STEAM VALVES AND THROTTLES

[kiwimodeller]

Hi, I finally got my big ("80") paddler running reliably yesterday and have posted some pics in a new photo gallery but as is tio be expected there are some teething problems. The throttle that came with the engine and is made to the design on the plans is a rod about 3/16" in diameter with a taper on the end which goes in to a brass fitting to cut off the steam flow. It seems fairly ineffective and as the boat is bloody fast this is a bit of a problem when it comes to ending the run. I did manage to adjust the servo linkage to where it almost completely shut the engine down on the bench but it then caused a stall on the water and there still seemed to be a long delay between moving the control and having any effect on the engine. Is this the best design of throttle? Maybe it just needs a longer, more gradual taper? Which brings me to the next question - I was given by a fellow member a small valve which has a rotary disc inside with a cutout  to control steam flow. I used this valve to control the steam whistle as it has 1/8" tubing which matches the whistle. It blows the whistle fine but will not completely shut off even when hard back against the internal stop so there is always a dribble of steam out of the whistle. Have I got the wrong sort of valve for this job too? any suggestions welcome, cheers, Ian.

[bogstandard]

It sounds to me that what you are trying to work with is just a steam shutoff valve, not a throttle control valve at all.
If you look at my build of a piston valve engine, in there somewhere towards the end are the designs for a fwd/rev throttle control.
I have found that it works very well indeed and there is no steam leakage at all. Maybe that could solve your problems.
This will only work with either an oscillator or piston valve engine, I couldn't see what type of engine is in your model because of the picture size.

John

[malcolmbeak]

Hello Ian
With a bit of luck you should find a couple of roughish drawings of regulator designs that I have been using sucessfully for geting on for 20 years. The designs are obviously much smaller than you need, but can be easily scaled up.

You will see that on the linear one, I don't use a tapered rod into a hole to regulate and shut off the steam. Shut off is achieved with the "approx 1/32 rad" pushing into the sharp edge of the drilled hole - sounds horrible, but works well. You will see that the rod working in the 3/32 hole is only 90 thou. This leaves space for enough steam to get through for the engine to tick over. Although not dimentioned, there should be a short length left parallel before the filed curve which obviously controls the amount of steam to the engine. It seemed to me to be easier to experiment with the rate of opening this way rather than to taper the rod.

The round regulator has a couple of features that I havn't come across on other designs. 1 The actual valve plate is separte from the operating spindle and should be an easy fit on the two driving pins, and is held firmly onto the valve face by the steam pressure. 2 The nick filed into the leading edge of the steam transfer hole can be experimented with to get a nice gentle control when starting of slowing.

I wonder what engine you are using - is it that Alan Rayman design?
I think I can only send one drawing at a time so here's the first

Regards  Malcolm

[malcolmbeak]

Hello again

Here is the second drawing - this time for the rotary regulator

Malcolm

[kiwimodeller]

Thanks both for your interest. John it is a slide valve single and I am not going to try reversing it as it does not have the necessary linkage on the valve gear. If I decide I need reverse then I have a gearbox I can put in the driveline.
Malcolm, yes it is the Rayman engine which is probably not the ideal paddler engine but it is what I had. You may recall I was keen to try it in a flash steam hydro but you persuaded me to be sensible! I will download your designs but before I make one will talk to a certain Scotsman. It seems the other valve I have (the rotary disc one) came from Oban and is probably meant to be used as a throttle. It is a nice piece of work but I am not sure if the size will be suitable for a larger engine like this so will ask Sandy. If it solves the throttle problem then I will just need a valve which is straight on/off for the whistle so I might be able to modify my tapered one to a rounded end as you suggest. The third channel on my radio is just a switch so I do not have fine control of the servo but with adjustable springs on the linkage at the valve I can allow it to overthrow and keep tension on the valve when shut. Will keep you posted, cheers, Ian.

[kiwimodeller]

After some advice from Sandy I connected up his control valve for the whistle the right way round and Hey Presto it works fine although occaisionally the whistle will still blow all by itself, possibly due to servo flutter. I altered the profile of the rod type throotle valve as per Malcolm's reccomendation and it was slightly better but it looks likeI will have to go to a rotary valve to get proper control. Still, a fun days sailing and I am well chuffed with how it goes. Cheers, Ian.