Author Topic: Control Valve  (Read 862 times)

Offline Cp489

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Re: Control Valve
« Reply #15 on: February 09, 2020, 03:10:55 PM »
Perfected the control valve. At least in my opinion. Here is some pictures of the two valve designs, thanks to your help guys.

I added pins that would help keep the lever in place. A tac-weld or two will be needed inside the valve block in order to keep the valve in the correct position.

What do you all think? Any other things I can improve on this?

Thanks again

Offline awake

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Re: Control Valve
« Reply #16 on: February 09, 2020, 03:19:42 PM »
What are you planning to tack weld? I have to say that any sort of welding AFTER machining a close-fitting system seems fraught with danger - but maybe that's just my ham-fisted welding abilities!
Andy

Offline cnr6400

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Re: Control Valve
« Reply #17 on: February 09, 2020, 03:45:47 PM »
Hi Cp489 Are you planning to lap in the plug valve in the body to achieve sealing? If so I would not do any welding afterward, or the parts will distort and probably leak. If the part on the back of the plug is a cap to retain it, why couldn't it be attached with a couple of screws to the plug body? Two screws because they won't loosen with valve rotation like a single screw at centre of cap might.

If you use spring plungers to act as detents for the operating lever, be sure to make the mount hole a through hole so you can adjust the ball end's position against the lever easily. you will likely need to. There will be a VERY narrow window of position where the lever just holds vs lever can not be moved.

If the spring plunger was mounted in the body and acted against shallow drill dimples in the plug diameter at the front or rear away from the ports, the action would be a lot smoother and more likely to stay adjusted as the plug to body fit is likely the highest precision fit in the whole assembly.

Have a look at the link below for some info on the design of spring plungers and angled dimples and holes. Vlier make very good spring plungers.

https://www.vlier.com/product_index/sld/sel_06_diam.html


Offline Cp489

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Re: Control Valve
« Reply #18 on: February 09, 2020, 03:47:27 PM »
Awake,

I am planning to make something that will stop the valve from  going past certain points. What would stop the valve from going past the dotted line?

Would the air inlet not allow for the valve to go past this point? May be a dumb question/idea.

Offline Cp489

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Re: Control Valve
« Reply #19 on: February 09, 2020, 04:03:41 PM »
cnr6400,

Yes, lapping would be an option and is what is mind now. The cap is sealing to the valve, not the valve body. I agree with you and achieving a better seal by screwing it to the valve body itself. I will change that. I will also try to find a different alternative than a tack-weld . Unless the air flow itself will keep it in the desired position.

I understand the fine line between too much and not enough when it comes to the ball sticking out of the valve block. I will research this and see visit the hyperlink you posted. Thank you so much.

I honesty didn't even know they were called "spring plungers". At least I'm learning!

Offline cnr6400

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Re: Control Valve
« Reply #20 on: February 09, 2020, 05:58:27 PM »
Hi Cp489, In plug valves, the seal is made only on the cylindrical parts with the ports cut in them. The end flange on the plug and the back end cap do not need to seal if the plug valve fit is good, and well greased.

You could also control the angle of movement by relieving part of the plug flange outside diameter or the rear cap outside diameter and putting a simple peg in the body to allow the plug valve and cap to move until either end of the relief cut hits the peg. This would save you buying spring plungers and spending time adjusting them. Jpeg is attached showing this idea.

This idea will not provide any force to hold the lever / valve at a particular angle though, if the plug friction is not sufficient to hold it, or the operating rod has two pins around the lever so it can't move. (or a curve fork set as many early engines had). Having the operating rod fully control the valve operating lever position rather than using detents or peg / cut on valve will allow adjusting valve events more precisely, giving better engine timing and higher efficiency.

There are usually many ways to do any mechanical job.  :cheers:
« Last Edit: February 09, 2020, 06:04:03 PM by cnr6400 »

Offline MJM460

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Re: Control Valve
« Reply #21 on: February 10, 2020, 08:54:49 AM »
I suspect there will always be enough friction to prevent the plug from travelling further than intended.  The steam pressure and exhaust pressure are always creating a pressure difference in the same direction, thus holding the plug against one side of the housing.  The cylinder end connections to the valve reverse twice each revolution of the engine so probably tend to bump the plug up and down a bit, depending on how much clearance there is, which might be beneficial in preventing the plug sticking.  A nicely lapped in plug will not have much clearance.

If you do put motion limiting pegs or detents of any kind, it will be important to not over constrain the motion, as the little trip levers which operate the valve have a specific geometry and stroke.  It will be worth laying out and investigating their motion before worrying about limiting the plug motion.

I suspect that Watt would have started simple, and only added complication where it was proven necessary.

MJM460

The more I learn, the more I find that I still have to learn!