Is it possible to calculate pressure at a point in a pipe, where a solenoid valve shall be placed, given that

  • the pipe carries water (utility supplied, regular water)
  • from an overhead tank (at a certain height from ground)
  • height of tank (i.e. max water column height, although not sure if vertical pipe-length should be added to it ?)
  • water is flowing purely under the effect of gravity (and atmospheric pressure)
  • value is installed at a certain height from ground
  • pipe material is PVC
  • pipe diameter is say 1.5inches.
  • $\begingroup$ Bernoulli's law will get you quite close to the actual value. $\endgroup$
    – Bernhard
    Jan 15, 2012 at 18:43
  • $\begingroup$ Thanks @Bernhard. Care to elaborate a little ? Would be an understatement to say that my high-school physics is a bit rusty. $\endgroup$
    – bdutta74
    Jan 16, 2012 at 18:45
  • $\begingroup$ The result of this is already given in the answer by Martin (without mentioning Bernoulli's law. Basically, neglecting v-terms, giving dp=g dz $\endgroup$
    – Bernhard
    Jan 18, 2012 at 8:53

1 Answer 1


If the fluid is pretty incompressible, the flow rate isn't high and the pipe is wide enough that there aren't surface effects. Then the pressure is simply the height of the head of water above the point multiplied by the density of the fluid.

eg. Water is 0.0361 lbs/cubic inch, so a head of 1ft = 12 inches = 12 * 0.0361 = 0.43 psi

  • $\begingroup$ The fluid happens to be water. Is it compressible ? Pipe is either 1" or 2/3" dia, wonder if it is "wide enough" ? Here's a picture. I wonder if the height of the head of water is the length AC, or AB ? $\endgroup$
    – bdutta74
    Jan 16, 2012 at 18:44
  • $\begingroup$ It's AC, for water in ordinary plumping then just the height is fine. $\endgroup$ Jan 16, 2012 at 19:58

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