The following problems should be paid attention to in the structural design of cryogenic liquid pumps:
(1) In order to ensure uniform cold shrinkage of parts at low temperature, the structure should be symmetrical;
(2) The inlet and outlet pipes of pumps must be compensated for cold shrinkage, such as metal bellows.
(3) The low thermal conductivity material should be used to make the connecting parts between the normal temperature zone and the low temperature zone in order to reduce the thermal conductivity loss.
(4) To reduce the heat capacity of components working in low temperature zone as much as possible, so as to reduce the vaporization loss of liquid and shorten the starting time;
(5) Parts working in low temperature and moving relatively should be made of materials with similar linear expansion coefficient as far as possible. The linear expansion coefficient of enveloped parts should be less than or equal to the linear expansion coefficient of enveloped parts in order to prevent the cold shrinkage from jamming.
(6) For the important parts working at low temperature, especially for the moving parts with strict coupling requirements (such as the dynamic and static rings of the shaft seal, the plunger and cylinder liner of the plunger pump, etc.), cold treatment must be done before the final finishing. The cold treatment temperature should generally be lower than or equal to the working temperature, and the treatment time should be 1 to 4 hours.
(7) In order to prevent the vaporization of cryogenic liquids, special attention should be paid to the insulation of the pump body and the inlet pipeline. Generally, pearlite or foaming materials are used. Vacuum insulation is often used for low temperature liquid hydrogen and liquid helium pumps.
(8) Sealing is one of the key problems in the design of cryopump. The seal of pump is closed or shaft seal. There are three types of shaft seals: mechanical seals (dry and wet), labyrinth seals and stuffing box seals. Mechanical seals are often used for pumps with lower temperatures.
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