Fit a 4in valve, and wind the handle down until 60m3/h is achieved. Then, take the handle off.

"Simples!ξ"

Why are you re-posting the same question you had answered a month ago?

http://cr4.globalspec.com/thread/77129

the sizing is different but also need the calculation to do it in future. the one in coulson and richardson vol 1 is hard to get your head around (or mine any way).

and the software that was mentioned i cannot seem to download.

Yep. Why not do it the hard way?

http://www.mcnallyinstitute.com/13-html/13-12.htm

First off, you MUST know the flow rate in the pipe with no orifice. Without this, there is no way of finding what size orifice will reduce the flow rate to the desired 60 m³/h.

What do P1 and P2 represent - the upstream and downstream tap pressures? Were these measured? If so, what size orifice plate was in place at the time?

Thanks, But as the coolin water branches off to many other vessels the flow rate cannot be seen, there are no bleed points either so i an do it manually with a stop watch.

P1 is the pressure before orifice plate and p2 after. i have another orifice in a different part of the plant which i calculated but was wrong because of the actual flow. so reduced it by half but still getting twice as much flow. did not want to go any lower as there is a 1inch orifice in a 6 inch line.

I am thinking of getting an ultrasonic flow meter in to see what we get but even they have a 10 percent or so error. depending on available straight length of pipe.

I'm not sure how you're calculating orifice size, but for simplicity to get an close approximation, use the standard orifce flow equation:

Q = Cd x A x SQRT((P2-P1)/density))

When I do this for the values given, I get an orifice diameter of 73.5 mm to flow 60 m3/hr

Thanks, this does sound way to big though on a 4 inch line., i would have expected it to be less than 50mm, but will have a look.