Hand Cranked Air Compressor

[Robert Hornby]

I would like to try and run a couple of small model engines on air. They work fine at home and need only about 6 psi. from my 240 volt compressor. However I have been asked to show them to my Probus group and give a talk about them and model making in general. It would be nice to have one running but taking an air compressor into our meeting venue would not be really satisfactory. So I was thinking if it would be possible to build a manual hand cranked one specific for the job. I have a 250mm dia. flywheel casting that I could use for the crank wheel.
Robert

[Edward]

Have you got a spare wheel in your car? that'd probably provide enough air to run it for a reasonable time and then you could just pump it up again

[Robert Hornby]

Thanks Edward, But taking a spare wheel into our meeting at the venue would not go down so very well, so I am still looking for ideas for a compressor.
Robert

[steamer]

You could get a compressed air tank from the auto parts store....that might be a better bet....I think you will be pumping for a Very long time with a hand crank...and it's a lot of work for just a demo.....do they have compressed air on the premises?....had to ask

[Brian Rupnow]

I have, in the past, used an ordinary hand operated tire pump to demo my small engines. You don't have any reserve of compressed air, but as long as you pump, the engines will run.---Brian

[jonesie]

i use a small airbrush compressor to run some of mine,maybe you can borrow one from someone ,they are nice and small. just a thought

[Robert Hornby]

Thanks guys for your ideas, I used to have an air brush compressor but it was quite noisy and would detract from the display. My wish to have a hand cranked compressor would also be something the kiddies could turn to get the model to work at the shows and itself would be a sort of model. I only need to generate around 6 or 7 psi. I have searched the internet for a compressor design without luck. I am assuming it only needs to be a cylinder with piston and two flap valves, one inlet and one outlet, or am I being too simplistic?
Robert

[crueby]

I like Brian's idea of a bicycle pump. Plenty of pressure, easy to operate.

[cnr6400]

Robert - in the very old days of hard hat divers hand driven air pumps were used. I have seen some in museums with 24" to 30" cranks on disks at each end, and 2 or 3 cylinders, also some with round-rimmed flywheels to be turned by hand. Later of course small engines and electric motors took over the duty. maybe a modern copy with kid-size cranks and lightweight aluminum cylinders and frame (for easier transportation) might do. Silicone rubber flap valves or thin stainless shim stock multi-leaf "petal" flap valves could be used. Just food for thought.

[steamer]

I like Brian's idea of a bicycle pump. Plenty of pressure, easy to operate.

Me too.    and perhaps an accumulator made from some PVC pipe fittings?....might smooth it out a bit....

Dave

[Charles Lamont]

An oscillating cylinder, or cylinders, would be OK for that sort of pressure. And no need for valves.

[MJM460]

Hi Robert, I wonder what pressure you could achieve with something like a fireside bellows/ small version of a blacksmiths bellows.  Leather flap valves, and flexible sides, or neoprene or similar, plywood construction, long handles to help with the necessary force.  You don’t need much volume.

Alternatively, a hand pump for pumping those hypalon inflatable dingy’s.  About three inches diameter, but like a car tyre pump, easy to get your weight over the handle so you can get the required pressure, which might just work.  (You could try Whitworths if you are near one of their Sydney outlets, or mail order from them.)

The main issue is that even 5 psi, the required force builds quickly as you increase the cross section area of a piston.

MJM460

[Daggers]

Hi,
Just been out in the garden spraying the roses using a hand pressurised garden spray. The one i have is quite large, might be worth a try?

[steamer]

Hi,
Just been out in the garden spraying the roses using a hand pressurised garden spray. The one i have is quite large, might be worth a try?

Brilliant idea!

[cheepo45]

I rigged up a garden sprayer for running my engines - it worked pretty well.
 Scott

[Robert Hornby]

Once again thank you all for the ideas for the manual compressor I am very grateful. I like the idea of using PVC pipe for the receiver and the idea of utilising oscillating cylinders is worth some thought. I'll keep you posted.
Robert

[Daggers]

Have a look a this youtube, it might give you some inspiration.
<a href="https://www.youtube.com/watch?v=pP8dwWxjoFs" target="_blank">http://www.youtube.com/watch?v=pP8dwWxjoFs</a>

[Vixen]

Amazing, somehow, he make the description of a hand pump last four minutes.
I guess the displacement of the pump needs to be larger than the displacement of the engine cylinder.

Mike

[Jasonb]

If you have an oscillating engine then just adding a couple of non return valves to inlet and outlet will turn it into a pump if you turn the flywheel by hand, should be enough to drive a smaller engine.

can of airbrush propellant is easily portable provided you don't have large displacement engines

Or do as I can just blow down a bit of flexi hose.

[Charles Lamont]

If you have an oscillating engine then just adding a couple of non return valves to inlet and outlet will turn it into a pump if you turn the flywheel by hand, should be enough to drive a smaller engine.

What do you need the non-return valves for?

[Jasonb]

Actually you don't as the movement of the cylinder should shut off the port unlike a reciprocating piston.

