Pipe rupture drain rate for air valve 1

[swazimatt]

I am trying to size air valves on a wastewater rising main and i have come across a formula to determine the rate a pipe will drain under full rupture conditions. The formula appears to be from a vent-o-mat related source (or a very biased author) but i printed it out years ago because i knew it would be useful in the future.
The formula is:
rate of flow in l/s = 0.26.S.D
S being the slope of the pipe as a decimal
and
D is the diameter in cm

Can anyone identify this formula or have a source to calculate the draining rate of a pipe?

 

[gerhardl]

Hi swazimatt,

If you start at te other end, you want to dimension your air inlet valve to have an inlet air speed (well) below supersonic speed. Say roughly 20-40 m/s, which is the 'normal' dimensioned speed of gas in a pipeline. Very roghly you can calculate this with size of inlet and speed without bothering physical conditions.

For the liquid side draining speed would be influnced mainly by pipeline dimension, pressure at the rupture (= pipeline internal pressure), size of rupture, and outside pressure against the rupture (free air or underground or other) as main factors.

I do not believe your formula to give a correct result under anything than given, limited data and conditions for above parameters of a pipeline.

If we asume your wastewater main has conditons as a filled pipeline, normal speed will normally be, say, up to 2 m/s. I would have tried to calculate nessesary inlet of air based on a water speed out of 2-4 times the normal flowspeed at breakdown.

How does this result rhyme with your formula, and the actual conditions of 'full rupture' in the field?