Pressurized Cryogen Dewars
Pressurized Cryogen Dewars
Cryogenic liquids such as liquid nitrogen and argon are dispensed from pressurized dewars that vary in capacity between 60 and 265 liters. These large, pressurized dewars can be used for dispensing liquid cryogens, but can also be used when high volumes of gas are required for lab processes.
The equipment described below is a common type of liquid nitrogen dewar used on Penn’s campus. For information about pressurized dewars for other cryogenic liquids, contact EHRS.
Liquid nitrogen service is provided to the labs in one of the two ways described below.
Liquid-nitrogen fill station on campus
The pressurized dewar is owned by the laboratory or department, and is refilled by trained staff on campus.
The dewars owned by Penn labs or departments must be sent to a gas vendor for inspection and maintenance whenever the equipment shows signs of malfunction or damage. Contact EHRS for more information about dewar inspections and repair.
Gas-supply companies
Full dewars are delivered to the building or laboratory by the gas supplier.
The laboratory does not own the dewar. The contract is for the liquid nitrogen product.
Dewars from gas suppliers may not be refilled at Penn liquid nitrogen fill stations.
Industry-standard pressure settings for liquid nitrogen dewars classify them as Low Pressure, Medium Pressure, or High Pressure depending on the operating pressure of the dewar. The pressure rating for the safety relief vent are generally set by the manufacturer as follows:
Low Pressure
22 psig
Medium Pressure
230 psig
High Pressure
350 psig
Low-pressure dewars are used for liquid withdrawal. Medium and high-pressure dewars are used for gas withdrawal. Dispensing liquid from a medium or high-pressure dewar is not recommended as it may cause splashing and/or transfer-line whip and increases the risk of exposure and cryogenic burns. Only low-pressure dewars may be used for dispensing liquid nitrogen.
For more information what is a dewar, please get in touch with us!