By continuing to use this site, you agree to our use of cookies. Find out more
Forum sponsored by:
Forum sponsored by Allendale Jan 24th

Testing Models

Testing of model steam engines and turbines.

All Topics | Latest Posts

Search for:  in Thread Title in  
Turbine Guy23/10/2020 17:11:40
243 forum posts
134 photos

In a conversation with Mike Tilby, the subject came up about my first turbine project. I helped in the design of a turbine for Lear Motor Corporation. This turbine originally was intended to run on an organic fluid to keep the speed of the turbine lower. None of the efforts to keep the organic fluid from breaking down in the boiler worked, so eventually the design was changed to running on steam. Lear found people talented enough to design and make the bearings, seals, and gears operate at 60,000 rpm. I left Lear Motor Corporation before the turbine was ever tried in a vehicle. I was too young at the time to realize the importance of keeping records of my early projects so I don’t have any of the test results I was involved with in the development of the turbine. In trying to find out the actual output of the turbine, I found the articles shown in the following Lear Bus Link. The articles included in this link have enough information to evaluate the maximum performance of this turbine. I thought I would compare this turbines performance with that of one of Abner Doble’s steam engines that was probably one of the best ever put in a car. I got the test results of the Doble Model E engine from the book ‘Doble Steam Cars, Buses, Lorries, (trucks) and Railcars’ by J. N. Walton. The following table gives the results of this comparison. The Doble test was run June 16, 1928, so even though this engine was made 44 years before the Lear turbine, it had higher efficiency. Neither of my sources told what accessories were included in the tests, so the comparison might be slightly unfair. The water pump alone is a fair amount of power for these mass flows and pressures. I know this is a testing models thread, but I thought some of you might find this interesting.Lear Doble Comparison

Turbine Guy30/10/2020 10:52:02
243 forum posts
134 photos

I have been running my Turbine 3 SD on air trying different combinations of shims on the rotor and clearance between the collar and the outer ball bearing. The best combination was with 7 shims on the rotor and 0.004” spacing between the collar and outer ball bearing. With this combination, I got the highest speed running on air with my EP 2508 propeller of any of my turbines. The speed obtained was 25,000 rpm. The post of 29/07/2020 in this thread showed the results for the test of the Saito T-1 steam engine running on air. The Saito T-1 had the best performance of all my small steam engines running on air or steam. The following chart shows a comparison of Turbine 3 SD and the Saito T-1 steam engine running on my airbrush compressor. Since Turbine 3 SD has turned out to be my best performing turbine and I have only showed the modifications to make the side discharge (SD) in the Model Turbines thread, I will show these changes in the next posts. The post of 27/09/2020 in Model Turbines is the start of the discussion of the change to side discharge.

Air Tests

Turbine Guy30/10/2020 11:11:00
243 forum posts
134 photos

The following drawing shows the dimensions of the nozzle and rotor in turbine 3 to change to side discharge (SD). This drawing also shows the position of the parts that gave the best performance. The position of the new nozzle was the result of trying to add other nozzles that failed by the drill drifting or breaking. This was about the only space left. Ideally the nozzle would be placed at the top of the turbine so that condensed steam would not collect around the nozzle. The next post will show the changes of the rotor to make it side discharge.

Tangential Turbine 3 SD RA

Turbine Guy30/10/2020 11:15:16
243 forum posts
134 photos

The following drawing shows the Turbine 3 rotor modified to side discharge (SD) by removing one row of pockets.

Tangential Rotor 3 SD

Evan Lewis17/11/2020 06:48:17
23 forum posts
10 photos

I found this discussion very interesting. Thank you! I have done some similar calculations for a Hero engine which I documented in a web site that you might find interesting, although I think your knowledge is much more advanced than mine. I am now building a double acting two cylinder steam engine and was interested in the results for different types of piston seals. I will post that separately.

www.HeroSteamEngine.com

Turbine Guy17/11/2020 13:56:21
243 forum posts
134 photos

Hi Evan,

I’m glad you found this thread interesting. Those of us that go so deeply into the details, are a very small minority. I followed your link and found your discussion of the Hero turbine very enlightening. What you found in trying to find the best compromise between leakage and friction will be your biggest challenge with the piston seals. I have discussed in this thread tests of several small steam engines with different piston seals you might find useful. Most of these tests were with air since it was much easier to setup, eliminated the effect of moisture content, and the output of my airbrush compressor was more consistent. If you run on air and lubricate the engine by putting a few drops of oil into the inlet before starting your test, you can only run a short time before the oil escapes. Packing that absorbs the oil will extend the useable run time. My tests with steam and the displacement lubricators indicated that they work for much longer run times. I look forward to what you find in your testing of the piston seals.

