Cryogenic Fluid:
A liquid maintained at extremely low temperatures, typically below -100°C. Common examples include LNG (Methane) at -162°C, Liquid Nitrogen at -196°C, and Ethylene at -104°C.
Submerged motor cryogenic pump:
A specialized centrifugal pump designed specifically for handling cryogenic fluids such as Liquefied Natural Gas (LNG), LPG, and liquid nitrogen. Unlike traditional designs that used long shafts to keep the motor separate from the cold liquid, these units feature a completely integrated motor and pump assembly that operates while entirely submerged in the cryogenic fluid.
Submerged Motor:
An electric motor specifically engineered to operate while fully immersed in the process fluid (like LNG), which serves as both a high-efficiency coolant and a lubricant for the internal bearings
Retractable In-Tank Pump:
A design configuration that allows the cryogenic pump to be installed or removed through a pipe column while the tank contains liquid, utilizing a suction foot valve to isolate the pump from the process fluid.
Circulation Pump:
A low-pressure cryogenic pump utilized in large storage tanks to circulate the liquid internally; this prevents “rollover” (stratification) and ensures the liquid remains at a uniform temperature.
Send-out Pump:
A high-pressure, multistage cryogenic pump typically used to feed liquid into vaporizers for gas distribution pipelines or downstream petrochemical processes.
Vessel-mounted (Can) Pump:
A cryogenic pump configuration where the unit is installed within its own suction vessel or “can,” allowing it to be easily integrated into a piping system and act as a phase separator for vapor
Marine or Cargo Pump:
A cryogenic pump type primarily used on LNG carriers, where the unit is fixed in a support system located at the bottom of the tank and discharge piping attaches directly to the pump top.
Spray Pump (Cool-down Pump):
A smaller cryogenic pump used to spray liquid into the tank’s upper sections to cool the system down prior to full cargo loading or to bring down “dead stock” in an emergency.
Impeller:
The primary rotating component that adds energy to the fluid. Cryogenic pumps often use closed, single suction designs
Inducer (Axial Impeller):
A specialized component located at the pump inlet designed to improve suction performance and lower the NPSHR, allowing for “stripping” tanks to very low liquid levels
Diffuser:
A stationary component (often a vertical diffuser type) that directs the flow from the impeller, effectively managing the transition of liquid and any potential vapor.
Wear Rings:
Components used to maintain close clearances between rotating and stationary parts, ensuring hydraulic efficiency and protecting against particulate damage
Thrust Plate:
A stationary internal component that, when paired with the rotating shaft shoulder, defines the critical axial clearances required for the Thrust Equalizing Mechanism to function correctly.
Axial Thrust Balancing System (TEM):
A sophisticated hydraulic mechanism that utilizes a portion of the impeller discharge stream to automatically balance bearing loads across the pump’s entire flow range, preventing mechanical contact and failure.
Suction (Foot) Valve:
A specialized valve used in retractable in-tank installations that allows the pump to be removed or installed without emptying the main storage tank
Stator:
The stationary part of the electric motor, typically made of silicon steel laminated plates and impregnated with epoxy resin to remove trapped air and provide flexibility at cryogenic temperatures
Rotor:
The rotating part of the motor, constructed from laminated plates with aluminum rotor bars pressed or inserted into slots
Electrical Feedthru or Terminal header:
A specialized, hermetically sealed assembly that allows high-voltage power cables to penetrate the cryogenic vessel or tank while maintaining a pressure-tight moisture barrier.
Foot Valve:
A critical component in retractable in-tank pump designs located at the bottom of the column; it allows the pump to be removed for repair even while the tank is full of liquid.
Vibration Detection System (Accelerometer):
A sensor mounted directly to the pump housing that monitors vibration levels. It provides a signal to a remote monitor for real-time troubleshooting and fault detection
Cooldown:
The critical procedural phase where LNG vapor is introduced into the system to lower the pump temperature to a specific threshold (typically –130°C) over a minimum 10-hour period to prevent thermal shock.
Pumpdown:
The operation of stripping or emptying a storage tank to the lowest possible liquid level; as the level reaches the NPSHR datum, flow must be manually reduced to avoid losing prime.
Purging:
The act of displacing the internal atmosphere of a pump or electrical junction box with dry nitrogen gas to eliminate moisture and prevent condensation that could lower insulation resistance.
Differential Shrinkage:
The phenomenon where internal pump components contract at different rates during cooldown due to varying thermal expansion coefficients; this is a critical consideration for maintaining running clearances.
Locked Rotor:
A critical fault condition where the starting current reaches its maximum value but the pump fails to rotate, typically indicating that the unit has mechanically seized and must be removed for repair.
NPSHR (Net Positive Suction Head Required):
The minimum pressure required at the pump’s suction inlet to ensure the process fluid remains in a liquid state and prevents the onset of incipient cavitation.
Cavitation:
The formation and subsequent collapse of vapor bubbles within the process fluid when the pressure drops below the fluid’s vapor pressure, leading to excessive vibration, loss of flow, and potential impeller damage.
DISCLAIMER
This glossary is provided for general informational and educational purposes only. While reasonable efforts have been made to ensure accuracy, TriSeas International, Inc. accepts no liability for any errors, omissions, or decisions made based on this information. This glossary has been prepared based on our engineering knowledge and experience, together with information obtained from various industry references, technical publications, and operating manuals. All trademarks, trade names, and product names are the property of their respective owners and are used for identification and reference purposes only.
Users should always refer to the applicable OEM manuals, industry standards, and qualified engineering professionals before making technical or operational decisions.
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