setting of balancing valve

The purpose of having a number of diameters both up- and down-stream is to enable the velocity profile across the pipe to normalise following any fitting in the pipe that would disturb it. Take a 90deg bend for example. The flow around the outside of the bend will travel faster than the flow at the inside. Several pipe diameters are needed following the bend for the velocity profile to rearrange itself to allow the effect of the bend to dissipate.

Valves are not significantly affected by the velocity profile as they introduce disturbances themselves, and are adjustable for position. However any instrument that needs a signal from the pipe that would be affected by the local velocity profile, and there are many that fall into this category, will be affected significantly if due allowance is not taken for the effects of disturbance either side of fittings.

It would be helpful to know the nature of the instrument involved in order to be able to suggest alternatives that might not be affected so much by velocity profile disturbance.

The reading will be affected by the turbulence created by having fitting close to the point of measurement and it really depends on the level of acuracy you require.

If you do need to be sure of the correct flow you might want to consider hiring an Ultra-Sound meter that does not require intrusion into the pipe. You still need to have this in a long section of pipe to reduce the turbulence but it can be anywhere along that pipe. With this you can still use the balancing valve to regulate the flow.

Good Luck..!

I have a related question, I was driving along an interstate highway and saw a pipeline running beside the highway, every so often there were 4 90 deg bends in the pipe line, like a U- shape where the pipe divered what ever was in the pipe around the U and then sent it on it's way. What is the propose of the bends?

The changes of direction are expansion loops. These are fitted into long straight lengths to allow expansion and contraction in a controlled manner.

Expansion loop I suppose.

The changes of direction are expansion loops. These are fitted into long straight lengths to allow expansion and contraction in a controlled manner.

if the installation doesnt have enough space .

Take a copper pipe for sensing for the length 2D/5D roll it up and tap the other end

(Like the ring-type/ U-bend sipon on a pressure gauge ) for, it is the length that matters.