Seems to work well enough

<a href="https://www.youtube.com/watch?v=66OT9e8WGp8" target="_blank">http://www.youtube.com/watch?v=66OT9e8WGp8</a>

[Zephyrin]

I use now a mini air compressor for nail art, found on ebay or banggood, that delivers 2 bar of air with a flow sufficient for small steam engines, the noise is quite acceptable for a demo in a show, or in the dinning room...

[Robert Hornby]

After a bit (a lot actually) of procrastination I have made a start on my Hand Crank Air Compressor. The main reason for it is to be able to display my small engines running on air rather than just static. With a hand crank compressor I can get the kiddies to crank it so they will be powering the engines, so I have designed it to be very robust and to take a bit of rough handling. it will not be a pretty unit, rather an industrial machine. The crank will run in 1/2" ID ball bearing races, and the main frame is 10mm x 75mm mild steel held together with 5mm cap screws. The bearing housings are aluminum and I super glued them to the upright whilst I drilled and tapped the 4 fixing cap screws (also M5).

[MJM460]

A good start Robert.

It will be an interesting project.

MJM460

[Robert Hornby]

Some progress on the crankshaft, I have locktighted the webs to the shafts and I will then pin them with 3.2mm (1/8") pins. Also I have commenced the Port Block Pedestal, I am using a piece of Cast Nylon I had in my "maybe I will use it some day" box. It is an off cut from a bearing from a wire drawing machine, it is extremely tough and need no lubrication, it machines lovely. I amusing my home made rotary table for the radial slots, it is a bit crude but it does the job.

[Robert Hornby]

More work on the compressor. I intended to fix the side bearing flange to the cylinder with cap screws but having super glued them together to hold them whilst I drilled and tapped. But I was not happy that I hadn't got it in quite the correct position I had to separate them. I took a lot of work to get it to move. So I decided that just the super glue and then a fillet of J B Weld would do the job nicely.

[Robert Hornby]

Progress has been made on the compressor with only the piston and rod to make to have it close to finishing. It looks a bit like a model you would buy from IKEA 
I an hoping it will work for me so keeping fingers crossed.

[Admiral_dk]

The parts looks nice so we will as requested cross them 
and still following.

[Robert Hornby]

Well I have finished the compressor build but it is a TOTAL failure  ,
I am obviously missing something. It does pump a microscopic amount of air but nowhere enough to drive a model. The model will run on 4 psi from the compressor.
Any ideas?

Also I am trying to add as an attachment a video of it but that is not working either. (must be something to do with it being Friday 13th 2020).

[Jasonb]

Which side of the plastic block do you have against the cylinder? usually only be the side with the 4 holes in it not the linking grooves

Also are your end covers blocking the passage of air from the cylinder, in the photo of all the parts there is no notch from passage to cylinder unless you have grooved out the underside of the cover

[Robert Hornby]

Thanks Jason, There are notches in both the end covers, I even opened them up a bit as the original notches may have been a bit restrictive. I don't quite understand your first sentence.
Robert

[MJM460]

Hi Robert, that is disappointing after the work you have done so far.

Does the effort required on the handle feel like it is doing much work?  How does it vary throughout a revolution?

Assuming the porting checks prove out OK, and that you don’t have excessive leakage from the port faces,  I am wondering how much clearance volume the cylinder has at the end of the stroke.  A compressor should have as little clearance volume as possible without the piston hitting the cylinder head, so just a fraction more than necessary to allow for any slack in the crank pin and bearings.

The air in the cylinder at the end of the discharge stroke has to expand to a little below atmospheric pressure before any new air is drawn in, then re-compressed to the required discharge pressure before there can be any delivery.    This can severely limit the delivery capacity.

I am also thinking further on the issue of a discharge check valve discussed earlier in the thread.  The difference between a pump and compressor is the compressibility of the fluid.  When the discharge port of an oscillating pump opens, there is no back flow of fluid from the discharge side, so no real problem.  However with an oscillating compressor, the discharge port opens, the cylinder pressure is only inlet pressure before compression, so air flows back into the cylinder and has to be recompressed.  This will definitely affect the compressor efficiency, but perhaps not so much the capacity.  It will just make it harder to turn the handle.  Still, might be worthwhile adding the discharge check valve just to make the machine easier to turn.

MJM460

[Jasonb]

Robert these are the faces of some of my double acting wobblers, they only have an opening at the ends on an arc that matches the arc the cylinder port moves in. The connection between the pairs of holes is within the body not an open arc like you show being milled into the nylon but I don't know which way you have assembled things. Just having the holes means there is a smaller area for losses. Also make sure gap between the pairs of holes is not less than the hole in the cylinder.

From my video I would say you should not need a check valve as all I did was link the two engines with a bit of tube.

Also have you tried turning the handle both ways or moving the tube, the small engine may not run on suction

This is the green and red engine doing the pumping, also note the middle has been relieved which reduces friction and ensures the faces sit down and seal the ports.



Similar group of just the 4 holes in the form of slots on this horizontal one



And this is how I tend to notch the cylinder ends

[Zephyrin]

May I dare to ask if you are turning the crank in the right direction?

if there are no leaks, and porting correct, all the cylinder volume of air has to be found in the small engine cylinder...
if it doesn't, there are too much leaks in the air path, or too much drag in the little engine...
cranking the pump very fast, may overcome that, maybe.