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Which valve has better flow? and a question or 2 about UHMW

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Which valve has better flow? and a question or 2 about UHMW

Unread postAuthor: ramses » Fri Nov 13, 2009 11:00 pm

I have seen two types of barrel sealing "T" piston valves, and I was wondering which would have better flow, all other things constant.

There is the standard valve where the seat is the barrel halfway into the tee, such that it appears to be in the middle of the chamber port.

there is also this style:

Image

about the UHMW, mcmaster also lists "unbreakable" oil-filled UHMW. This is significantly more expensive; is there an appreciable difference in their toughness?
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Unread postAuthor: Technician1002 » Fri Nov 13, 2009 11:47 pm

The ones that come all the way to the center of the T block half the opening from the chamber into the T. The drawing above has the barrel flow obstructed by the piston as it moves back. The best is in the middle ground where the piston retracts out of the flow path. This makes the piston shorter and with less mass, which improves speed as well as flow.

My latest valves are shorter than their diameter.
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Unread postAuthor: niglch » Sat Nov 14, 2009 1:20 am

@Technician1002: Yup definitely better that way. Probably more like it would look like with real pipe fittings since a reducing bushing screwed into a T would look a lot more like that. I wasn't paying much attention to the dimentions of everything when I drew up that sketch. I'll definitely keep it in mind if I ever do build something like it.

@ramses: I was only consdiering that design for a hybrid made of metal pipe and fittings. My assumption was that I was not machining the metal in any way (because I do not have such equipment). I'm not sure how I would get the barrel to extend into the T with metal parts.
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Unread postAuthor: Technician1002 » Sat Nov 14, 2009 1:41 am

niglch wrote:@Technician1002: Yup definitely better that way. Probably more like it would look like with real pipe fittings since a reducing bushing screwed into a T would look a lot more like that. I wasn't paying much attention to the dimentions of everything when I drew up that sketch. I'll definitely keep it in mind if I ever do build something like it.

@ramses: I was only consdiering that design for a hybrid made of metal pipe and fittings. My assumption was that I was not machining the metal in any way (because I do not have such equipment). I'm not sure how I would get the barrel to extend into the T with metal parts.


Now look at the porting and piston shape on my newest build. :twisted:
Instead of a T with a chamber feeding in one side, I have 3 ports for almost 360 degree inlet. :D
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Unread postAuthor: ramses » Sat Nov 14, 2009 11:38 am

Well I do have access to machining facilities, so a custom made part is an option. My only concern is performance. Which would be more efficient, a traditional piston valve or the one you posted the picture of, tech.

To get a metal pipe into a tee, you could imitate my piston hybrid, and use some copper fittings. Larger sizes could be accommodated with parts from mcmaster. you could get up to 1.5", although it wouldn't be cheap. you could use a standard pipe thread adapter and a reducing bushing.

but for the cost, you could probably get one machined from aluminum.

and does anyone have any experience with oil filled UHMW vs regular UHMW?
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Unread postAuthor: D_Hall » Sat Nov 14, 2009 1:18 pm

What is this UHMW you speak of? I'm familiar with UHMWPE (ultra high molecular weight polyethylene), but if you leave the PE off of that I find my self asking, "Ultra high molecular weight....what?"

Are we still talking PE or is there something else that goes by the name UHMW that I am simply unaware of?
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Unread postAuthor: Technician1002 » Sat Nov 14, 2009 1:21 pm

ramses wrote:Well I do have access to machining facilities, so a custom made part is an option. My only concern is performance. Which would be more efficient, a traditional piston valve or the one you posted the picture of, tech.


To prevent breakage (high speed parts take a beating) I prefer unibody solid block construction. To improve speed, I prefer lighter materials. An aluminum piston VS a HDPE piston of the same dimensions is over twice as heavy, thus over twice as slow.

To get a metal pipe into a tee, you could imitate my piston hybrid, and use some copper fittings. Larger sizes could be accommodated with parts from mcmaster. you could get up to 1.5", although it wouldn't be cheap. you could use a standard pipe thread adapter and a reducing bushing.


The valve body and chamber can be built in many configurations and out of many materials.

but for the cost, you could probably get one machined from aluminum.

and does anyone have any experience with oil filled UHMW vs regular UHMW?


I have not tried the oil filled stuff. I have used both UHMW and HDPE. The UHMW is harder to machine. It tends to create long strong threads when cut that are like fishing line and don't want to cut off your piece. HDPE turns curls much like machining iron or aluminium. This makes it easy to turn nice smooth surfaces. Getting a smooth turned finish on UHMW is an exercise in futility. Compare my Mouse Musket Piston to the 2.5 inch QDV piston for examples of the difference in the surface finish after turning.

