# Pneumatic Return Slave Exhaust Valve



## cfellows (Sep 4, 2011)

While I continue to noodle over the design of my steam powered vehicle with attendant boiler and motor, I decided to tackle another project on my bucket list. One of the weaknesses of my slave exhaust valve compressed air engines is the spring. It's always a struggle to find the right size and the right "springiness". Ideally, the spring should be stronger at higher speeds to return the valve faster. At idle speeds, where the input air pressure is much lower, the spring needs to be much weaker so the engine will still fire.

Early on I figured that using the input air pressure to return the slave valve between power strokes would be the ideal solution. But I never got around to designing one. Well, here it is. Since I've discovered o-rings, a whole new world has opened up to me. By the way, I see I forgot to annotate the exhaust hole in the left drawing. You can see it properly annotated in the right drawing.







On the left, the inlet valve is closed. High pressure air in front of the valve is directed around to the back of the slave valve stem. It's 1/8" diameter, rides inside two sleeves, and is sealed with an o-ring.

When the inlet valve opens, high pressure air is directed against the face of the slave valve which is 3/16" diameter. This will cause the slave valve to be pushed to the right, sealing off the exhaust hole in the side of the head and opening up the hole into the cylinder to the high pressure air.  When the inlet valve closes, the pressure behind the valve (and in front of the slave valve) will drop which will allow the higher pressure air behind the slave valve to once again close it.

Here are a few pictures of the head so far. I will be using my trusty old single cylinder vertical engine to test the prototype. I've used this engine on every new valve prototype I've built and it has served well.






The upper, smaller hole will be the high pressure passage to the back of the slave valve. The lower, larger hole will be the passage to the front of the slave valve and into the cylinder. The two holes on the outer edge will be drilled larger and tapped for set screws which will hold the inlet valve assembly in place.






Here is the back of the head. You can see the small, diagonal hole that leads up to the smaller high pressure passage leading to the air source. I can see I also need to clean this hole out. I drilled all the holes first, while the blank was still rectangular. Then I cut and ground the head to it's current shape, dunking it in water periodically to cool it off. Obviously some of the steel dust got into the passage and rusted a bit. 






Next, I'll need to build the valve assembly. Or I might borrow the assembly from my horizontal single engine since it should be the same size...

Chuck


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## kcmillin (Sep 4, 2011)

Great Design Chuck!! You have so many. Its So simple, and very little to go wrong. I am sure this will get built many times over. I know I will 

Kel


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## dvbydt (Sep 5, 2011)

That looks worth a try. The servo action should help with the speed of operation, might be an idea to use a plastic for the shuttle, it will have less inertia. Looking forward to your next post.

Ian


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## cfellows (Sep 6, 2011)

dvbydt  said:
			
		

> That looks worth a try. The servo action should help with the speed of operation, might be an idea to use a plastic for the shuttle, it will have less inertia. Looking forward to your next post.
> 
> Ian



Hadn't thought of using plastic... might be worth a try.



			
				kcmillin  said:
			
		

> Great Design Chuck!! You have so many. Its So simple, and very little to go wrong. I am sure this will get built many times over. I know I will
> 
> Kel



Thanks, Kel. I'm sure hoping it works as expected.

Here's the inlet valve assembly. Still have to bore and tap the holes which attach the cap to the bottom assembly and a few other odds and ends. I will be away from internet access for the next week. Going back to Iowa to visit my mom and she hasn't arrived in the computer age yet.  ??? Maybe someone in her apartment complex will have unsecured wireless I can tap into...

The valve is 13/16" long, the stem is 3/32" diameter and the valve head is 9/32" diameter. I'm going to try this without a spring and retainer to see if the inlet air pressure is enough to close it between power strokes.






Chuck


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## cfellows (Sep 15, 2011)

Got my pneumatic slave valve design working today. Here's the video.

[ame=http://www.youtube.com/watch?v=jMh9sdmUUl8]http://www.youtube.com/watch?v=jMh9sdmUUl8[/ame]

I'm quite pleased with the way it works.

Chuck


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## kustomkb (Sep 15, 2011)

Brilliant Chuck!!

You should be pleased. Great job.


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## kcmillin (Sep 15, 2011)

Great Job Chuck. Perfect balance throughout all speeds!

Brilliant Indeed!

Kel


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## dvbydt (Sep 16, 2011)

Super solution Chuck. You realy do show some unique solutions for these air engines.
 I have been experimenting with your ball and spring and found the same problems. If I can get my act together, I should be posting a video under my Compressed Air V8 thread showing where I have got to. 

Ian


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## lazylathe (Sep 16, 2011)

That sounds really cool Chuck!!!
Almost sounds like a gas engine.

I like the design of your single cylinder engine!
Are there any plans for it or was it something you threw together??
Almost looks like a bit of square tubing for the lower part.

Andrew


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## picclock (Sep 16, 2011)

Hi Chuck

Thanks for sharing this with such good drawings and explanations. 

I hope you can bear with me for being a bit thicker than normal (probably a senior moment), but from your drawings I cannot see how the shuttle valve opens. At the instant the inlet valve is raised, the pressure on the left hand side of the valve increases until it is equal to the pressure on the right hand side. As the pressure at both ends are equal I can't see where the pressure differential that moves the shuttle valve right is coming from ???

I hope it doesn't stop working if you don't understand it ;D

Best Regards

picclock


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## cfellows (Sep 16, 2011)

picclock  said:
			
		

> Hi Chuck
> 
> Thanks for sharing this with such good drawings and explanations.
> 
> ...



Thx, picclock. Since the diameter of the valve on the left is larger than the diameter on the right, there is a larger area for the air to push against. Pressure is measured in pounds per square inch, and the more square inches you have the greater the force. Hope that helps...



			
				lazylathe  said:
			
		

> That sounds really cool Chuck!!!
> Almost sounds like a gas engine.
> 
> I like the design of your single cylinder engine!
> ...



Thanks, Andrew. This was one of my earlier engines and is a little less elegant than some of my later models. I've used this engine for almost all of my valve prototypes, so it's seen a number of different head configurations. The crankcase is made from a piece of square tubing. The crankshaft is a built up model, using roll pins to hold it together. The flywheel is also built up from tubing and rods. The bore and stroke are both 3/4". As you can see, it runs in 2 stroke mode since the cam is fixed to the crankshaft.



			
				dvbydt  said:
			
		

> Super solution Chuck. You realy do show some unique solutions for these air engines.
> I have been experimenting with your ball and spring and found the same problems. If I can get my act together, I should be posting a video under my Compressed Air V8 thread showing where I have got to.
> 
> Ian



Thanks, Ian, looking forward to some pics and a video. I always like seeing variations that others have done with my design.

Chuck


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## BronxFigs (Sep 22, 2014)

Hello Chuck-

Believe it or not, I just found, by chance, this Pneumatic Slave-Valve"" thread and also your earlier "Prototype Ball Bearing Inlet Valve" thread.

I am  bit confused....in the above diagram, I think I understand the concept behind theis valving configuration, but the O-ring?  I'm lost.  Does your slave valve slide, left and right,  _through_ the O-ring?

Referring to your diagram: ... there looks like there is a cylinder/sleeve- (bronze green section) -through which the slave-valve slides, and a very dark-grey, unlabeled, projection at the extreme right end of the cylinder head, just adjacent to the HP air channels....is this some kind of a plug?  Both the O-ring and the sleeve(s) seem to be fixed in position.  You note that there are "sleeves"...but I think I see only one, internal, sleeve located on the right side of the head.

Any thing else that you can note to clarify the diagram....or, am I just dense?

Frank


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