STEAM ENGINE R.P.M.

[kiwimodeller]

Having established in earlier postings that we are aiming for around 100 (loaded) to 150 (unloaded) paddle wheel rpm can anybody reccomend what sort of engine revs we should aim to run a fairly large single cylinder double acting engine at? I have an engine built to plans by A.H. Rayman from Model Engineer of many years ago and am trying to figure out what gear ratio to install now I am putting it in to a large (80" long) paddler. The wheels are 6" diameter. It was called a "High Speed Steam Engine" in the plans and alternative Flash Steam and conventional boiler designs were given so it is probably capable of quite high revs but I seem to remember reading somewhere that a much higher volume of steam is required to run at high revs. I am guessing that one would get better throttle control at higher revs as the volume of steam would be varied by a larger amount but I am still keen to get as long a run time as possible too. Any suggestions of ratios most welcome. Thanks, Ian.

[anth]

100-150 rpm is more for full size to larger models.
Anything with a small stroke and bore and especially a single cylinder won't be happy running this low without a huge fly wheel to store what little amount of energy these small models have.
small models are quite happy to rev as it helps with torque and steam consumption as lower revs means what little kj are in the steam is wasted keeping the cylinders warm and not pushing the piston hence condensation.
cheers anthony

[kiwimodeller]

I understood from Eddie and others that the ideal paddlewheel revs for a model was around 150 RPM unloaded which translated to around 100RPM when in the water?  What I am now trying to figure out is what ratio to gear the engine to the wheel shaft. Should I aim for 400 engine revs, 1000 engine revs or Thanks, Ian.

[anth]

not sure if this will be of any help but since most models are moded on full sized then protypical speed would want to be achieved.
Most run there engines at a 4 -1 ratio,but once again as you mentioned steam consumption.
If you are running a high speed steam engine i would be certain the valve gear has  earlyer cutoff to allow better steam expansion.
other wise a larger boiler would be needed of higher pressure's

hope this help cheers anthony

[derekwarner_decoy]

Hi PD's... Ian.. the extract below is from the ANTON website from our PD links - it is the only qualified comment by a manufacturer [that I am aware] where a recommendation of speed & final paddle shaft RPM is offered/mooted

If you read more into this you could see that small [2>5cc] steam engines may offer up to 3000 unloaded RPM @ say 3 Bar..... read more  :computer you will enjoy........regards Derek..
 

 The engine “Quartz” is a product news generation of workshops ANTÓN.
Of simple design and use, this engine is particularly advised
for initiation with the propulsion vapor.
It is a piston valve engine with rotary reverser of walk, which allows walk before/back, the stop and the idle with only one servo of radio order.

This engine, in its horizontal version, is particularly adapted to the propulsion of paddle boats (side or back). The installation of the engine will be done with a reduction of a ratio from 6 to 8 (cratée belt or pinion).

This engine will be used in boats of 5à 10kgrs, with wheels of Ø100 with 150 Misters.