Fluid velocity at valve opening for a eccentric disc valve

[processrookie1]

I'm investigating some erosional failures in cooling water piping just upstream of a temperature control valve. The TCV is an eccentric disc rotary valve, which normal operates between 10 and 20 degrees open.

I'm trying to calculate the fluid velocities just as the fluid enters the small flow area that the disc creates when it's 10 to 20 degrees open. I'm able to calculate the fluid velocity in the upstream and downstream piping, which is well within erosional limits. However, I suspect that the velocity just as the fluid enters the valve open is causing the erosion, and the erosion pattern on the failed spool piece supports this theory.

Is there a method I can use to calculate this velocity at the valve opening? The little I've read requires me to obtain proprietary info ("entrance coefficients") from the valve manufacturer, but I don't even know what I would do with it. Is anyone familiar with a method I can use to confirm my velocity is exceeding my erosional limits of the upstream material??

Thanks

 

[LittleInch]

As the area is not a fixed shape I doubt you will get a single answer as the velocity will vary over the variable cross section

This is a valve supplier question and you need to provide flow, pressure drop, temperature and fluid particulars to him to see if the valve is operating outside of its velocity limits.

Is there any particulate matter in the cooling water?

If you're only operating at a range between 10 and 20% it sounds to me like the valve is just too big and hence it is having to create high velocities in only one section.

some pictures would be nice!

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[processrookie1]

You've confirmed my suspicions. I'll go back to he vendor with more details.

No particulates to be concerned with in this scenario.

The valve is oversized based on current throughput, but resizing it isn't on the table as the capacity will be needed in the future.

I'll work on getting pictures. The TCV is a fisher model 8580 to give you an idea on what I'm working with.

 

[LittleInch]

It might be nothing, but just check it is installed the right way around. There is a flow arrow on the body somewhere.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[gerhardl]

'Corrosion' here is obviously cavitation. Even good-quality control valves can have cavitation at relatively low upstream pressures, provided the opening is small enough. I do believe that when when you get the data from the factory, that your valve is for fairly long periodes operating with an opening of only a few degrees, far lower than the expected 10 -15, possibly near 'hairline cracking'.

You might solve your problem by a smaller dimensioned bypass, or by adjusting your control to accept a larger amplitude wider temperature limits, forcing the valve to close 100% for longer periodes and opening wider when opening.

The idea of both is to avoid the cavitation and turbulence by a small crack-opening, and assure that your valve is properly shut (not hairline leaking) when closed.

Note LittleInchs' comment on correct mounting, including necessary straight stretches and isolating valves before and after for inspection, and correct adjusted end-position for closing. Actuator correctly sized for the present forces necessary for closing?