Engine Demonstrator Compressor Project

It was suggested we should move a discussion here to avoid cluttering Allan's Stuart Victoria Thread.

The issue under debate is a design for a low pressure but reasonably high volume compressor for demonstrating (unloaded) steam engines.

The basic specification would be a maximum pressure of 10-30 PSI (personally I think 10psi would be ample), a volume sufficient to run a few engines at once, and low noise. Low noise would include ensuring any safety valve or regulator doesn't make loud or sudden hissing noises!

This would suit it to use at exhibitions or even in a domestic setting.

I may be being optimistic, but if a very simple design can be generated through this forum, I'd be happy to publish it in MEW.

Neil

Edited By JasonB on 09/03/2014 19:19:47

How about an old 25cc two stroke, with a non-return valve inplace of the spark plug? (Driven by geared electric motor)

Got those bits...

Steve

Edited By JasonB on 09/03/2014 19:21:02

That's something a few of us could think of, a reasonably small, silent compressor, designed with the powering of model steam engines as its main purpose. Maybe low speed, large volume. I don't think it would need to bemore than, or even as much as 50psi, 30psi would be enough for most engines, it's the volume of air that is important.

Ian S C

Edited By JasonB on 09/03/2014 19:21:41

It's definitely volume of air that's important. Aquarium pumps can produce quite high pressures, but no where near the volume of air. My Victoria will run nicely at 10PSI, so a large piston at low speed and dead quiet would solve a lot of problems, certainly for stationary engine builders.

Low pressure, low speed, means low stress too, so plastics could be used for key components.

Steve

Edited By JasonB on 09/03/2014 19:20:17

The above 3 posts have been moved here from Allan's Thread.

J

Thats virtually the same as one of those 12volt tyre compressors, and noisy as a very noisy thing.

I use an old freezer compressor (suitably de gassed of course).

Neil what do you define "a few engines" as?

Reason for asking is that something like Allan's Victoria will displace 6.3cu in. per rev, the No 1 he intends to do next will displace 12.6cu in. per rev.

I know that my 5 CFM 20lts tank compressor has a job to keep up with my Easton & Anderson beam which displaces 14.4cu in. per rev.

So are we talking a few little wobblers or a few reasonably sized engines, I won't go into traction engines as I know some who need 20cfm compressors to play with them.

J

Edited By jason udall on 09/03/2014 20:43:25

This looks like it will be an interesting thread, especially if it stays simple as Neil suggested. After reading some of the comments about how important the volume of air is I couldn't help but thinking a bit about the Cylinder inlet and output pipe diameters and how and if this affects things very much, also what effect a 90 elbow would have on the inlet / outlet - I was thinking I would use them on my little Victoria. Thinking back to O and A level maths it would have been interesting to have been able to put figures to such things, if only I could remember, I'm sure we did similar type examples!. e.g. I think the compressor airline is 1/4 BSP thread which I think is about 1/2 inch diameter line, the glands on the engine take 1/4 X 32 tpi unions and 5/32" pipe - thats one heck of a step down, even if making a connection directly into the gland and no pipe.. Knowledge of such things I guess would allow some slight tweaking of gland and pipe sizes at the build stage if advantageous for a given setup..

For me It would have been interesting to know that the step down in pipe diameter results in x% decrease in efficiency, likewise x% decrease in having a 90 elbow at the input / outlet for any given psi at the compressor in comparison to a straight connection... Maybe too technical but interesting I think, I have this mad idea that someday I may build a little steam engine to my own design - sorry I've been waffling on a bit - just ignore me..!

Look forward to seeing what people come up with..

Cheers.

Allan.

I suppose one option would be to add a couple of NR valves to your largest model and turn that over with a motor this making it into a pump that would provide air to work the smaller ones. No need for a compressor at all

Hi Jason,

The first job of this thread is to define things like 'few' and get a proper spec.

So some thoughts...

I'm guessing the Victoria would be near the top end for demand. A 10V is less than a cubic inch, and I'd guess most stationary engines would be smaller than the Victoria.

Speed is the main issue, most engines look best at a 'realistic' speed of 60-90 rpm, although many small engines won't run smoothly at less than 120rpm. It's the little 'wobblers' that need to run fast, but they only need a breath of air. How fast do you run the grasshopper, I'm surprised it uses so much air?

1 cubic foot per minute should easily run a dozen 10Vs. My little diaphragm compressor (I'd guess 1cuf/m?) runs a 10V at very scary rpm without difficulty...

The Victoria at 200 rpm should need less than a cubic foot a minute, and to my mind would be running too fast.

But another issue is the benefit of having lots of air in a receiver and keeping a steady pressure so when one engine is added or taken away the others aren't affected. Also, may people like to control speed with bleed valve, rather than restrictors, so air is wasted.

Finally, I do think that, at low pressures of a few psi, slide valves probably don't seal very well and I guess a lot of air gets wasted.

Neil

Hello Walacce, good evening.

Is this the pump you refer to? I had two of them, long time ago...

More pictures to be found ***here***
And two of them working  ***here***

Best regards
Dias Costa

Edited By dcosta on 09/03/2014 21:10:20

This may be bonkers, but:

The "Hydraulic Mains" installed in various cities around 1900 used dead-weight loading of the accumulators, to provide constant pressure. Our system could be pre-pressurised by manually raising the weights ... If the water pushed on a suitable [bicycle pump style?] piston in a sufficiently large tube [plastic soil pipe?] we could supply air in near total silence.

Someone else can do the Math.

MichaelG.

.

Edit: fixed my typo just in time, Thanks to Jason

Edited By Michael Gilligan on 09/03/2014 21:28:08

One idea I have is a piece of 110mm soil pipe with a bung in one end and a diaphragm or piston at the other. the swept area is separated from the bulk of the pipe with a simple flap or reed valve. The bung has an a air outlet and a simple pressure regulator/safety valve. If rated at 10psi and the pipe is vertical the valve could be a loose weight, as used for pressure cookers - with a simple shroud to reduce noise.

It should be possible to make a lightly loaded piston, if the stroke is long enough a port in the side of the pipe would do instead of a valve.

10psi is easily within the capacity of soil pipe (think potato cannons).

Any thoughts on making a piston to run in soil pipe?

Neil