Keep up the good work,

Byron

Evan Lewis18/11/2020 10:36:07
23 forum posts
10 photos

Hi Byron,

Thanks for your reply. I was interested in a comment in the thread that the turbine jets go "sonic" at 25 psi. I suppose this is the pressure at which the fluid velocity reaches the speed of sound and cannot go any faster. Is that correct. I did similar calculations for the Hero engine and concluded that it occurred at 10-14 psi but I may not have taken into account all the factors such as the increase in density as pressure increases. I was very surprised that it occurs at such a low pressure even if is 25 psi. Because the Greeks probably could not deal with high pressures my Hero engine had a pressure relief valve set at 15 psi.

Are you able to explain in simple terms why the Hero reactive turbine is so much less efficient than other turbines which are so efficient that they are used in nearly all oper stations. I wrote an article on the history of a local engineering company, A&G Price and they claimed that their Pelton wheels were 90% efficient. Using the data they provided I checked their calculation and it was correct, but I don't know how reliable their data was.

I have started building a double acting 2 cylinder horizontal steam engine from scrap metal using only a lathe. I put a post under the heading "Stationary Steam Engines". I read the above posts about measuring the effectiveness of piston seals under pressure. For simplicity I am thinking of using O-rings for piston seals. To keep friction down I understand they would be fitted loosely. I imaging they should only just touch the cylinder walls with no perceptible compression. Is that right? The main cylinders are 22mm diameter so I would by O-rings with 22mm outside diameter but they are sold by inside diameter so 18mm rings 2mm thick would do it. Is that right? Then the grooves would be 2mm deep I think.

I am using pistons as valves instead of the usual flat plate so that I can do it easily on the lathe. The valve cylinder is penetrated by numerous ports: 2 steam inlets, two exhaust ports, and two ports leading to the top of the main power cylinder. They are round holes drilled rather than slots. Can I use rings on these valve pistons too or will they get torn up by the ports? Ideally the valve pistons should seal along their whole length but two O-rings or any other kind of rings would not do that.

Our hardware shop says they can get two kinds of O-ring: Nitrile eg N70 which are recommended for temperatures up to 90 degrees C, and red Vitron up to 200C. I assume I would need the Vitron type.

You may not want to read more and this is just an aside: I bought a BMW X5 second hand at 100,000km. It leaked water like crazy but passed a pressure test by three different organizations including AA. My radiator man found that it had 5 O-rings from China that had gone soft and gummy, completely flattened. Replacing them fixed the problem and he said this was very common with Chinese O-rings. But why did it pass pressure tests? They were associated with the expansion chamber which is part of the pressurized system. I think they must seal under pressure and leak when the pressure drops.

Thanks for your help.

Evan

Evan Lewis18/11/2020 10:42:21
23 forum posts
10 photos

Hi Byron,

I was interested in your mention of Doble: "I thought I would compare this turbines performance with that of one of Abner Doble’s steam engines that was probably one of the best ever put in a car. ". The engineering Co A&G Price Foundry I was talking about had a license to male Doble steam buses for Auckland City. Would they have been turbines?

Evan

bernard towers18/11/2020 13:02:26
42 forum posts
55 photos

Evan , I think the o rings you are looking for are made from Viton. Just a word of warning, back in the day while still working we received a memo about not touching viton rings that had reached a high enough temp to have changed colour as they were thought to have carsonegenic properties. Not saying don’t use them just be careful.

Turbine Guy18/11/2020 14:27:42
243 forum posts
134 photos

Hi Evan,

I will try to answer the questions from your last two posts partially copied below.

