Purge Equipment

There are several different types of purging equipment – the tee purge, the cross purge, and purge panels (panels will be covered in a future posting). The type of equipment selected depends on the gas service, purity requirements, and budget. 

REDUCE SYSTEM CORROSION - All of these devices reduce moisture in corrosive gas service, and will extend the life of equipment in the process stream by preventing/reducing acid build up. 

PRESERVE GAS PURITY - Purge devices help prevent/reduce inbound contamination of UHP streams during equipment changeovers. 

REDUCE RELEASE OF TOXIC GASES - Cylinder connections, regulators, and process lines can be purged prior to cylinder change to prevent the escape of hazardous gas into the work area during cylinder change outs. 

Tee Purge

The Tee Purge is the simplest piece of equipment used for purging gases for safety and purity, and is usually installed on the inlet of a regulator, and connected directly to the cylinder valve. Since there is no vent or isolation valve on a tee purge, it requires a line purge, through the regulator, down stream to a vent, to a safe area prior to loosening the CGA connection. 

Recommended Gas Service: Flammable gases (not pyrophoric), low ppm concentrations of semi-corrosives (ex.: SO2, H2S), mild toxics with a TLV greater than 25 ppm. 

Purity: Allows for a continuous supply of purge gas through the CGA while changing the cylinder, reducing the amount of moisture and Oxygen that enters the line during cylinder change Moisture and Oxygen can be reduced in the regulator and process lines by purging after cylinder change. A tee purge can help maintain 4.5 – 5.0 levels of purity. 

Drawbacks: Requires more purge gas and longer purge times than cycle purging, while not reducing the impurity levels as low as cycle purging. 

Cross Purge

The Cross Purge is an economical piece of equipment used for cycle purging gases for safety and higher purity levels, and is usually installed on the inlet of a regulator, and connected directly to the cylinder valve. The cross purge includes both a vent and isolation valve, and can be used with vacuum assist. 

Gas service: Flammable gases, pyrophoric, corrosives, toxics. 

Purity: Allows for cycle purging before and after gas cylinder change out. The isolation valve reduces the amount of volume that needs to be purged during cylinder changes by isolating the regulator and downstream system, saving time and gas. 

Cycle purging can reduce the amount of contaminates to sub ppm levels. The vent valve can be connected to a vacuum to enhance the purge cycle, reducing contaminates further. 

Allows for a continuous supply of purge gas through the CGA while changing the cylinder, reducing the amount of moisture and Oxygen that enters the line during cylinder change. 

Allows for purging the process line if required. Moisture levels can be reduced dramatically with a complete cycle purge. Can maintain 6.0 levels of purity. 

Drawbacks: When connected to the inlet of a regulator, the assembly must be supported in some way to prevent bending / kinking of the process tubing after the regulator.