My Boss asked me to provide him with throttling valve in the following condition, I am still a rookie and wonder how to solve:
he would like a Cv of 40 based on his data:
Operation: Start-up, 3 years, Typical (3 years)
Fluid: Water
Water - Total dissolved solids: 5,100 ppm
Water - Chloride concentration 2,600 ppm
Water (pH): 9.3
Temperature: 22, 15, 19
SG: 1.0
Upstream Pressure (Bar): 7.7, 12.5, 10.0
Pressure Drop Bar: 6.7, 11.5, 9.0
Flow Rate (m3/hr): 47.6
Materials of Construction: advise (me)
No. of Reject Valves Required: 4 units.

I am asking where to start, how do I compute my boss' above data with my existing valve data below to see if we are within the operating range.
Existing Valve:
1,2, and 3" sizes
Working Pressure: 5000 psi Max.
Max Pressure Drop: 45000 psi Liquid
Temp.: -20F to 450F
Body config.: "Y", ANgle
End Connection: NPT, Socket-Weld, Flanged.
Trim: Linear Cage.
Flow Direction: Over & Under Plug.
Repeatability: 2%
Shut off: Bubble Tight @ Rate Pressure
Actuation: Manual Handwheel or Electric Actuation.

** If we can use the existing valve with the proposed condition, then what type of Trim to be used. I sincerely appreciate for whoever paying attention to this posting.

In sizes through four-inch you should assume a globe control valve.  Other patterns could be justifyable in larger sizes by this appears to be a globe application due the the ratio of pressure drop to inlet pressure.

For most control valve bodies we select material consistent with the piping system.  If the piping is carbon steel we select carbon steel for the control valve body.  Steel is just fine for most water.  The pH is not extraordinary.

Instead of selecting theindividual internal components, control valve manufacturers such as Fisher offer internal trim kits with appropriate hardness and compatible soft goods.  The catalog provides a temperature/pressure drop table for trim selection - or elimination.  However, you must consult seperate tables to assure that the elastomers are compatible with the fluid.

Water is an easy fluid for the elastomers.  Curiously enough, water with a high inlet pressure and low outlet pressure (high drop) is problematic for your internal metallic components.

Your inlet pressures are not significant.  However, the drop is a substantial part of the inlet pressure.  This suggests low vena-contracta pressure and the possibility of cavitation.  Don's sweat it.  The sizing programs know the physical properties of water and will predict cavitation if it is a problem.

Call your control valve sales person.  They will provide free training for control valve sizing along with the catalogs and sizing program - all available via CD-ROM.  There are manufacturers besides Fisher.  Consider Valtek, Masoneilan, ABB Kent may sell valves in your part of the woods.

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