Snifting valve

Discussion on Stirling or "hot air" engines (all types)
Aviator168
Posts: 308
Joined: Tue Feb 08, 2011 2:29 pm
Location: Brokeville, NY. USA

Snifting valve

Post by Aviator168 » Tue Dec 20, 2016 9:30 am

How come most of the stirling engines seen on the net has no balance valve at all?

Trevor
Posts: 211
Joined: Sun Nov 06, 2016 4:07 am

Re: Snifting valve

Post by Trevor » Wed Dec 21, 2016 2:09 am

HI aviator - Do they need a balance valve?
Trevor

Ian S C
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Joined: Thu Dec 02, 2010 5:15 am
Location: New Zealand

Re: Snifting valve

Post by Ian S C » Wed Dec 21, 2016 2:53 am

On a low pressure/atmospheric motor, the snifter valve is there to maintain pressure, ie to stop the pressure dropping too far bellow ambient, with a little luck a bit of positive pressure can be obtained. A simple way of doing it is to use a leather (or similar) cup valve on the piston, this works like a bike pump (it also helps if the piston is too loose). I'v tried on a number of motors with little if any effect.
Ian S C

Trevor
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Re: Snifting valve

Post by Trevor » Wed Dec 21, 2016 3:15 am

Thanks Ian - I had no idea, though wouldn't it suck air back through on the vacuum return, or do they make the hole real small?
Trevor

Aviator168
Posts: 308
Joined: Tue Feb 08, 2011 2:29 pm
Location: Brokeville, NY. USA

Re: Snifting valve

Post by Aviator168 » Wed Dec 21, 2016 4:03 am

Trevor, the purpose of the valve is to confirm the pressure in the cylinders with crank case in the beginning of each cycle, heating and cooling. Without the valve, a lot of atmospheric engines losses air that leads to lost of power.

Trevor
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Joined: Sun Nov 06, 2016 4:07 am

Re: Snifting valve

Post by Trevor » Wed Dec 21, 2016 4:23 am

Thanks Aviator - I see the light now so to speak. I wouldn't have thought that it would help small models like I am building. I would expect that it would be hard to fit onto small pistons and Ian has tried it. but not making much difference.
I might give it a go and see if it does help with one that I have that does leak through the piston. I was going to try and make a Teflon seal for it, but the valve idea might just work.
Trevor

Aviator168
Posts: 308
Joined: Tue Feb 08, 2011 2:29 pm
Location: Brokeville, NY. USA

Re: Snifting valve

Post by Aviator168 » Wed Dec 21, 2016 7:14 am

On a alpha engine. All you have to do is create a small air passage way inside the cold cylinder wall between the top of the piston and the skirt of piston when it is at half stroke. I am not sure how it is done on other types of engines.

Trevor
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Joined: Sun Nov 06, 2016 4:07 am

Re: Snifting valve

Post by Trevor » Wed Dec 21, 2016 8:05 pm

Well! That is good news. Now that would work as all the air by then has done its job and the displacer will be then falling which would cause a small amount of air into the engine. Worth a try - Thanks Aviator. Trevor

cbstirling2
Posts: 156
Joined: Sat Dec 17, 2016 9:35 pm

Re: Snifting valve

Post by cbstirling2 » Wed Dec 21, 2016 9:12 pm

Aviator: "All you have to do is create a small air passage way inside the cold cylinder wall between the top of the piston and the skirt of piston when it is at half stroke." Does something like that apply to beta and gamma engines?

Manson engine also perfected as the Manson Ross have a grove cut into the destined to allow for air to leave at top dead center and bottom dead center. I assume that effect is the same as the snifter valve? I read however the Manson engine doesn't have as much power as a traditional Stirling engine.
Thinking about the need for the valve it does makes sense as the Engines run longer and longer. Ian, you mentioned that the valves didn't make much difference. But I wonder if you graph out rpm level overtime one might see a difference?
CBStirling2

cbstirling2
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Re: Snifting valve

Post by cbstirling2 » Wed Dec 21, 2016 9:16 pm

CBStirling2

cbstirling2
Posts: 156
Joined: Sat Dec 17, 2016 9:35 pm

Re: Snifting valve

Post by cbstirling2 » Wed Dec 21, 2016 9:17 pm

Oops I meant Manson Rupp not Ross.
CBStirling2

Ian S C
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Joined: Thu Dec 02, 2010 5:15 am
Location: New Zealand

Re: Snifting valve

Post by Ian S C » Thu Dec 22, 2016 1:10 am

A friend's small (4" bore) Heinrici motor, built under licence in New Zealand. The snifter valve can be seen at the bottom of the cylinder where it joins the furnace.
Sorry about the rubbish, but Mat collects Motor Bikes, among many other things.
Ian S C
DSC01089 (640x480).jpg
DSC01089 (640x480).jpg (206.02 KiB) Viewed 7037 times

Trevor
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Re: Snifting valve

Post by Trevor » Thu Dec 22, 2016 1:21 am

Hi Ian - It looks as if this can be controlled by the valve for best performance.
Trev

Ian S C
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Location: New Zealand

Re: Snifting valve

Post by Ian S C » Fri Dec 23, 2016 2:57 am

Yes there is some control with that valve, but I have not studied it too much as yet. At first it wouldn't go, but Matt got Peter Lynn from Ashburton (about an hour south of here) to have a look at it, and they removed a modification that had been done to the bottom of the hot cap, It works quite well now. These little motors were used on water pumps, mainly on farms for household water.
Ian S C

cbstirling2
Posts: 156
Joined: Sat Dec 17, 2016 9:35 pm

Re: Snifting valve

Post by cbstirling2 » Mon Dec 26, 2016 12:04 pm

Aviator168 wrote:On a alpha engine. All you have to do is create a small air passage way inside the cold cylinder wall between the top of the piston and the skirt of piston when it is at half stroke. I am not sure how it is done on other types of engines.
Aviator168, I've been thinking about what you wrote... Why did you say at half stroke? Thinking about it, I think you would what something like that at bottom dead center.

In the attachment, I have a drawing of two designs that I drew.
stirling-snifting.png
stirling-snifting.png (51.57 KiB) Viewed 6991 times
The half-Manson on the right. The half Manson design is simply a hole drilled to release pressure at the end of the expansion phase (bottom dead center) (C). Also if the cylinder drops below atmospheric pressure air could go in words. I think the benefit of this would be to lessen the sensitivity between the size of the power piston and the displacer. (At other parts of the cycle, (D), the hole wouldn't matter)

The design on the left could be used if there's hesitation to have the expansion area completely vented to the outer atmosphere. In this case we could be a little chamber for some access pressure (A) and or excess vacuum to be equalized. I only included because I thought of it. However I think the half-Manson design would be simpler and better.

Thoughts?
CBStirling2

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