def pipe_grav_dp(m_dot=10.0, rho=115.0, z=950.0):
    """

    :param m_dot: mass flow [kg/s], (+) injection, (-) withdrawl
    :param rho: density [kg/m^3]
    :param z: depth/length [m]
    :return delta_p: pressure loss [MPa]
    """

    # gravitational constant
    g = 9.81  # [m/s^2]

    if m_dot > 0.0:  # injection
        delta_p = -rho * g * z
    elif m_dot < 0.0:  # withdrawl
        delta_p = rho * g * z
    else:  # no activity
        delta_p = -rho * g * z

    return delta_p * 1.0e-6