(655e) A New Model for the Sizing of Needle Type Control Valves in the Laminar, Transitional and Turbulent Flow Regimes

Control valves for low flows of liquids,
even of low viscosity, must be sized to take into account laminar or
transitional flow in the valve trim.

We have found that the equation below
allows the accurate sizing of control valves with seat-guided type trims for
laminar, transitional and turbulent flow:

A single new parameter  QUOTE   is used to adjust the sizing of families of
valve trims of similar geometry, for viscosity dependence in the laminar and
transitional regions. 

This new
parameter has a value of approximately 0.14 for seat-guided annular needle-type
trims such as those used in Badger Research Control Valves and for Jordan LowFlow control valves for trims of C_v. 0.06 and
smaller.   A single Samson valve of
similar trim type was tested and found to have an  QUOTE    of
0.18, which we suggest to use for valves of similar design for conservative
trim sizing in the absence of other data.  We found  QUOTE   to be approximately constant with varying stem
position for trims of this geometry. 

For seat-guided
vee-groove control valve trims manufactured by
Emerson (Baumann), the value of  QUOTE   is approximately 0.06 at full open, and tends
to smaller values as the valve is closed.

This equation can be solved to be explicit
in Q and tends to the normal turbulent flow Cv sizing equation when the product  QUOTE   is sufficiently small.