Double spiral case of molten salt pump is actually composed of two single volutes that they are relative arrangement. Total area of the two volutes equals to the sum of the throat’s area that they are a single volute. The purpose of double volute is used to eliminate the radial force that it is peculiar to the single volute. But experiments show that:

    The radial force of double volute is greatly reduced. But radial force can’t be completely eliminated. The spiral case is symmetrical on the center line. But the two channel of guiding liquid into the outlet flange is asymmetric. Because of this, the impeller pressure that it is along the circumference is not fully offset and it is still the radial force.
    We have decided the coefficient K value that we are based on pressure distribution of actually measuring the double volute. The data is available to ordinary single-stage double volute pump. If the double volute pump K values decreased significantly, radial force almost equal to zero within the working range of the pump.
    The hydraulic performance of the double scroll pump is close to the single spiral case. The result of experiment shows that the efficiency of the double spiral case pump lowers about 1-1.5% than the single pump.
    In the non optimal condition, the efficiency of the double - scroll pump higher about 2% than the single - scroll pump. Therefore, the efficiency of the double - scroll pump in the whole working range is higher than that of the single - scroll pump。
    Due to the long baffle back flow channel is narrow， it is difficult to product the double spiral case. It almost can’t clean sand. So it should not use double spiral in the small flow of a single pump.
    If you want to know more about the content of the molten salt pump volute design, please see Warwick pump company official website: www.moltensaltpump.com.