# Static pressure in round pipe bends do what?

1. Jul 20, 2009

### physical1

In the controversial and well misunderstood Bourdon gauge phenomenon, I found by experiments that a flat or oval shaped bourdon tube will increase in volume significantly as the tube straightens. I filled the gauge tube with water and moved the tube with my hands. As I straightened the tube, more water flowed in due to an increase in volume of the more straight tube. Rounder pipes naturally are more efficient in storing more volume than a flat pipe, similar to how a sphere is more efficient than a rectangle. This is important because not one book or physics website that I could find truly explained the bourdon effect properly. The important fact that they all miss is that it's a significant volume change that causes the Bourdon tube to work. Most books or websites try to explain the bourdon effect by some voodoo force imbalance surface area magic - when in fact what is most important to understand is that the bourdon tube blows up and increases in volume like a balloon would, and this just so happens to cause the tube to move similar to how a balloon would move outward if pressure was applied inside. A Bourdon tube is just a special bent balloon: it would help people understand the effect more if they explained it as such.

Now I question how static pressure affects pipe bends in round cross section tubes, not flat or oval bourdon ones? Unfortunately a lot of the literature I have read is only about flow and how dynamic pressure affects round cross section pipe bends. I want to know what happens when static pressure is applied to a pipe that has a bend with a circular cross section, not an oval or flat one. Does the pipe have a force imbalance and does it buckle under static pressure if the pipe is not mounted securely, or does the pipe do some other action? Or does the pipe do nothing at all since there is a net force of zero? Does the pipe become stiffer, elongate, or unbend due to another non-bourdon effect such as stiffening?

http://www.engineeringtoolbox.com/forces-pipe-bends-d_968.html

The website calculator above implies that static pressure does affect circular cross section pipe bends, and therefore it implies a force greater than zero exists on bends. However I am not sure if this is only when the water is flowing when both a static pressure in addition to dynamic exist. It doesn't make it clear whether a purely static pressure without any dynamic flow, will cause a net imbalance on a bend.

Last edited: Jul 20, 2009