Supersonic Control Valves

[PaoloR]

Does anyebody has experience or information about "Supersonic Control Valves"?

As far as I know, in control valve, supersonic flow must always be avoided in control valves. In techncial literature from main Manufactuers of control valves 8fisher, masoneilan, Samson, etc...) there is no reference to this type of valves.
According one of our customer, in Power Generation industry, for some applciation they are using this type of valves to control steam flow.

Any help will be appreciated.

Thanks

 

[gerhardl]

PaoloR:

http://www.iceweb.com.au/Valve/Power/HORA Steam Conditioning Valves Overview.pdf

??? (page 4)

 

[MattC1234]

Supersonic flow cannot occur in a "standard" piping configuration, the valve itself would need to act as though it were a convergent divergent nozzel in order for supersonic flow to occur and he downstream pipework would need to be expanding downstream of the valve. This can in theory occur within the valve trim, control valve manufacturers call this point "Choked" flow, in other words no further decrease of downstream pressure will allow for more flow to go through the valve.

I am not really aware of specific scenarios where a valve manufacturer would want supersonic flow to occur, especially at the outlet of the valve. Some process engineers will specify process conditions that would result (post pressure drop) in higher than sonic velocities downstream of the valve, however in reality this will not occur, the downstream pipework and system would act as a restriction to flow and there would be a pressure drop downstream of the valve or the downstream pressure would be higher. The convergent/divergent nozzel could occur if an incorrectly "sized" valve was selected to fit into an incorrectly "sized" line. By "sized i mean general valve body diameter.

 

[gerhardl]

Additional to MattC1234:

You are correct in your assumption for 'standard piping' if this is limited to normal, standard, flow processes in a closed piping system with standardized flow within certain limits. As soon as you add startup or emptying steam pipelines and vessels, gas pipelines and even water pipelines filled or emptied too fast, and valves throtteled to hard against atmosphere/low pressure, cavitation processes can occur within the valve and special valves are needed.

 

[MortenA]

I think its important to clarify your medium: Liquid, gas, steam or multiphase?

For a liquid its a good rule to avoid choking since this means that you may experience cavitation in the valve with high wear to follow, for gas, steam and MP its very common to have choked flow.

When you say "supersonic" are you refering to a regime where the normal rules for choked flow no longer apply?