SIZE_CV_LIQUID

This function calculates the required metric control-valve coefficient K_v for liquid service using the IEC 60534 liquid sizing method. It evaluates the required valve capacity from liquid properties, vapor-pressure limits, pressure conditions, viscosity, and target volumetric flow.

The sizing objective can be represented as:

K_v = g\left(\rho, P_{sat}, P_c, \mu, P_1, P_2, Q\right)

where g(\cdot) is the IEC-compliant liquid-flow model that captures pressure-recovery effects and cavitation-related constraints through valve factors.

Excel Usage

=SIZE_CV_LIQUID(rho, psat, pc, mu, p_in, p_out, q, fl, fd)

rho (float, required): Density of the liquid at the inlet [kg/m^3]
psat (float, required): Saturation pressure of the fluid at inlet temperature [Pa]
pc (float, required): Critical pressure of the fluid [Pa]
mu (float, required): Viscosity of the fluid [Pa*s]
p_in (float, required): Inlet pressure of the fluid before valves and reducers [Pa]
p_out (float, required): Outlet pressure of the fluid after valves and reducers [Pa]
q (float, required): Volumetric flow rate of the fluid [m^3/s]
fl (float, optional, default: 0.9): Liquid pressure recovery factor (0 < fl <= 1)
fd (float, optional, default: 1): Valve style modifier (0 < fd <= 1)

Returns (float): Metric Kv valve coefficient (float), or error message string.

Example 1: Basic control valve sizing

Inputs:

rho	psat	pc	mu	p_in	p_out	q	fl	fd
965.4	70100	221200000	0.00031472	680000	220000	0.1	0.9	0.46

Excel formula:

=SIZE_CV_LIQUID(965.4, 70100, 221200000, 0.00031472, 680000, 220000, 0.1, 0.9, 0.46)

Expected output:

164.995

Example 2: With default FL and FD values

Inputs:

rho	psat	pc	mu	p_in	p_out	q
1000	2337	22064000	0.001	500000	300000	0.05

Excel formula:

=SIZE_CV_LIQUID(1000, 2337, 22064000, 0.001, 500000, 300000, 0.05)

Expected output:

127.336

Example 3: Different FL and FD values

Inputs:

rho	psat	pc	mu	p_in	p_out	q	fl	fd
965.4	70100	221200000	0.00031472	680000	220000	0.1	0.6	0.98

Excel formula:

=SIZE_CV_LIQUID(965.4, 70100, 221200000, 0.00031472, 680000, 220000, 0.1, 0.6, 0.98)

Expected output:

238.205

Example 4: Low flow rate application

Inputs:

rho	psat	pc	mu	p_in	p_out	q	fl	fd
800	1000	15000000	0.0005	400000	350000	0.001	0.85	0.9

Excel formula:

=SIZE_CV_LIQUID(800, 1000, 15000000, 0.0005, 400000, 350000, 0.001, 0.85, 0.9)

Expected output:

4.55572

Python Code

Show Code

import math

from fluids.control_valve import size_control_valve_l as fluids_size_control_valve_l

def size_cv_liquid(rho, psat, pc, mu, p_in, p_out, q, fl=0.9, fd=1):
    """
    Calculates the flow coefficient (Kv) of a control valve passing a liquid according to IEC 60534.

    See: https://fluids.readthedocs.io/fluids.control_valve.html#fluids.control_valve.size_control_valve_l

    This example function is provided as-is without any representation of accuracy.

    Args:
        rho (float): Density of the liquid at the inlet [kg/m^3]
        psat (float): Saturation pressure of the fluid at inlet temperature [Pa]
        pc (float): Critical pressure of the fluid [Pa]
        mu (float): Viscosity of the fluid [Pa*s]
        p_in (float): Inlet pressure of the fluid before valves and reducers [Pa]
        p_out (float): Outlet pressure of the fluid after valves and reducers [Pa]
        q (float): Volumetric flow rate of the fluid [m^3/s]
        fl (float, optional): Liquid pressure recovery factor (0 < fl <= 1) Default is 0.9.
        fd (float, optional): Valve style modifier (0 < fd <= 1) Default is 1.

    Returns:
        float: Metric Kv valve coefficient (float), or error message string.
    """
    try:
      def validate_positive(value, name):
        try:
          val = float(value)
          if val <= 0:
            return None, f"Error: {name} must be a positive number."
          return val, None
        except (ValueError, TypeError):
          return None, f"Error: {name} must be a numeric value."

      def validate_non_negative(value, name):
        try:
          val = float(value)
          if val < 0:
            return None, f"Error: {name} must be a non-negative number."
          return val, None
        except (ValueError, TypeError):
          return None, f"Error: {name} must be a numeric value."

      def validate_range(value, name, low, high):
        try:
          val = float(value)
          if val <= low or val > high:
            return None, f"Error: {name} must be between {low} (exclusive) and {high} (inclusive)."
          return val, None
        except (ValueError, TypeError):
          return None, f"Error: {name} must be a numeric value."

      # Validate input parameters
      rho, err = validate_positive(rho, "rho")
      if err:
        return err

      psat, err = validate_non_negative(psat, "psat")
      if err:
        return err

      pc, err = validate_positive(pc, "pc")
      if err:
        return err

      mu, err = validate_positive(mu, "mu")
      if err:
        return err

      p_in, err = validate_non_negative(p_in, "p_in")
      if err:
        return err

      p_out, err = validate_non_negative(p_out, "p_out")
      if err:
        return err

      if p_out > p_in:
        return "Error: p_out must be less than or equal to p_in."

      q, err = validate_non_negative(q, "q")
      if err:
        return err

      fl, err = validate_range(fl, "fl", 0, 1)
      if err:
        return err

      fd, err = validate_range(fd, "fd", 0, 1)
      if err:
        return err

      # Check for non-finite values
      if any(not math.isfinite(val) for val in [rho, psat, pc, mu, p_in, p_out, q, fl, fd]):
        return "Error: All parameters must be finite numbers."

      # Call the actual function from the fluids library
      try:
        result = fluids_size_control_valve_l(
          rho=rho, Psat=psat, Pc=pc, mu=mu, P1=p_in, P2=p_out, Q=q, FL=fl, Fd=fd
        )
        if not isinstance(result, (int, float)) or not math.isfinite(result):
          return "Error: Result is not a finite number."

        return result
      except Exception as e:
        return f"Error: Failed to compute liquid valve sizing: {str(e)}"
    except Exception as e:
      return f"Error: {str(e)}"

Online Calculator

rho *

Density of the liquid at the inlet [kg/m^3]

psat *

Saturation pressure of the fluid at inlet temperature [Pa]

pc *

Critical pressure of the fluid [Pa]

mu *

Viscosity of the fluid [Pa*s]

p_in *

Inlet pressure of the fluid before valves and reducers [Pa]

p_out *

Outlet pressure of the fluid after valves and reducers [Pa]

q *

Volumetric flow rate of the fluid [m^3/s]

Liquid pressure recovery factor (0 < fl <= 1)

Valve style modifier (0 < fd <= 1)