<HTML>Hi Rolly
Thinks for the updates on your Derr Boiler on the SACA froum. I guess it was B&H type boiler. Seams they are simular.
I wound up looking at multi stages because of the valve open close time. I am trying to make electrid valves work. But so far all the electrac valve designs I have found, Take a minum time of around 4 MS. The one design I liked was developed by AURA Systems. They no longer have any info on their site. Seams the have changed directions and into mobol power generation. [
www.aurasystems.com]
The AURA design was an electromagnetic latched valve. You had the valve position held between two compressed springs. Electrico magnatics were located at each end of it's possable trevel. Initially a large curent is needed to pull the valve to one side. But once in contact the current can be reduced and you still have a great retaining force when the metel contects are together. A relese of the holding magnetic and the spring on that side being more compressed then the other forces the valve away toword the other magnetic. The other magnetic is energized with holding curent. Initia caries the valve close enough that it is latched. This system takes minum energy as you are not moveing the valve by the electric energy. Just holding it. Letting the springs do the work. A minum of energy is used pulling it to the contact point.
You don't get a lot of movement and are time limited.
It may be impratical or impossable to do what I am trying to do. But one never knows with out trying. The basic idea is that the most efficienct cycle (On Paper) fully expands the steam to exhaust pressure. That is not really pritical in a positive displacement engine. And in reality it seams the best results are just short of full expansion. There are other considerations. Like space requirements etc. But to get the over all best performance and efficiency every things must be balanced to the optimal. Power requirments make the engine displacement neccessarly large with high expansions. And must balanced with boiler size. High pressure doesn't mean a smaller engine if you utilize most all of it's expansive power.
Over expansion to below exhaust pressure really degreads efficiency rapidly. I a single expansion you can reduce expansion all you wont and avoid over expansion. You get better efficiency over it's power band as you are never over expanding. With any engine you have expansion from the boiler pressure down to the exhaust pressure. Part of which takes place in the engine. Hopefully. For efficiency we would like to see most of that expansion take place in the engine (isentropic). Some expansion will always take place outside the engine contrubuting nothing to the output work of the engine. With a normal compound you have a minum specific volume change set by the stage displacements. Operatoring between any two pressure temperature states also sets a specific volume. So a compound with it's it set in concreat minum volume changes dictates a minum operatoring pressure below which you will go into over expansion. So a compound has a minum power range below which efficiency dwops rapidly. In an automobile ie need a wide power range and a high expansion compound is simply eleminiting it's self with it's nerrow bower band limitation.
Andy</HTML>