Cryogenic pumps,?
Answer:
*The Cryogenic Pumps are used for handling liquids such as oxygen and nitrogen, at temperatures as low as -320°F.
*The top suction design of pump has become a standard in the industry for handling fluids which are near or at boiling point.
*Since most cryogenic pumps operate close to the boiling point of liquid, the best design solution is to use a vertical, top suction unit to prevent vapor binding.
*Design considerations for cryogenic pumps include special metallurgical considerations due to low temperatures and flammability of liquified gases such as liquid oxygen, thermal expansion and contraction and material behavior at cryogenic temperatures, and extremely low NPSH.
*Top suction design prevents vapor binding while providing rapid venting and continuous priming.
*All impellers, whether single stage or multi-stage designs, are supported by precision sleeve bearings which are positioned above and below every impeller stage. This bearing configuration maintains the close tolerances required for efficient pumping of cryogenic liquids.
[The word cryogenics literally means "the production of icy cold"; however the term is used today as a synonym for the low-temperature state. It is not well-defined at what point on the temperature scale refrigeration ends and cryogenics begins. The workers at the National Institute of Standards and Technology at Boulder, Colorado have chosen to consider the field of cryogenics as that involving temperatures below –180 °C (93.15 K). This is a logical dividing line, since the normal boiling points of the so-called permanent gases (such as helium, hydrogen, neon, nitrogen, oxygen, and normal air) lie below -180 °C while the Freon refrigerants, hydrogen sulfide, and other common refrigerants have boiling points above -180 °C.
Recent research regarding superconductivity at low temperatures has been called cryoelectronics, and the utilization of these sciences is called cryotronics.]
*[CRYOGENIC MATERIALS Cryogenic materials have special properties that make them particularly hazardous to use in the solid, liquid or gaseous states. Cryogenic materials are characterized by severe low temperature (-60°C to -270°C). Most cryogenic liquids are odorless and tasteless when vaporized; however, when exposed to the atmosphere they create a highly visible dense fog that dissipates with warming. Cryogenic temperatures are achieved by liquefaction of gases, most commonly helium, hydrogen, nitrogen, argon, oxygen or methane.]
Cryogenic pumps mean pumps handling cryogenic fluid at very low temperature e.g - 180 deg c to - 190 deg.c for liquid O2/ N2/H2/Ar etc. These pumps have to be made of special material of construction / special glands suitable for low temperature service.
Swapan is correct. The materials used for their construction is the big difference, usually a stainless steel. Another distinction with many pieces of cryo equipment is that they tend to have longer 'shafts' such as the drive shaft on a pump or the valve shaft to enable adequate insulation to be applied. There are some cryo pumps that are totally encapsulated, motor and all, as well.
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