Steam Engine Correspondence/Damien Gendron

Main > Energy > Steam Engine

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Mark Norton, July 1, 2011

Hi Damien:

I got your request to join the Pivotal Steam Engine project. I appreciate your interest in the project.

I've looked over your background based on what you've posted at http://opensourceecology.org/wiki/Damien_Gendron and your many postings to the forum. Given the variety of your experience and skill set, I was wondering how you'd like to contribute to the project?

I kinda stumbled into leading this project. When I first got involved with OSE back in April, Marcin and I explored several areas of potential contribution. He was keen to re-start the steam engine project after it stalled last year, so I started sourcing parts for the engine. This led to discussions about the design and I started doing design sketches and diagrams. Next thing you know, the whole baby is firmly in my lap. I guess I could have said no at any point along the way, but frankly I was enjoying the process.

That said, I've never built a steam engine or anything even close to it. I do have an education in engineering (master's degree), though it's been slanted towards computer science for most of my career. While that gives me some of the academic tools needed to do this (along with project management experience), it doesn't include any practical experience with the object at hand: a modern (sic) steam engine.

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The project is at an interesting point. The bump valve controlled steam engine design is largely complete. Almost all of the 2D technical drawings and CAD files are complete at this point. Andrew Buck was of some help in this regard, but he seems to have disappeared in the past month or so. He was doing the CAD work, but since he kinda dropped that ball, I took it on myself. I have some experience with 3D graphics applications (Poser, Bryce, Carerra, others), so learning something like FreeCAD wasn't all that difficult. While FreeCAD is very limited, I haven't come across anything that prevents me from modeling the steam engine parts.

I expect the CAD work and design work to be complete quite soon. In theory, the engine is about ready to be prototyped. In practice, I have doubts about this design. Andrew pointed out several flaws that I've given thought to and come to agree with. These can be summed in two main points:

• Lack of variable cut-off
• Compression of spent steam

The bump valve controller, by it's nature, has a fixed cut-in (opening of the steam valve) and cut-off (closing the valve), purely based on the position of the piston in the cylinder. Because the length of the pins on the piston face are fixed, cut-off time is also fixed. Controlled variable cut-off would provide control over the speed of the engine

Compression of the spent steam has to do with the fact that steam is exhausted from the cylinder at the end of the cycle, but revealing holes in the cylinder wall. Steam is vented into an exhaust plenum while the holes are uncovered by the piston. Because these holes are in a fixed place, there is also a fixed amount of time when steam vents. As the piston travels forward, it re-compresses what ever steam is left in the cylinder. Andrew believed (and I agree) that this compress will greatly reduce the amount of work that the engine does, lowering it's efficiency considerably. The White Cliffs engine utilized a vacuum on the exhaust vent to eliminate this problem.

Gregor proposed an alternative design that solves both of the above problems. You can see a cut-away view of a rotating valve control mechanism at http://opensourceecology.org/wiki/Steam_Engine_Design/Rotating_Valve. In this model, steam admission is managed by a rotating valve controlled by a stepper motor under computer control (arduino, etc.). There is a similar control for the exhaust - both at the top of the cylinder.

This design is both simpler and more complex. The control valves are quite simple and easy to make. The stepper motors are off-the-shelf, but would add a fair bit of cost to the engine. Complexity is added by requiring a computer to control the valve timing, but this control gives us quite a bit of flexibility as well.

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So that's the status of the project as of this morning (I living in upstate NY, three timezones later than you). I haven't proposed the design changes to Marcin yet. I'm not sure how he will react, since he REALLY wants to build this thing in the next month or so. Redesigning the engine at this point will delay prototyping, but what good would it do to build a poor or limited design?

Regarding your contribution to this project. I need someone to review both designs in detail. Ideally, this should be done by a steam engine expert, but there are questions that you might be able to provide some input on:

• How easy is this design to fabricate?
• Will steam leak out of seams or joints? Does it need seals of some kind? If so, what?
• Are the parts over-engineered? Are they too heavy? How could things be made lighter?
• Will the crankshaft assembly work as designed? How much vibration is likely based on this design?
• Where are the wear and failure points in the design? How long will the engine last?
• Can the engine handle high pressure, super heated steam? 500+ PSI, 500+ degrees.
• What safety considerations should we be making?

Are you interested in fabricating parts for the engine or perhaps building one yourself? I think even a scale model or a full-scale model in wood, plastic or foam might verify the design.

- Mark Norton

Damien Gendron, July 2, 2011

I must say before going on that there isn't much about this project or OSE in general that I find practical. I am here because I want to get to know you and others in the group. My interest is in forming relationships with like minded folks like yourself, regardless of the task at hand. Keep this in mind when you read my responses.

My vision is to just be a part of the project. I'm sure I can be useful to you. However, I also know very little about steam driven engines. Ideally, someone more experienced in this arena would be guiding us. The likelihood of us coming up with something great in a short period of time is slim to non....:) You must know this already....no? But, we will learn about each other and develop a process that will be useful in the future I'm sure. So here comes some ramblings.

