Water speed

[MasterPlumbersKeymaster]

Why should water speed in pipes be limited to some magic value?
Is the maximum speed chosen to give a Reynolds number in the transition region, just before turbulent flow begins?

[Harold KestenholzParticipant]

Water speeds in tubing are generally limited to 5-7 fps, as turbulence at obstructions will wear metal at these speeds and higher at accelerated rates. 2 fps is required to carry bubbles downward pipes. Speeds below 1 fps can create laminar flow in water heat exchangers and limit heat transfer. Not much magic – just experimental findings.

[GuestParticipant]

John:Water velocity is not limited
by any agency to my knowledge.If you wish to accelerate water to cyclotron speed you may experience some magic. Consider the following.
Where E is the energy required to propel 1 lb. of water (distilled)
through a known orifice at 40 degrees F., and e is the constant.
By using the variable”T” vector
curve criteria used for viscosity harmonics, it will be noted that an inverse proportion of the energy (E) was disapated at the junction of (e T)
This postulation is based on the conversion of water at a highly excited molecular level to steam. At this change of state of liquid to gas latent heat calculations will trigger unstable gas to reach critical mass.
Studies at MIT on cold fusion have concluded that this may one day soon be the fuel of our future.
Akmed UAR Engr.

Hearfield wrote on 20 November 2000 at 01:49 PM:
Why should water speed in pipes be limited to some magic value?
Is the maximum speed chosen to give a Reynolds number in the transition region, just before turbulent flow begins?

[GuestParticipant]

There are many reason why the “speed” of water is set at certain ranges. One often overlooked fact is that there is a critical speed, and this varies with pipe size, that water will create an aspriation effect which has may pitfalls in water distribution systems.
I can elaborate further, but it is kind of boring and not all the glamore you see in the movies or on TV.

[fourth yearParticipant]

Ahkmed:
Are you using the formula E= mcc? If so then the point of critical mass is also the point where flow velocity would be immaterial since the neighborhood would also be experiencing a velocity problem.

[SylvanLMPParticipant]

Harold, according the CDA water above 180 degrees should not have a velocity greater than 2 FPS as any higher can cause corrosion.

The problem with just figuring velocity and not the pH factor is why so many piping failures do occur.

Another point about “velocity” is the scouring action required on waste and soil lines as opposed to just storm piping.

Do you have any idea of the “velocity” of steam FLYING through a 6″ steam line with only 140 PSI behind it?

There are a whole big bunch of factors to consider BESIDES Hazen- Williams formula’s.

Material selection plays a very important part in the selection of design pressure and area Or Fixture units to be drained.
There is no one size fit all application even if you are using the same materials.

[Harold KestenholzParticipant]

Sylvan, to be technically correct, lower speeds are recommended to limit erosion. Any water speed will create erosion. Gases and minerals in the water will create corrosion. High speeds will create unacceptable erosion and corrosion. 2 FPS or less is recommended for water over 180F, as turbulence creates cavitation as the water changes to steam in the pressure drop after the obstacle and then collapses after the local low pressure zone.

For ordinary domestic water temperatures below 140F the fps can be higher, but no higher than 5-7 fps; at those speeds, the protection of laminar flow is eliminated even in the straight sections of tubing – producing noise and increased wear from the friction of entrained solids and exposure to gaseous corrosion.

2 fps is exceeded in a 1/2-inch shower stem as a shower head can deliver 2.25 gpm and 2 fps in a 1/2-inch pipe delivers 1.89 gpm, so the 1/2-inch pipe will exceed 2 fps in ordinary shower piping.

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