Design Considerations For Cryogenic Liquid Pumps
Low temperature liquid pump should pay attention to the following problems when designing the structure:
(1) the structure should be symmetrical in order to ensure that the parts are cooled uniformly at low temperature.
(2) the inlet and outlet pipelines of the pump must have the compensation of cold shrinkage, such as metal bellows compensation;
(3) the connection parts between the normal temperature zone and the low temperature zone should be made of materials with low thermal conductivity to reduce the heat conduction loss;
(4) reduce the heat capacity of the components in the low-temperature area as much as possible to reduce the evaporation loss of the liquid and shorten the starting time;
(5) work in low temperature area and have relative moving parts, and choose materials that are close to the linear expansion coefficient as much as possible; The linear expansion coefficient of the enveloping part should be less than or equal to the linear expansion coefficient of the enveloped part to prevent the card death during cold contraction.
(6) on the work of the important parts in low temperature, especially for those who are very strict coupling high movement parts (such as the shaft seal ring and static ring, plunger pump plunger and the cylinder liner, etc.) before a final finishing, must be cold treatment. The cold treatment temperature should be lower than or equal to the working temperature, and the processing time is 1 ~ 4 hours;
(7) in order to prevent the vaporization of cryogenic liquid, special attention should be paid to the pump body and import pipe insulation, usually with perlite or foaming materials, the low temperature of liquid hydrogen and liquid helium pump is often use vacuum insulation;
(8) sealing is one of the key problems in the design of cryogenic pump. There are three types of shaft seal: mechanical seal (with dry and wet type), labyrinth seal and stuffing box seal. For low temperature pumps, mechanical seals are often used.