrow's job is drilling and tapping, LOTS of drilling and tapping.  If I survive that with my sanity intact, I will post some pictures tomorrow.  Think positive thoughts.  It could help.

Jerry 
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Offline zeeprogrammer

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Re: four Valve Non-Releasing Steam Engine
« Reply #10 on: September 03, 2012, 04:49:15 AM »
That looks great.
Sorry about the camera. "Future service"...I like that.
Nothing but positive thoughts here.
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Offline Captain Jerry

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Re: Four Valve Non-Releasing Steam Engine
« Reply #11 on: September 04, 2012, 12:41:42 AM »

New plan for the day.  Drilling and tapping takes patience and calm nerves.  There are more than 60 holes of #2 or smaller in the cylinder block alone, and a like number of clearance holes in the heads, valve covers, and wrist pivot plate.  Today was not the day! 

My #2 grandson and his wife arrived for breakfast, bringing Krispy Kreme chocolate covered donuts and news of a third great-grandchild scheduled for March.  A second pot of coffee and a few donuts and my hope for a calm day disappeared.  After they left and I got to the shop, I was too wired for fiddly work.

So I did something else.  The trunk guide has been rattling around in the back of my head, trying to get comfortable.  I have never made a trunk guide before and had only a general plan of operation, but today, I had no fear.  I was so jazzed on coffee that I was almost finished before I realized that I hadn't taken pictures.  I'll try to describe the steps.

I used my table saw to get aluminum stock to rough size.  1.25+" x 1.25+" x 2.125+".   A 4 jaw lathe chuck might have been usefull now but I don't have one so I set it up between centers to turn it into a cylinder 1.25"diameter x 2.125" long.  Now, I could hold it in the 3-jaw and using a progression of bits, open the bore to .625".  Then I had to deal with the details of each end.  The crankcase end has a spigot that joins it to the crankcase that is .750" diameter, and the cylinder end has a .750" diameter recess that joins with the rod end head/piston rod guide.  These must be turned while the part is 1.25" diameter, so it can be held in the 3-jaw, without tailstock support.

With these two features done, the part was put back between centers and the body turned to .825" diameter, leaving flanges at either end.

The final operation was to cut the slot on the front side and the maintenance holes on the backside.  On to the mill, centered and located.  The slot is cut with a .25" end mill and is 1.5" long ( 1.25" center to center) and the the edges beveled using a .375" round nose end mill.

That all. Nothing really spectacular or unusual.  This is what It looks like:







The disk in the last picture is from the scrap box. It is 3" diameter.  It looks to small.  I think it needs to be at least 5" diameter.  Opinions Please!

Sorry about the lack of pictures.  I just got rolling and forgot about you.  My bad.

Jerry
« Last Edit: September 04, 2012, 01:35:34 AM by Captain Jerry »
NOTARY SOJAK

There are things that you can do and some things you can't do. Don't worry about it. try it anyway.

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Re: four Valve Non-Releasing Steam Engine
« Reply #12 on: September 04, 2012, 12:52:41 AM »
Congrats on the Great Grandchild addition Capt!   The engine can wait!

Dave

"Mister M'Andrew, don't you think steam spoils romance at sea?"
Damned ijjit!

Offline Maryak

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Re: Four Valve Non-Releasing Steam Engine
« Reply #13 on: September 04, 2012, 02:39:21 AM »
CJ,

Congratulations GGP....again.  :NotWorthy:

I agree about the flywheel, looks like it should be bigger say 4" dia, also most of them seemed to have a fairly large axial width and heavy rim relative to the diameter.

Best Regards
Bob
Если вы у Тетушки были яйца, она была бы Дядюшкой

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Re: Four Valve Non-Releasing Steam Engine
« Reply #14 on: September 04, 2012, 02:43:18 AM »
CJ,

Congratulations GGP....again.  :NotWorthy:

I agree about the flywheel, looks like it should be bigger say 4" dia, also most of them seemed to have a fairly large axial width and heavy rim relative to the diameter.

Best Regards
Bob

ditto!

Dave
"Mister M'Andrew, don't you think steam spoils romance at sea?"
Damned ijjit!

 

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