Silly idea for running engines.

[rickharris]

I woke this morning with a nagging thought I can’t get out of my head. I am sure this is a silly idea but can’t see why.

From what I read most people in this business don’t use live steam – for some good reasons – most are using compressed air. Compressors are noisy and not very house friendly.

If you need say 25 Psi to run your engine this could be generated by putting a weight on a piston in a cylinder.

OK:

Say a small wobbler such as Elmers has a swept vol of .32 cu inch (about 5 cc) – we want to run it at 200 RPM. Assuming no losses/leaks(!) it will use some 1000 cc of air a min (1 ltr).

As pressure is related to surface area if we put a 1 lb weight on a piston 4 inches dia it will generate 12.5 PSI – so 2 lbs will produce about 25 PSI 4 lbs about 50 PSI.

A 1 litre volume of dry air under 25 PSI would need to start out at 1.26 ltr (I think!) and would last for about 1 min. (5cc swept x 200rpm).

Recharging the system would only call for lifting the weight. So making such a structure to charge say 5 ltrs to get a run of 5 mins doesn’t seem too difficult.

My mental picture is of several tubes to make up the 5 ltr or what ever you choose– kind of “bicycle pumps” bonded together with the weight on the top. By using a cup valve as in a bike pump sealing is easier and accuracy of build less critical.

Of course a suitable 5 ltr vessel could also be used it’s not that big, about a gallon. A wider vessel would correspondingly require less weight.

Am I totally missing the point and getting it all wrong?? – wouldn’t be the first time

 

[SBWHART]

Not a Silly idea we used something symilar to provide hydrolic pressure to a line of presses, but in this case there were no loses in the system, we just had to pump the pressure up a bit at the start of the shift, if we wanted a higher pressure we just put more weights on top of the cylinder.

Stew

 

[Tin Falcon]

Ricch
I think yo need to check you math.
Tin

 

[ksouers]

Rick,
The one pound weight is evenly distributed across the face of the piston. Yes, the piston has 12.5 in2 surface area. Therefore the pressure is 1lb/12.5 inches. Not 1lbx12.5 inches.

You would need about 315 pounds of weights to get 25 psi.

Otherwise, your reasoning is quite sound and was common practice in the "dark ages" of early science and engineering. Water and mercury were commonly used in laboratories to provide pressures or create vacuums when reliable and accurate pumps weren't available.

Kevin

 

[mklotz]

Yes, your math is completely wrong. As Kevin points out, once you do it correctly you'll see that your scheme is rather impractical.

For small engines, an airbrush compressor is a very viable solution. Since they're meant to be run indoors, they're very quiet. They'll easily produce 15 psi and their cfm is sufficient for all but the largest or most inefficient engines.

Another option is an air "pig" - a portable air tank. Filled from a conventional compressor, they are dead quiet and can provide higher pressures than the airbrush compressor. Their limitation is capacity but, then, your original idea has that drawback as well.

 

[rickharris]

Rick,
The one pound weight is evenly distributed across the face of the piston. Yes, the piston has 12.5 in2 surface area. Therefore the pressure is 1lb/12.5 inches. Not 1lbx12.5 inches.

You would need about 315 pounds of weights to get 25 psi.
...
Kevin

Ah - I said it was early here Mmmm OK think again. ) knew there must be a reason no one was doing this

Thanks for your consideration of my silly idea - there may be more

 

[Noitoen]

I have one of this http://www.jun-air.com/graphics/images/Products/Gallery/Oil-lubricated/02_02_036_B_-_6-25_screen.jpg

It makes less noise than my 2 door "American style" refrigerator. You can almost sleep next to it ;D ;D

 

[Shaynut]

OK, this is the third attempt on this. Every time I do spell ck and finish every thing goes south, SOOOOOOOOOO.
Have been lurking for about a month. I do not have a shop cuz :'( I live in the Philippines right now.
Another good source for air is the weed sprayers from you favoriet Box Store. One to Five gal in size.
Watched a master at the BTS who was given 2 Aristo-crafe live steamers because they would not runn, and this was his source for air. He had hem both sorted out, loosened up and running in a couple hours. ;D
Roland

 

[cfellows]

Hey Roland, Welcome to the forum!

 

[cfellows]

I once made a hand cranked pump using 2 , double acting air cylinders. The crank disks were two gears meshed with each other and the crank throws were 90 degrees apart. The air cylinders had a bore of about 1" and a stroke of close to 3 inches. The hand crank was fastened to the opposite side of one of the gears. I used double ball check valves on each of the air cylinder ends and urethane tubing to connect it all to a manifold. Sorry I don't have a picture and no longer have the pump.

Cranking the handle about 1 revolution per second would drive a small steam engine pretty well. And, with 4 power strokes per revolution, the speed was pretty consistent. It wouldn't have been to much more trouble to power it with a gear motor.

Chuck

 

[tel]

Now I remember why I build boilers. ;D