HMEM EZ Engine - second engine - what sort of rpm should I get ?

[BillWood]

Hello,

Finished my second engine - HMEM EZ engine - many thanks to those who made and posted the plans. I enjoyed seeing how the piston slide valve worked

My RPM measuring device got a bit confused and gave erratic readings so I made a circle of black paper with a white stripe on it, taped it to the flywheel and that gave stable readings.

It reckons 600 rpm ......... ummmmm thats 10x per second .....doesn't seem right to me ..... does that sound reasonable or could the gadget be reading too fast ? If that sounds right maybe I could have another go and try to be a bit more tidy with everything could I crack 1000 rpm ?

Bill

 

[aka9950202]

You will need a larger compressor to get higher speed. I tried a similar setup and had the same results.

I was able to get 50rpm using an aquarium pump.

Cheers,
Andrew in Melbourne

 

[Cogsy]

For a steam/air engine, low RPM at low pressure is the sign of a well built engine, not screamingly fast operation. If you build it well enough you could probably get it to run on breath power alone.

 

[BillWood]

Thanks for the replies,

Yes, I can run it on breath power, nowhere near as fast as the tyre inflator though.

So will have another go and see if I can do better. Maybe I can tweak the sliding fit of the piston and the valve and try breath test again on this one.

Any guidelines for what size does an engine have to be before the breath test is no longer applicable ?

Will try aquarium pump and manual bicycle pump as well.

Bill

 

[aka9950202]

BillWood,

I don't know what size the engine must be fore breath power is not enough. Good question and I hope there is an answer.

Cheers,
Andrew in Melbourne

 

[rodw]

Um, I can answer that. They should be able to turn nicely at idle on just 1-4 psi. I took mine to work and hooked it up to 80 psi and it managed 16000 rpm briefly before it fell apart! so your lofty goal of 1000 rpm should be easy!

The plans for this engine was the reason I joined this forum....... I wanted metric plans as I don't do imperial units any more!

 

[JC54]

Just a quick comment, I have exactly the same rev counter and found it so unreliable retired it to the "will be useful sometime box". Now use one I built and calibrated with an industrial one. JC

 

[BillWood]

Thanks for the comments.

With respect to PSI and breathpower ; Internet searches yield various estimates that human lung capability is approx 2psi above ambient air pressure, must admit I found that a bit confusing and currently in my head I just think of human lung power as being approx 2 psi. I guess if I buy some sort of air pressure gauge from 0-10 psi one could measure breathpower. Will try and find one.

With respect to the RPM counter - I have tested this on my lathe, milling machine and bandsaw, it gives readings very close to what the lathe and milling machine claim to be capable of (Hercus 9" and Rong Fu 30 Mill) so I trust it up to 2100rpm (Mill). I did have to make pieces of black paper - black electrical tape would do - and then use a white stripe on the black background to give a good contrast so that I could get consistent readings - If I don't do that the counter gives highly variable readings - I think this is caused by nicks and scratches and variations in reflectivity in the material being tested.

My first wobbler takes much more effort for me to "blow " than the HMEM EZ - am guessing that is caused by the relatively large surface areas in contact and the retaining spring pulling those two surfaces together (F=u * N), whereas the pistons in the EZ engine are nice easy sliding fits with no spring forcing them together.

Bill