FAQ

Usage information when applying HORNUNG high purity gas control equipments

Contamination and prevention of high purity gas:
Contamination by air (humidity) after implementing an equipment or after changing a cylinder, will be removed by multiple purging with changing pressures (up to 10 bar increase/relief) using dry Nitrogen or other inert gases. Contamination caused by inappropriate piping material or inappropriate valves and regulators can be avoided by the consequent application of control equipment with metal diaphragms, gases of high purity, appropriate piping (electropolished), minimisation of dead spaces, usage of orbital welding techniques with Argon inert gas, regular purging and conservation of the piping, avoiding leaks by Helium leakage tests and the usage of VCR fittings.

Use of automatic or manual change over:
An automatic change-over is recommended when a required high gas flow ultimately leads to frequency in cylinder changes, the interruption of gas supply should be avoided, and a non-supervised gas supply over the weekends should be ascertained.

Selection of single or dual stage:
Dual stage regulators should be used when the operating pressure has to be absolutely stable even if the inlet pressure drops (during discharging of cylinder) or if the pressure has to be reduced from a high pressure level (e.g. 200/300 bar) to a very low pressure (e.g. < 1 bar).
When using liquified gases it is sufficient in nearly all applications (e.g. SF6, NH3, HCL, CO2 and others) to use the single stage pressure regulator because the vapour pressure of liquified gases remains constant until the cylinder is nearly empty.

Control in mbar ranges:
High purity pressure regulators are limited in their functions due to the internal metallic components (flexibility of the metal diaphragm). In most cases a compromise has to be made between the quality of the gas and the control capabilities of the pressure regulator with operating pressure below 100 mbar. Analytical processes demands the usage of metal diaphragms or metal bellows components.

Gas purging equipment:
A purging device is recommended for toxic and corrosive gases or for calibration gases with contents of corrosive ingredients (even in ppm- or ppb areas).
Centralised or decentralised gas supply:
A decentralized gas supply from single gas cylinders is useful when gas is needed temporarily or for a few hours. If gases are needed continuously it is recommended to use a centralised gas supply system. A centralised gas supply system offers economical advantages if the same gas will be used at different points of use (less cylinders, less handling, less renting costs, less indoor transport, more safety).

Material choice:
Stainless Steel is used in processes with toxic or corrosive gases. Furthermore it is recommended to use stainless steel materials for processes operating with high purity gases and for calibration gases with corrosive ingredients in the range of ppm or ppb or more. It is sufficient to use copper pipelines or brass materials for non-corrosive gas qualities of up to 5.0. Stainless steel or a special cleaning process is recommended for the gas supply with ECD (electron capture detector) applications.

Relief valve for pressure regulator:
Pressure regulators, used as cylinder or panel regulators, usually have an integrated relief valve with a relief pressure adjusted to the max. outlet pressure.
The primary purpose of the relief valve is to protect the pressure regulator. The protection of sensitive processes after the regulator is achieved with a safety valve.