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Flow Meters: What is the appropriate length of reducer and expander?

Q: I have to install a flow meter size 900mm on a 1,600mm water pipe line. Gravity flow with 5,600 cubic meters/hr flow rate. What will be the effect on the flow profile? Line pressure? What will be the pressure drop? Will it affect/resist flow? Meter length would be around 500mm. Please suggest appropriate length of reducer and expander.

A:

Flow rate – 5,600 cubic meters/hour = 24,656 gallons/minute
Meter Size - 900 mm = 35.43 inches
Pipe Size – 1,600 mm = approx. 63 inches
Meter Length - 500 mm = 19.7 inches
 
What kind of meter is being used? Choices – 36-inch magnetic that is about 20 inches long in a 63-inch pipe?
If it is a magnetic meter and there is gravity flow, my concern would be that the pipe must be kept full (no air in top of the pipe).
If it is a magnetic meter, straight runs and velocity profiles are of little concerns.
My data goes up to about 20,000 gpm in 24-inch pipe.
If it is a magnetic meter, ask the manufacturer about pressure drops, etc.
If it isn't a magnetic meter, what is it and then ask the manufacturer.

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