Author Topic: Simplified Balanced Valve (Read 116061 times))

rsterne · « **Reply #140 on:** January 02, 2019, 05:19:08 PM »

Thanks for that, Brian.... Unfortunately, I don't understand how it works....

Bob

shorty · « **Reply #141 on:** January 02, 2019, 05:22:38 PM »

Brian,
Tell us more about it.

Was it hard to seal? Did it have a declining shot string? How low of a pressure before it would just knock open and stay open?

All those kinds of questions.

Brian W Cook · « **Reply #142 on:** January 02, 2019, 05:30:31 PM »

Like most of the valves posted lately .
I finally found a file reducer for my pics .

lloyd-ss · « **Reply #143 on:** January 02, 2019, 05:36:57 PM »

Quote from: Brian W Cook on January 02, 2019, 05:30:31 PM

Like most of the valves posted lately .
..........................

Your valve is from 17 years ago. Just goes to show how hard it is to come up with an idea that REALLY is new. Nice work, Brian!
Lloyd

shorty · « **Reply #144 on:** January 02, 2019, 05:37:48 PM »

Brian,
That looks nearly exactly like the simplified valve Bob is proposing.

I know you said it was 17 years ago but, we all have to know how the valve performed. Most importantly, did it have a declining shot string and were you able to tune it for a large range of power with hammer strike.

rsterne · « **Reply #145 on:** January 02, 2019, 06:53:59 PM »

Yep, it looks very similar to the valve I just suggested in this thread.... It is not surprising that the idea has been tried before in PCPs.... just long before I got back into airguns.... Pretty much every kind of valve around was invented decades (if not centuries) ago....

I am also very interested in how it performed, and how you were able to tune the shot string.... although I realize that most Big Bore guys tune for maximum power on the first shot and live with the velocity declining after that.... Were you able to tune it for a bell-curve.... or did you even bother?.... I really appreciate you taking the time to share the photos.... and any other information you can remember....

Bob

oldpro · « **Reply #146 on:** January 02, 2019, 06:58:27 PM »

Quote from: Brian W Cook on January 02, 2019, 05:30:31 PM

Like most of the valves posted lately .
I finally found a file reducer for my pics .

17 Years ago!!! Wow thats a shocker... Could you tell us the diameters of the two sections of the poppet (large end over seat and small end with Oring) Did it work ok and were you able to tune it at all via hammer strike? Also what is the stem diameter?

rsterne · « **Reply #147 on:** January 02, 2019, 07:09:07 PM »

I was curious about that as well, Travis.... but scaling from the photos tells us that the balance chamber is twice the stem diameter (28mm and 14mm on my screen).... and the seat (which is tapered) is roughly 1.2 - 1.4 times the diameter of the balance chamber (33-40mm depending on where on the taper it seals)….That would make the balance chamber diameter between 70-85% of the seat diameter....

Bob

oldpro · « **Reply #148 on:** January 02, 2019, 07:09:58 PM »

Here are some measurements from Dons valve and as you can see the ratios are about what I’m suggesting.

PakProtector · « **Reply #149 on:** January 02, 2019, 07:26:10 PM »

Thanks for the PIX there Travis...just gave me an idear on keeping the balance chamber pressurized to lower risk of hammer bounce. Put the stem port just inside the body's stem bearing when it is closed. Kick it open, and flow to the balance chamber can happen, once it is closed, it will bleed rather more slowly through the stem/body bearing clearance. Thanks!
cheers,
Douglas

rsterne · « **Reply #150 on:** January 02, 2019, 07:30:51 PM »

Douglas, the vent hole in the Cothran valve is inside the exhaust port when the valve is closed, not back inside the valve body guide hole.... at least from my recollection.... I'm sure Travis can confirm, one way or the other.... Don uses a "leaky check valve" arrangement inside the very large diameter (0.175") stem, to maintain pressure inside the balance chamber and help prevent hammer bounce....

http://www.cothranmachine.com/PowerHouse%20Valve%20from%20October%202013.pdf

Looks like you can see the vent centered in the exhaust port with the valve closed in that photo.... Also note that the valve seat is much smaller than the OD of the flange on the poppet where Travis is measuring it.... you can see the indentation on the seat washer....

