K_BUTTERFLY_VALVE

Computes the Crane loss coefficient for a butterfly valve from line size and valve style (centric, double-offset, or triple-offset).

Each style maps to a style factor and friction-based coefficient framework, producing different pressure-loss behavior at the same diameter.

The result is a dimensionless K coefficient for valve minor-loss calculations.

Excel Usage

=K_BUTTERFLY_VALVE(D, bfly_style)

• D (float, required): Diameter of the pipe section the valve is mounted in [m]
• bfly_style (str, optional, default: “centric”): Valve style type

Returns (float): Loss coefficient K for the butterfly valve [-]

Example 1: Small centric butterfly valve

Inputs:

D
0.1

Excel formula:

=K_BUTTERFLY_VALVE(0.1)

Expected output:

0.732981

Example 2: Double offset butterfly valve

Inputs:

D	bfly_style
0.1	double_offset

Excel formula:

=K_BUTTERFLY_VALVE(0.1, "double_offset")

Expected output:

1.20535

Example 3: Triple offset butterfly valve

Inputs:

D	bfly_style
0.1	triple_offset

Excel formula:

=K_BUTTERFLY_VALVE(0.1, "triple_offset")

Expected output:

3.55088

Example 4: Large centric butterfly valve

Inputs:

D
0.5

Excel formula:

=K_BUTTERFLY_VALVE(0.5)

Expected output:

0.294561

Python Code

Show Code

from fluids.fittings import K_butterfly_valve_Crane as fluids_k_butterfly_valve

def k_butterfly_valve(D, bfly_style='centric'):
    """
    Calculate the loss coefficient (K) for a butterfly valve using the Crane method.

    See: https://fluids.readthedocs.io/fluids.fittings.html#fluids.fittings.K_butterfly_valve_Crane

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

    Args:
        D (float): Diameter of the pipe section the valve is mounted in [m]
        bfly_style (str, optional): Valve style type Valid options: Centric, Double Offset, Triple Offset. Default is 'centric'.

    Returns:
        float: Loss coefficient K for the butterfly valve [-]
    """
    try:
      try:
        D = float(D)
      except (ValueError, TypeError):
        return "Error: D must be a number."

      if D <= 0:
        return "Error: D must be positive."

      style_map = {
        'centric': 0,
        'double_offset': 1,
        'triple_offset': 2
      }
      style_int = style_map.get(bfly_style)
      if style_int is None:
        return "Error: Invalid bfly_style."

      result = fluids_k_butterfly_valve(D=D, style=style_int)
      return float(result)
    except Exception as e:
      return f"Error: {str(e)}"

Online Calculator

D *

Diameter of the pipe section the valve is mounted in [m]

bfly_style Optional Centric Double Offset Triple Offset

Valve style type