def calc_NPSH(P_suction, P_vapor, rho_liq):
    """Return NPSH in ft given suction and vapor pressure in Pa and density in kg/m^3."""
    # Note: NPSH = (P_suction - P_vapor)/(rho_liq*gravity)
    # Taking into account units, NPSH will be equal to return value
    return 0.334438*(P_suction - P_vapor)/rho_liq