Bob

oldpro · « **Reply #151 on:** January 02, 2019, 07:56:15 PM »

We can look at it another way also there are two areas of the SS valve the small end and large end of the poppets the small being .285 and large .352 that gives us .03352 square inches of area holding the valve closed or roughly a rod with a diameter of .206

PakProtector · « **Reply #152 on:** January 02, 2019, 07:57:53 PM »

Absolutely Bob, I did see that as you described...

but that is what I was staring at when I came up wid it...LOL

In any case, I am going to get me a sack of wee drill bits and some stem material and likely have a go.
cheers,
Douglas

Brian W Cook · « **Reply #153 on:** January 02, 2019, 08:00:46 PM »

The port on mine is around .550 tapering to .375 going up into the barrel . The piston is .375 . It was a pain to getting it to seat filling from empty. I have a really long string of shots recorded somewhere that ended in the last shot only going 150 fps . Using .452 rb. I’ll track that down

mann · « **Reply #154 on:** January 02, 2019, 08:15:06 PM »

Drilling threw the peek was harder to do than the stem . By putting the vent back into the body you could control the rate it exhausts the pressure off

oldpro · « **Reply #155 on:** January 02, 2019, 08:40:03 PM »

Quote from: Brian W Cook on January 02, 2019, 08:00:46 PM

The port on mine is around .550 tapering to .375 going up into the barrel . The piston is .375 . It was a pain to getting it to seat filling from empty. I have a really long string of shots recorded somewhere that ended in the last shot only going 150 fps . Using .452 rb. I’ll track that down

Thank You Brian!

rsterne · « **Reply #156 on:** January 02, 2019, 08:43:31 PM »

You lost me, Travis.... The SS Valve has two areas pushing the poppet towards the seat (0.285" and 0.352" on your valve), plus one area pushing it away from the seat (0.375")…. When the valve is closed that gives the following....

( (0.285 x 0.285) + (0.352 x 0.352) - (0.374 x 0.375) ) x PI/4 = 0.0506 sq.in.... just a whisker bigger area than a 1/4" rod.... The cracking force is therefore reduced to 52% of what it a conventional valve with a 0.352" seat would take (area = 0.0973 sq.in)....

Brian, thanks for the dimensions.... Is it the seat that measures 0.550" at the sealing diameter, or is that the exhaust port diameter?.... Did you have a spring inside the balance chamber to aid in initial sealing?....

Bob

jackssmirkingrevenge · « **Reply #157 on:** January 03, 2019, 09:47:46 AM »

Quote from: lloyd-ss on January 02, 2019, 05:36:57 PM

Your valve is from 17 years ago. Just goes to show how hard it is to come up with an idea that REALLY is new.

I know that feeling, spent years trying to perfect a pop-off type valve for an automatic airgun only to find out it was patented in 1927...

Brian W Cook · « **Reply #158 on:** January 03, 2019, 12:02:22 PM »

I checked the valve out a bit . The poppet OD is .550 and the port is close to .500 . I tapered that to the .375 going to the barrel . The return spring was 250 OD .030 wire.
It is “sticky” as built .
I used a less than slick bronze bushing for the piston to operate in because it was handy.
To do it again i would use reservoir tubing with a larger inside diameter to inhance the air flow around the valve and use a slick material for the cylinder.

Brian W Cook · « **Reply #159 on:** January 03, 2019, 12:33:53 PM »

I dug my one and only shot string out of my tool box .
This started out at 3000 psi using close to 21 ci of air . I think the 746 FPS first shot can be blamed on sticktion

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Simplified Balanced Valve

Author Topic: Simplified Balanced Valve (Read 116061 times))