I was interested in a comment in the thread that the turbine jets go "sonic" at 25 psi. It is important to show the pressure as absolute (psia) or gage (psig) and the gas (steam, air, etc.). The critical pressure ratios are 0.528 for air, 0.547 for superheated steam, and 0.577 for saturated steam. For air with the exit pressure being atmospheric (14.7 psia), the inlet pressure would have to be 14.7/0.577= 25.5 psia = 10.8 psig to go sonic.


Are you able to explain in simple terms why the Hero reactive turbine is so much less efficient than other turbines which are so efficient that they are used in nearly all operating stations? The problem with the Hero turbine is the very high speed (approximately twice the speed of an impulse turbine) required to obtain reasonable efficiencies

For simplicity I am thinking of using O-rings for piston seals. To keep friction down I understand they would be fitted loosely. I imaging they should only just touch the cylinder walls with no perceptible compression. Is that right? I tried both floating and light compression of the O-rings. The floating type as described in the follwoing link worked best. Floating O-ring

I am using pistons as valves instead of the usual flat plate so that I can do it easily on the lathe. Can I use rings on these valve pistons too or will they get torn up by the ports? Both of my steam engines that use piston valves rely on a close fit and have very low leakage. Whatever gain you get with seals will probably be offset by the extra friction.


Our hardware shop says they can get two kinds of O-ring: Nitrile eg N70 which are recommended for temperatures up to 90 degrees C, and red Vitron up to 200C. I assume I would need the Vitron type. I used the Viton.

My radiator man found that it had 5 O-rings from China that had gone soft and gummy, completely flattened. But why did it pass pressure tests? If the pressure is enough to move the O-ring, it will press against the sealing surfaces and stop the leakage.

The engineering Co A&G Price Foundry I was talking about had a license to male Doble steam buses for Auckland City. Would they have been turbines? I think the only steam buses tried in California were the Lear turbine. There were other competitors and might have been tried.

Edited By Turbine Guy on 18/11/2020 14:30:33

Turbine Guy18/11/2020 18:07:02
243 forum posts
134 photos

Hi Evan,

The following was copied from the Parker Metric O-ring catalog. It explains the concept of the floating O-ring. In the next post I will show a copy of the table that gives the groove dimensions for the metric floating O-rings.

Metric Floating O-ring 1

Turbine Guy18/11/2020 18:22:42
243 forum posts
134 photos

Hi Evan,

The following table shows the groove dimensions for the 2-115 size O-ring you will need for your 22mm bore. The amount of leakage with the floating O-ring is more than offset with the reduction in friction. You can also use packing in the groove if you want to try that. The pest performing packing I have tried was suggested by Thor. I spun Teflon tape into a thread and wound it into the O-ring groove as tight as I could. When you add oil the small spaces in the packing absorbs some of the oil and it wicks out while running. The wicking of the oil and the lubricity of Teflon reduces the friction considerably.

Metric Floating O-ring 2

Turbine Guy19/11/2020 16:07:26
243 forum posts
134 photos

I updated the table shown in the post of 12/07/2020 to include the tests of the Saito T-1 steam engine. I added a disclaimer to the notes included with the chart that the test power shown for speeds below 1,000 rpm may not be valid. The performance given by APC for their propellers is not shown for speeds below 1,000 rpm but since the power coefficient increases at lower speeds due to the Reynolds number effects, the test power shown should be conservative for the lower speeds.

My Steam Engines 3

All Topics | Latest Posts

Please login to post a reply.

Magazine Locator

Want the latest issue of Model Engineer or Model Engineers' Workshop? Use our magazine locator links to find your nearest stockist!

Find Model Engineer & Model Engineers' Workshop

Latest Forum Posts
Support Our Partners
ChesterUK
Eccentric July 5 2018
EngineDIY
cowells
Warco
emcomachinetools
Eccentric Engineering
Subscription Offer

Latest "For Sale" Ads
Latest "Wanted" Ads
Get In Touch!

Do you want to contact the Model Engineer and Model Engineers' Workshop team?

You can contact us by phone, mail or email about the magazines including becoming a contributor, submitting reader's letters or making queries about articles. You can also get in touch about this website, advertising or other general issues.

Click THIS LINK for full contact details.

For subscription issues please see THIS LINK.

Digital Back Issues

Social Media online

'Like' us on Facebook
Follow us on Facebook

Follow us on Twitter
 Twitter Logo

Pin us on Pinterest