def efficency_vol_poly(cappa):
    """Calculate volumetric efficency for a given pump's typical number.

    The polynomial has been calculated applaying the curve fitting at nodes
    cappa       .2 .3 .4 .5 .6 .7 .8 .9 1.0 1.1 1.2
    eta_hyd     .940 .948 .953 .956 .957 .958 .959 .960 .961 .962 .963
    weights     ones(cappa)
    n           5

    :param cappa (float): typical number
    :return eta_vol (float): volumetric efficency
    """
    coef = [0.907, 0.236, -0.433, 0.378, -0.144, 0.016]
    eta_vol = sum([val * cappa**idx for idx, val in enumerate(coef)])

    return eta_vol