How to Select Cryogenic Pumps

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Cryogenic pumps are pumps designed to move coolants and cryogenic liquids. They are built to withstand and operate in extremely cold temperatures. Many of these pumps feature hermetically sealed designs to minimize heat leakage from the motor or contamination by process fluids into the cryogenic fluid. Cryogenic pumps are used to circulate coolant in a variety of applications, including cooling high temperature superconducting cables or magnets, for cooling synchrotron beamline crystals, and as pumps in prototype slush hydrogen applications.

Types

The two fundamental pump types are dynamic pumps and positive displacement pumps.

• Dynamic pumps, and their subtype centrifugal pumps, utilize fluid momentum and velocity to generate pump pressure. Most cryogenic pumps are centrifugal pumps, which typically provide higher capacities than other types of pumps.
• Positive displacement pumps utilize expanding and contracting cavities through which the fluid travels. They provide steady, low capacity flow and high pressure suited for high pressure systems and more viscous fluids.

For more information on pump types, visit the Industrial Liquid Handling Pumps information page on GlobalSpec.

Designs

Cryogenic pumps are typically constructed in long shaft or submersible designs depending on the system setup and application.

• Long shaft cryogenic pumps are designed with the pump motor and mounting flange separated from the pump impeller by a long shaft. The pump impeller is submerged in the cryogen or freezing liquid. This minimizes the leaking of heat from the motor into the frozen or freezing cryogenic fluid. Long shaft cryogenic pumps may be welded or bolted to a variety of cryogenic equipment, including dewars and cryostats.
• Submersible cryogenic pumps are frequently used in applications where heat leak is not the most important factor. Submersible cryogenic pumps are used as pumps in vehicles that use liquefied natural gas or in the liquid hydrogen propellant system in a rocket.

Cryogenic pumps for use in extremely cold environments are usually constructed with a vacuum housing to provide a barrier between the motor and the cryogenic fluid.

Specifications

The primary specifications to consider when selecting condensate pumps are flowrate, pump head, pressure, horsepower, power rating, outlet diameter, and operating temperature.

• Flowrate, also called capacity, describes the rate of volume discharge through the pump, given in gallons per minute (gpm), gallons per hour (gph), or gallons per day (gpd) depending on the size of the pump.
• Head defines the energy supplied to liquid (per unit weight) by the pump. It is expressed as a column height of liquid (either vertical lift or suction), given in feet of head (ft).
• Pressure describes the operating pressure of the pump. It is usually given in pounds per square inch (psi) or bar.
• Horsepower indicates the output power of the pump, measured in units of horsepower (hp).
• Power rating indicates the power required to operate the pump, measured in Watts (W) or horsepower (hp). In the case of electric pumps, some manufacturers will instead specify the required voltage (in volts or V) and current (in amps or A). The power rating is the product of the voltage and current ratings (power = voltage x current).
• Outlet diameter is the size of the discharge or outlet connection of the pump. Inner diameter (I.D.) describes the size of the inner opening while outer diameter (O.D.) specifies the entire opening size including the pipe thickness.
• Operating temperature defines the range of temperatures or the maximum media temperature that the pump can handle. In the case of cryogenic pumps, a minimum temperature rating is often provided to indicate the lowest temperature fluids it can handle effectively.

For a more in depth understanding of pump specifications, performance curves, and operation, visit the Industrial Liquid Handling Pumps information page on GlobalSpec.

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