The design as it stands has many shortcomings. On one hand it is relatively simple which certainly needs to be, but at the same time is not likely to produce much power or be very durable. Eventually, after many prototypes, there will need to be some sort of happy point between efficiency and complexity.

Andrew makes some good points regarding the valving. I can add a few more. One problem with this sort of arrangement is the valve opens before TDC (top dead center). This may be fine at high RPM but really bad at relatively low RPM. The piston is on it's way up and suddenly the steam starts to enter before it's ready to go down again. So for part of the stroke, you're fighting against high pressure steam. Combine that with the fact that the exhaust port does not fully evacuate the "spent" steam and you have a problem.

I would avoid the double pin design either way. It would be very hard to insure an even amount of pressure from both sides. This would lead to piston rocking and premature failures. A single centered valve is better. Also, put the pin in the valve not the piston. I would just have a hardened contact point on the piston.

I suspect that this general design would only be good for very short stroked, very high RPM applications. The higher the RPM the tighter the tolerances need to be to get any useful life out of the engine. Also, in the steam world, short stroke means very low HP. Not a direction we want to go in I suspect.

Some general goals might be:

• Low RPM - Long life, design less critical
• Large diameter piston - more torque, need less stroke for same amount of work being done
• Adjustable valving - need to be able to move the valve timing where we need it to be
• Simple construction - it will be nearly impossible for "the Farm" to build it otherwise

I would seriously look at trying to use off the shelf components as much as possible. What about converting a small compressor instead of making it all from scratch? This would get us up and running relatively quickly and give us the opportunity to learn about all aspects of steam without reinventing the wheel. We could then take this knowledge and start looking at scratch build ideas as time permits.

The techy in me says yes to electronic valving. The practical side says hell no. "We" are undecided....:)

  * How easy is this design to fabricate?

Compared to other designs, much easier. Can a guy off the street walk into a fully outfitted shop and build this. Not likely.

  * Will steam leak out of seams or joints?  Does it need seals of some kind?  If so, what?

High pressure steam needs to be used very carefully. It is very dangerous. A leak can easily cut the flesh off a finger in seconds never mind the associated burns. Pipe fittings must be used at all the joints and gaskets between mating surfaces.

  * Are the parts over-engineered?  Are they too heavy?  How could things be made lighter?

If we keep the RPM down the weight is much less critical. I haven't seen any dimensions yet so can not comment much more.

  * Will the crankshaft assembly work as designed?  How much vibration is likely based on this design?

Again, low RPM is your friend here. But a counterweight will likely be needed

  * Where are the wear and failure points in the design?  How long will the engine last?

Low RPM good again. Engine like this will need constant attention compared to what we are used to with a Honda gas engine. Rather than trying to make it last forever make it easy to repair maybe. The basic parts of any steam engine can last a very long time. Keep in mind, the early locomotives spent more time in the shop than running. It was normal back then.

  * Can the engine handle high pressure, super heated steam? 500+ PSI, 500+ degrees.

Probably not that high no. You would need a very small valve at those pressures. The piston would never get the valve open with that kind of back pressure. The higher the numbers here the better efficiency we will see from the system as a whole.

  * What safety considerations should we be making?

That kind of pressure can kill. I would avoid it.

To conclude, hobby engineers with years of steam experience take months to build their engines. This is with a shop full of proper machining equipment at their side and the knowledge to use them. Even if I were to build this, which I haven't decided on yet, it would take me months in my spare time.

I hope you find my comments useful.

Damien

Mark Norton, July 3, 2011

Thank you for your candid comments, Damien. Most of them are not far off of my own assessments. Do you mind if I post these comments to the wiki? I can redact your name, if you like.

- Mark

Damien Gendron, July 3, 2011

You're welcome.

I have no objections to the posting. Perhaps some editing is in order but I will leave that to you. Yes please include my name.

Damien

Mark Norton, July 3, 2011

I haven't gotten around to posting your review, but be assured that I will.

Here is a different question. If we assume (per your recommendations), that the engine will be designed for low pressure (150 psi?) and low RPMs:

  1. How much torque would we need for the control motors described in http://opensourceecology.org/wiki/Steam_Engine_Design/Rotating_Valve? 
  2. Could you find relatively inexpensive stepper motors (or similar computer controlled motor) that would suffice for the design? 
  3. How much would they cost?
  4. How would we create a seal in the rotating valve that would prevent steam from escaping? 
  5. Do we need to worry about this?
  6. How would such a designed be optimized for power output?

This is an attempt to start exploring alternatives to the current bump valve design, which (as you point out) has some fundamental flaws.

- Mark Norton

Damien Gendron, July 3, 2011

I posted the bulk of your comments to Steam Engine Reviews. If you have any changes to make or additions to add, please edit the page directly, though do let me know so I can see them.

