Flow rate through a partially closed ball valve?

Mark Eatherton

Ball valves were not meant to be used as chokes. Especially under your circumstances. It will cause the seat to fail.

I'd recommend you look into the use of a circuit setter. THEY are designed for use in a partially closed position.

ME

Jim_158

Flow rate through a partially closed ball valve?

I am trying to determine how much water passes through a 1/2" ball valve with the handle ~30° from the closed position. Additional info: Inlet 11psi, outlet 0psi, water temp ~240°. Application: surface blow off on a 500HP boiler operating at 11psi. 1/2" Ball valve Cv=~15.5? I have searched Google, etc... and haven't found any info yet. Anybody have any input?

Brad White_185

I agree with ME

and by golly that rhymes.

Ball valves are better than nothing. Now, for surface skimming, do you mean to remove impurities? A lower velocity might be a better approach. I usually specify an F&T trap at the waterline with a good strainer- as much as an overflow or equalizer between parallel boilers as it is a surface blow-off. Just a thought.

Mark is right though. A good balancing valve (the term "circuit setter is a B&G trademark for what really is a metered 1/4 turn ball valve).

A good Macon, Tour and Andersson, Victaulic or Mepco/Oventrop multi-turn valve, all of which have integral T&P ports, is a far better approach.

Jim_158

My responsibility is to design a cooling control/heat recovery system for the discharged water. Any changes to the valves and/or converting to an automated blowdown system is for another day.
I also realize there will be about 2.9% flash from this discharge, which I assume will have some effect on the flow rate calculation, however I assume it will be relatively minor for calculating the amount of cooling required.

Brad White_185

Flash and Flow Rate

Flash steam will only effect flow rate at the point of release to atmosphere (fairly minor at that). If the pressure is maintained, no flash as you know. The water seal maintains that but will allow some vapor recovery. If you discharge below water level in a flash tank, I would not consider any flash effect on flow rate at your pressures.

[Deleted User]

Bucket and stop watch...

You'd probably need to find a metallic 5 gallon bucket, which can generally be found in restaurant settings. (pickle or lard bucket)

Place bucket below discharge pipe and use stop watch (Cell phone) to clock the time required to fill the bucket.

3600 divided by elapsed seconds, times the measurement unit (5 for 5 gallons) = gallons per hour, Divide by 60 for gallons per minute.

Any flate plate heat exchanger manufacturer should be capable of providing you with a good HXer to get 'er done.

Based on your delta T,s it won't be very large.

ME