limits of velocity and pressure losses across valves

[engahmedbahgat]

good morning, I need some one to clarify following point for me:

1- is there is a limit value for the velocity inside the valve? , and is that limit vary from valve type to another according to valve construction and design?

2- I read about sonic speed inside the valve or regulator which occurs when inlet pressure / outlet pressure become more than about 1.89, is this velocity is a maximum limit for the velocity or what?

3- I know about the procedures and methods that used to calculate pressure losses across the valve, but I need to know, is there a maximum limit permissible for pressure loss across the valve? and is that limit depend on valve type and internal design? or permissible pressure loss depend on process conditions only

thank you in advance

 

[moltenmetal]

If your service is clean liquid or gas, there is no velocity limit for valve internals with respect to erosion.

If your service is a slurry or contains particles, or is subject to erosion/corrosion (i.e. sulphuric acid in carbon steel where iron sulphate passivates the ID of the pipe), then there are very restrictive velocity limits- for slurries those may be both maximum and minimum velocities- which vary from service to service.

Sonic velocity in gases will make noise in the valve, and will also ensure that further reductions in pressure in the downstream piping will not increase the flow through the valve. Is that a velocity limit? Depends on your situation. There are lots of valves in gas service where flow is choked (sonic).

 

[LittleInch]

1) As MM says up to the sonic velocity, no for clean fluids, but with any particle sin it - yes.
2) This is for a simple orifice only or single stage regulator. Mass flow rate though is still variable by means of increasing upstream pressure and hence density for gases.
3) No maximum limit other than a practical one. The resistance to flow will vary by valve type and internal design

Bit of a vague question

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way