Damien Gendron, July 10, 2011

Sorry for the delay Mark. Life got busy for a moment there....:)

> Here is a different question. If we assume (per your recommendations), that the engine will be designed for low pressure (150 psi?) and low RPMs: > > 1. How much torque would we need for the control motors described > in > http://opensourceecology.org/wiki/Steam_Engine_Design/Rotating_Valve? >

Good question. Many things would have to be taken into consideration. If it turned on nice bearings and the seals didn't add too much resistance I would think the torque needs would be very little. Any NEMA sized stepper would do.

> > 1. Could you find relatively inexpensive stepper motors (or similar > computer controlled motor) that would suffice for the design? >

I think so.

> 1. How much would they cost? >

SmallNEMA standard steppers start at around $60 if memory serves me right.

> 1. How would we create a seal in the rotating valve that would > prevent steam from escaping? >

Sealing the drive shaft would be easy but sealing the cylindrical valving part will be much more difficult. Very tight tolerances would need to be used. The guts of a standard ball valve might do the trick. The ball would seal better than a cylinder shape.

> > 1. Do we need to worry about this? >

At some point, as the feed pressure is increased, this sort of valve will fail. For low pressure systems it would be fine.

> 1. How would such a designed be optimized for power output? >

Valve timing is important. Using "spent" steam again in a secondary cylinder would add to efficiency. Simply put, piston diameter provides the torque and piston stroke gives you horse power. There's no replacement for displacement. I'm sure there's a preferred ratio between diameter and stroke.

Mark Norton, July 10, 2011

Damien:

Regarding the torque needed to turn the valve under pressure, I think that this is a crucial question to this design. How can we either calculate the forces needed or experiment to determine them?

I thought about using a ball valve. You are right that they are very common and inexpensive. However, the ball valves I am familiar with (mostly water valves) seem to require quite a bit of torque to open and close them. Furthermore, they are restricted in range of motion and direction (though I would think this could be subverted). Most have a teflon coating as a bearing surface. Would this break down under steam heat?

Using "spent" steam again in a secondary cylinder would add to efficiency.

You are describing a "Condensing Steam Engine". I agree that it would add considerably to the efficiency. The current design doesn't preclude secondary and tertiary expansion cylinders, though the timing of such assemblies is important. Such an engine is more complex than a single cylinder. I'd like to focus on the simpler solutions first, even if not as optimal as more complex solutions. Naturally, such "simpler" solutions need to be sufficiently powerful and efficient to be worth the trouble to build them.

- Mark Norton

Damien Gendron, July 10, 2011

Regarding the torque needed to turn the valve under pressure, I think that this is a crucial question to this design.  How can we either calculate the forces needed or experiment to determine them?

I thought about using a ball valve.  You are right that they are very common and inexpensive.  However, the ball valves I am familiar with (mostly water valves) seem to require quite a bit of torque to open and close them.  Furthermore, they are restricted in range of motion and direction (though I would think this could be subverted).  Most have a teflon coating as a bearing surface.  Would this break down under steam heat? 

There are many different ball valves out there. Yes, the more common ones have some sort of Nylon/Teflon insert in them. There are also valves that are solid stainless steel inside. If it's actually Teflon inside, no problem. Teflon is a high temperature plastic. Very durable also. The metal valves are easier to rotate.

If the rotational force seems to be high, we could simply gear down steppers to give them more torque. This is assuming the RPM requirements are not to high.

As for testing, I think you could simply use an inch-pound torque wrench to determine how much force is needed to get the valve going.

Cheers, Damien

Mark Norton, July 10, 2011

> There are also valves that are solid stainless steel inside. The metal valves are easier to rotate.

Could you find some sources on the internet for these? Some prices, also?

- Mark

Damien Gendron, July 11, 2011

Here's just a small sampling of what's out there. These valves are used everywhere in industry so there are many suppliers.

http://www.svf.net/process_and_industrial_valves_1.php#steam_n8

Check out the attachment also

Prices vary wildly. A simple Teflon seated ball valve should be no more than $30-50.

Have a look here:

https://www.industrialzone.com/valves/ball-valves/apollo-valves/

Cheers, Damien

Mark Norton, July 11, 2011

It also occurs to me that wear might be a problem. Are ball valves meant to handle being opened and closed more than once a second? Naturally, wear is a problem regardless.

Price is also a consideration. Two ball valves at $50 contributes $100 towards the cost of the engine.

- Mark

Damien Gendron, July 11, 2011

Well, they are designed to rotate. Any valve will wear in time. The better quality valves will last longer I'm sure. But again, maybe that's not a problem. If you can buy a cheap valve for $25 and it lasts 2 or 3 years and it takes 15 minutes to replace, who cares?

As for adding expense to the bigger project, I think it's relative. If $100 helps to make it 10% more efficient it may be justified by the added power produced.

Once the prototype is built and the design settles down a bit, we can look at bulk purchasing to get the prices down. Lets prove the concept, then worry about making it cheap.