Circulating pump for high pressure and high temperature applications
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ly operated pump drive. For applications not requiring high temperatures, an electric motor or electromagnetic pump drive could be used. Furthermore, alternative materials could be chosen to match the design to different applications. For example, an all-glass pump with polytetrafluoroethylene  PTFE  or a glass-coated magnetic steel piston and appropriate glass check valves could be fabricated to handle corrosive gases. In any case, radial uniformity along the bore of the housing cylinder and a smooth piston surface are important in maintaining the piston-housing clearance gap to a minimum.
The performance of this pump was more than adequate for our purpose. However, it can be enhanced. Choosing a larger nipple for the main body and redesigning the magnet assembly to give a stronger coupling between the ring magnet and piston are certain to produce higher flow rates and increased pressure heads. For temperatures up to 150 °C, NdFeB can be used as the magnet material. During the design stage we considered a number of alternative piston designs each comprising a cylindrical magnet fitted at each end with pole pieces. According to the FEA, such an arrangement would provide a much greater coupling, as measured by the calculated restoring force on the piston for small displacements from the equilibrium position. For example, the calculated coupling constant for the solid type-440C stainless steel piston was 1.25 N mm−1, whereas composite designs of the same overall dimensions were considered offering up to 4 Nmm−1. However, although larger pressure heads might be obtained, a composite piston of this kind would be more difficult to fabricate to the desired high precision, and adhesives may be required to bond the components together.
Although flow delivery is relatively smooth, some degree of pulsation is unavoidable when the pump is used as a stand-alone item. The addition of in-line devices acting as pulsation dampeners, such as the one described earlier, help to deliver a smoother flow. One possible failure mode of the pump is for the piston to jam in the cylinder bore as a result of small particles becoming lodged between the two. In such case, it is easy to partly disassemble the pump in order to remove the piston and clean the cylinder bore. Though no such problem has yet been encountered with this pump, the use of a filter in the circulation loop is recommended.