As for the finished product, I think the UHMW is tougher than HDPE and will take more abuse as a piston.
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Unread postAuthor: dewey-1 » Sat Nov 14, 2009 1:42 pm

Here is a link I find quite useful for information and specifications for "plastics".

http://www.ides.com/generics/

I think most people have a tendency to drop the PE from UHMW.

Here is oil filled UHMW;

http://www.totalplastics.com/products/413
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Unread postAuthor: Moonbogg » Sat Nov 14, 2009 2:57 pm

Well its real fun to include the PE at the end of UHMW, that way you can impress people with your knowledge that there are two more letters at the end even though they are never used.
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Unread postAuthor: D_Hall » Sat Nov 14, 2009 5:05 pm

Sorry if you take offense, Moon. In my world, the PE is used. Without them, I wasn't 100% sure as to what we're discussing. Ultra high molecular weight polystyrene?

Personal experience with UHMW (there, no PE, just for you Moon): Very tough. Reasonably high melting point compared to other PEs (to be expected). Self lubricating so should be excellent for usage in things like single-piece piston designs if you can get a good surface on it (it melts without molecular damage so that's an area to look into. Great for use in body armor in a fiber form (see: Spectra).
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Unread postAuthor: jimmy101 » Sat Nov 14, 2009 10:10 pm

UHMW is also used for things like starches and other biopolymers (DNA, RNA, polypeptides ...) and some synthetic lubricants.

But by far the most common meaning is UHMWPE.

Still, it's always best to use the most complete name possible. Especially in a field like spudding where people pull in parts and supplies from all over the place.

A plumber knows what a "street elbow" is. A plastic expert knows what PE means. A rifle expert knows what a "muzzle brake" is. An electronics wonk knows what a 555 is. A digital controls expert knows what a PLA is. A robotics geek know the difference between a DC motor, a servo and a stepper. A cook know all his starchy veggies ...

A spud isn't always spud, it depends on the context. Spud has a different meaning to a cook, a plumber, a wrestler, ...

Besides, the plastic people are some of the worst when it comes to a unified and consistently used nomenclature. Many commonly used plastics have several names, many of which are nearly useless for actually figuring out what is being referred to.
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Unread postAuthor: Technician1002 » Sun Nov 15, 2009 1:09 am

jimmy101 wrote:UHMW is also used for things like starches and other biopolymers (DNA, RNA, polypeptides ...) and some synthetic lubricants.

But by far the most common meaning is UHMWPE.

Still, it's always best to use the most complete name possible. Especially in a field like spudding where people pull in parts and supplies from all over the place.

A plumber knows what a "street elbow" is. A plastic expert knows what PE means. A rifle expert knows what a "muzzle brake" is. An electronics wonk knows what a 555 is. A digital controls expert knows what a PLA is. A robotics geek know the difference between a DC motor, a servo and a stepper. A cook know all his starchy veggies ...

A spud isn't always spud, it depends on the context. Spud has a different meaning to a cook, a plumber, a wrestler, ...

Besides, the plastic people are some of the worst when it comes to a unified and consistently used nomenclature. Many commonly used plastics have several names, many of which are nearly useless for actually figuring out what is being referred to.


Jimmy, I'm impressed at your breadth of knowledge to put that post together. The only one I am not familiar with is the spud in relation to a wrestler. I was able to follow all of the rest of the items. FYI, a 555 is the first IC I worked with. :D A 4046 is my favorite. Linear VCO, phase detector, all rolled into one nice neat package. :D Low power CMOS.
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Unread postAuthor: john bunsenburner » Sun Nov 15, 2009 5:13 am

Talking of plastics, (and seeing as how this has thread is a little off topic already) and the nomenclature of plastics.

I have two rounds stocks of "supralen" in my garage and would like to know what this is/ what its characteristics are like. I was told it is similar to PE, its white, similar to nylon(color wise that is), and has the tendency to deform during storage, but can be bent back into shape( 25mm and 20mm round stocks do this, no clue about thicker pieces).

Any ideas?
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Unread postAuthor: Gippeto » Sun Nov 15, 2009 11:22 am

Tried google?? I think not..it was right at the top. :roll:

http://www.atlasortho.com/sub%20Product ... en500.html

Supralen is one of the easiest to work plastics available. Extremely user friendly. Made of a high molecular weight, high density polyethylene. Adjusting plastic is as simple as reheating in oven or with heat gun.
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Unread postAuthor: john bunsenburner » Mon Nov 16, 2009 1:54 pm

:oops:

Well thanks, looks like i picked up some good stuff there!
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