1 Steam Cars : Phorum
General Steam Car topics
Definition please
Posted by: jim reed (IP Logged)
Date: September 03, 2002 03:29PM
<HTML>I am a neophyte in the world of steam as my previous posts probably have made clear. This may be a dumb question but when does a steam power plant cross the line from being a low speed, low temp, low pressure unit into the area of high speed, high temp and high pressure?
My previous experience with steam has been through model engineering of traditional engines plus the ownership of a 1900-01 Locomobile engine and an antique 3hp launch engine. All boilers I have used were fire tube designs.
My knowledge of steam mechanics is very basic. Most of what I read on your site is far advanced from where I am at knowledge wise. Not until I decided to build the R.J. Smith bash valve uniflow kart engine with flash boiler did I realize I was moving into an area of which I have very little understanding.
Regards, Jim Reed</HTML>
My previous experience with steam has been through model engineering of traditional engines plus the ownership of a 1900-01 Locomobile engine and an antique 3hp launch engine. All boilers I have used were fire tube designs.
My knowledge of steam mechanics is very basic. Most of what I read on your site is far advanced from where I am at knowledge wise. Not until I decided to build the R.J. Smith bash valve uniflow kart engine with flash boiler did I realize I was moving into an area of which I have very little understanding.
Regards, Jim Reed</HTML>
Re: Definition please
Posted by: Terry Williams (IP Logged)
Date: September 03, 2002 05:57PM
<HTML>I think you have asked a question that is going to result in several subjective answers. To a heating boiler person, 100 psi is high pressure. To a hobby steam boat person, 300 psi (or a little less) and up is high pressure. To a steam car person, 300 psi is probably low pressure. And so on. But I expect most would consider 1000 psi and up in a reciprocating engine high pressure.
Same thing goes with engine speed, it's relative to what you are doing. Steam locomotives run slow, as do most direct drive boats, a few hundred RPM. Small steam hydroplanes like to run at least 10,000 RPM.
When you exceed the lubricating capabililties of conventional steam cylinder oil, around 800 degrees F. or so, I would say that you are heading into high temperatures.</HTML>
Same thing goes with engine speed, it's relative to what you are doing. Steam locomotives run slow, as do most direct drive boats, a few hundred RPM. Small steam hydroplanes like to run at least 10,000 RPM.
When you exceed the lubricating capabililties of conventional steam cylinder oil, around 800 degrees F. or so, I would say that you are heading into high temperatures.</HTML>
Re: Definition please
Posted by: David K. Nergaard (IP Logged)
Date: September 05, 2002 10:59PM
<HTML>In Re Speeds, the classic definition of low speed is less than 150 rpm., or a speed suitable for Corliss and other releasing valve gears. Most locomotives produce their maximum power at or below 300 rpm., although they may run faster on occasion. For good efficiency in an engine of automotive sze, I would say that 1000 rpm. is high, it is very hard to get decent breathing in short cutoff at that speed. 73 DK</HTML>
Re: Definition please
Posted by: Rolly Evans (IP Logged)
Date: September 06, 2002 09:55AM
<HTML>It is all in the design. A two by two engine running at 2000 rpm will have a piston speed of less then 700 feet per min. A rolling mill engine with a five ft stroke running at 200 rpm will have a piston speed of 2000 ft per min. Breathing and port area is a function of design. A four-inch bore Stanley engine is not the best in port design with an area of only .625 Sq inch. If you apply Doble formula for port area it would be 1 Sq inch, Herreshoff would make it 1.4</HTML>
Re: Definition please
Posted by: George Nutz (IP Logged)
Date: September 06, 2002 01:44PM
<HTML> You are right on Rolly. The Doble simple 4"X5" DA engine achieved minimum steam rate and heat rate at 800fpm, or 960 rpm, maximum horsepower at about 1300 rpm. It is all in the breathability of the engine, getting the stuff in and out. If memory serves me correctly the equivalent port diameter of the Stanley 4X5 is 9/16ths" as far as frictional flow resistance---very small in reality. That narrow rectangular slit/port has a lot of flow resistance.
George</HTML>
George</HTML>
Re: Definition please
Posted by: Pat Farrell (IP Logged)
Date: September 07, 2002 02:17AM
<HTML>Does David Nergaard's Stanley piston valve cylinder castings have any bigger of a port diameter than Stanleys original slide valve?</HTML>
Re: Definition please
Posted by: George Nutz (IP Logged)
Date: September 07, 2002 10:33AM
<HTML>Pat,
I believe they are somewhat bigger, Dave could tell you but is at the SACA National meeting this weekend. It has a 1.375" piston valve and the valve sleeve has 8-5/16ths or 3/8" square ports in it. It certainly runs very well and he won our SACA/NE time trials in 14.64 seconds, very good for a heavy condensing car. He also had it up to 58mph in a burst last week and that is very good considering his 4GPH firing rate. Send Dave an e-mail and am sure he will fill you in on everything.
George</HTML>
I believe they are somewhat bigger, Dave could tell you but is at the SACA National meeting this weekend. It has a 1.375" piston valve and the valve sleeve has 8-5/16ths or 3/8" square ports in it. It certainly runs very well and he won our SACA/NE time trials in 14.64 seconds, very good for a heavy condensing car. He also had it up to 58mph in a burst last week and that is very good considering his 4GPH firing rate. Send Dave an e-mail and am sure he will fill you in on everything.
George</HTML>
Re: Definition please
Posted by: David K Nergaard (IP Logged)
Date: September 07, 2002 10:11PM
<HTML>The port size during admission is 20% bigger than in a Stanley block. During exhaust, where the valve over travels the port, it is 40% bigger.</HTML>
Re: Definition please
Posted by: Peter Heid (IP Logged)
Date: September 17, 2002 07:14PM
<HTML>Although all the answers cover the question, I couldn't leave this one alone. The answer has changed much over the years and a time line showing the pressure/temperature ranges used could be quite interesting. In the very early days pressure ment the steam moved into the cylinder an the vacuum of condensation did most of the work. When pressure began to be used to do work, 50 PSI might have been a tall figure. As time moved on the pressures climbed and by 1930 supercritical pressures had been acheived. the modern definition of pressures for power plants came forth at this time with low pressure up to 500 lbs, medium reached 1500, and high pressures upto 3208.2, while supercritical is any thing beyond. Most books vary but for power stations they were in this range. Of course, as it has been pointed out, the application will also help define the working ranges and a time line could made for many applications.
Peter Heid</HTML>
Peter Heid</HTML>
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