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It seems strange to me that ball valves are ball-shaped, when I would have thought a rotating cylinder with a transverse hole cut in the same way would be easier and cheaper to machine. Does anyone have any ideas?

closed as off-topic by isherwood, Ben Welborn, Tester101 Jul 20 '16 at 13:59

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    This might be a question for the engineers that designed it, rather than a do-it-yourself home improvement community. – Tester101 Jul 13 '16 at 13:20
  • I'd venture a guess that it has more to do with economy of manufacturing as well as the total length of edges/perimeter that must be sealed. – BrownRedHawk Jul 13 '16 at 17:33
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Stopcocks use a cylindrical axle.

Ball valves use less metal and are more reliable because the seal is a simple circle, whereas in a stopcock an entire surface has to mate.

As far as machining is concerned, it is cheaper to make a ball than to make a cylinder of the same diameter and the same finish grade.

  • " the seal is a simple circle, whereas in a stopcock an entire surface has to mate" That's what I was looking for. Thank you. I am surprised that you say it's cheaper to machine a ball than a cylinder – Borodin Jul 14 '16 at 22:30
  • @Borodin Why do you think ball bearings are much more common than roller bearings? It is because it is cheaper to make spheres than cylinders. – Tyler Durden Jul 14 '16 at 23:32
  • I'm not denying that it's true, it just seems very unintuitive – Borodin Jul 14 '16 at 23:35
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A sphere allows for sealing with simple o-rings in a flat configuration. This simplifies design, component acquisition, assembly, and repair and maintenance.

  • I agree all the large ball valves I work on are ball's, Less material & easy to work on and replace seals. + – Ed Beal Jul 13 '16 at 13:08
  • Please would you exaplin what you mean by "in a flat configuration" – Borodin Jul 14 '16 at 22:29
  • Not bent. Not wrapped around a cylinder wall like a potato chip. See the orange seal in this image: globalspec.com/ImageRepository/LearnMore/20121/… – isherwood Jul 15 '16 at 13:31
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Not to be disagreeable, but the idea of calling a spherical valve a "ball valve" seems logical to me. To call a cylindrical valve a "ball" valve would be... more strange.

Actually, the term "ball valve" is distinguished as a kind of stopcock (that uses a sperical valve). But "stopcock" includes ball valves or the cylindrical kind of valve that you described. Stopcock is defined (by google) as: an externally operated valve regulating the flow of a liquid or gas through a pipe.

Cylindrical valves are the kind of valve that most faucets actually use (fancy cylinders are called cartidges or stem valves); but because ball valves are so popular (I guess), valves which are called "stopcocks" or "stop valves" tend to refer to the simplest cylindrical (or conical) valve; and less often does the term stopcock refer to a ball or stem valve. If you search for stopcocks online, you will probably find many cylindrical or conical valves which are used in chemistry apparatuses- especially because they are easier to disassemble and clean and they can be less prone to chemical and thermal damage.

But again, technically, a stopcock is a broader term which basically includes any valve, typically operated by hand.

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    @Tester101 Q: Why are ball valves spherical instead of cylindrical?...strange that ball valves are ball-shaped... a rotating cylinder... would be easier and cheaper to machine... ideas? A: Cylinders are common. They are oft called stopcocks in chemistry and fancy ones are called cartidges or stem valves. Ball valve is a logical name for a spherical valve. – Ben Welborn Jul 13 '16 at 13:55
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    Note: In UK plumbing, a stopcock usually means the main valve supplying cold water at pressure into a house. The other valves in a house typically have different names according to purpose (service valve, isolation valve, check valve, float valve, pump valve) or construction (gate valve, ball valve). – RedGrittyBrick Jul 13 '16 at 14:14

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