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 INSTRUCALC: Control Valves

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Control Valve Sizing

Three programs are available, each for standard and low flow valves:

  • Liquid Flow
  • Gas Flow
  • Two Phase Flow

Options for each valve calculation are:

  • Calculate Valve Size
  • Calculate Flow Rate
  • Calculate Valve Pressure Drop

Three cases are provided for each calculation:

  • Maximum flow
  • Normal flow
  • Minimum flow

Aids for the calculations are -

  • Typical valve data tables
  • Fluid properties at flowing conditions
  • A routine to calculate the valve pressure drop available in the piping system


After using the above for normal flow to determine the valve size, scroll bars will change the flow, recalculate the data and determine the maximum and minimum flows that the piping system will allow.

The programs have a data base of typical valves so that different valve data can be entered into the calculation in order to make the best selection. Try several and calculate until a valve style and size is selected which has the rangeability and does not have cavitation or noise problems. When a final selection is made the exact manufacturers' data can be entered for a final calculation.

Finally, for liquid valves in long piping systems, take the option for the minimum closing time, this is the water hammer program to determine if a special closing time is required to avoid water hammer.

Sizing Philosophy

Each manufacturer has its own formula for determining the valve size, the valve noise and the cavitation characteristics. This program uses the ISA sizing formulas, it uses the Masoneilan noise prediction method and incipient cavitation technique. The object of the program is to determine the valve size, the cavitation, flashing and noise problems and prepare a data sheet suitable for bid purposes. Some manufacturers may differ from these conclusions, usually the variations are minor and do not change the size and style. Occasionally the noise and cavitation characteristics will differ so that engineering judgment may be called for. The failure of a valve because of cavitation erosion can be extremely expensive. Sometimes a change in body style, or hardened trim is sufficient to eliminate the problem,

The typical valve data files are in ASCII format, three options are provided. They are Standard Valves, Low Flow Valves and a file for User Valves. They can be modified from within the program. The Standard file is based on Masoneilan data. The Low Flow file is based on Research Control Valves data. If another manufacturer is preferred edit the User valve file as required. If the manufacturer does not use the incipient cavitation factor (Kc) then leave the box empty. ISA S75 shows data for a typical file.

References
Control Valve Sizing Equations ANSI/ISA S75.01.01-2002
Masoneilan Noise Control Manual
ISA Handbook of Control Valves J. W. Hutchison

 INSTRUCALC: Control Valves

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