Why Purge?

Nearly all materials contain some degree of moisture. This often occurs naturally in a component or product and is retained in the form of water vapour. Modern systems which use printed circuit boards, wires, electronic components, rubbers and plastics in their construction will have potentially significant amounts of moisture.

The amount of in-built moisture often described as “hygroscopic moisture” can be significant in comparison to the moisture (water vapour) contained within the air of the same system.

Systems which are required to operate reliably in all the various environments found around the world can be adversely affected by hygroscopic moisture which encourages corrosion. Fluctuating ambient temperatures can lead to the formation of condensation or frost.

Effective purging with dry gas can remove both the moisture combined in the air and the hydroscopic moisture.

What are the Different Purging Methods?

There are a number of methods available to purge a system which depends on several factors including the system operating pressure, air leakage standard and the dryness level required.

The NEPS1000 Advantage configuration offers ability to single point purge, through purge and purge with full gas control. Including an option to determine and monitor the removal of in-built hygroscopic moisture.

Single Point Purge

Traditional conditioning with dry nitrogen, gas or air depends on the flow of gas from an entry connection to an outlet port. In this mode the gas will follow the simplest and easiest path to the outlet connection. This can often lead to “pockets “of unconditioned gas. Using NEPS1000 advantage, the mode of operation changes to a more efficient single connection purging process. This allows also a choice of three selectable pressure cycles to ensure the dry gas influences all the space volume within equipment.

During the purge process the NEPS1000 advantage monitors the pressure and when the pre-selected setting is achieved the supply gas is isolated. Internal control valve allows the gas to flow to the exhaust port where the dewpoint of the mixed air/gas is measured and displayed on the readout. The typical cycle time depending on the equipment volume is 15-20 seconds.

The purging process then continues until the desired dewpoint protection has been achieved. The dewpoint protection level will depend on the equipment application.

An animated simulation of the purge process can be seen, if you click here

Single point purging requires a single entry point to the system typical size adaptors range from M3 to M30 (1/8th to 1.25 inches).

This is the most efficient method of purging as the purge gas achieves mixing and dispersion within the equipment during purging and the resultant mix is returned to the NEPS1000 Advantage for dewpoint measurement.

Multiple Purge

This is an often under used method of purging and simply requires systems to be coupled (ganged) together using adaptors and branch connectors. The pressure cycling function of the NEPS1000 Advantage ensures that the overall pressure is controlled to effectively purged all the connected systems.

Through Purge

This method is less efficient than single point purging but can be improved by monitoring the outlet dewpoint dryness during the purging process.

Two point purging is used when a system has a high air leak rate (azimuth/dynamic sealed systems) or the system is sensitive to internal pressure build up.

The ideal installation for two point purging is to have the gas entry and exit points located as far apart as possible (if practical) This encourages the mixing and dispersion of gas through the system.

The NEPS1000 Advantage remote dewpoint sensor option is ideally suited the two point purging and can be used with the single operation dewpoint control function.

DRYCAB Purge

This type of purging is the ideal method when dealing with small items. Once you have selected the items you wish to purge you place them in a purging cabinet which has a remote dewpoint sensor and a pressure relief valve attached. With this method you are able to attach a moisture trap to the exhaust valve on the NEPs, so if you weigh the trap before and after the operation you are able to tell how much moisture has been removed.

What is Remote Sensing?

The remote sensor option of the NEPS1000 Advantage allows the dewpoint sensor to be located in the system to be purged or in the case of through purging located at the outlet port or connection to monitor the progress of the purging process.

All NEPS1000 Advantage versions can be readily modified with a remote sensing adaptor kit which allows the dewpoint sensor to be located up to 3 metres from the NEPS1000 Advantage control unit.

The remote dewpoint function is operational in all three control modes.These are (off), (once) and dewpointstat control for the dry gas supply.

Effective use of the dewpointstat control function of the NEPS1000 Advantage can only be achieved when the remote sensor is directly mounted into the system enclosure or housing.

Remote sensing can also be used with the pumped NEPS1000 advantage and low voltage versions.

What is the Dewpoinstat Function?

The Dewpoinstat function of the NEPS1000 Advantage is able to monitor and control the removal of in built hygroscopic within a system or equipment. The operation of the Dewpoinstat is fully automatic and only requires the operator to set the control level (dewpoint) required.

The Dewpoinstat requires the dewpoint sensor to be installed in direct contact within the internal volume space of the system or equipment to be purged.

What is Moisture Sensing Technology?

The dewpoint sensor used within the NEPS system provides a reliable measurement system for low water vapour concentrations. The sensor monitors the change in water vapour concentration by measuring a change in capacitance. A porous active layer is sandwiched between two conductive plates.

The sensor responds very rapidly to changes in applied moisture especially from dry to wet. The sensor offers an accuracy of up to 2°C dewpoint and excellent long-term reliability.

Why Nitrogen?

Nitrogen is an ideal gas for the protection of systems and equipment from the effects of humidity contamination and corrosive oxidation.

The natural atmosphere contains more than 70% of nitrogen gas. This abundance of gas means it is easy and cost effective to produce making it suitable for a wide variety of industrial applications.

Nitrogen is a stable and safe gas which is fails to support combustion and has no or very limited reactive capability with other elements when compared to oxygen. Nitrogen gas is widely used for nitrogen blanketing to prevent moisture adsorption and product deterioration.

For the majority of industrial applications nitrogen is produced with a minimum of water content and free of residual oxygen.

Standard bottled nitrogen gas is produced with less than 10 ppm (parts per million) of moisture. To explain this as a practical description a moisture content of 10 ppm is equivalent to a dewpoint of -60°C. The dewpoint temperature of a gas is the temperature to which the gas must be cooled before precipitation in the form of condensation or frost below freezing will occur.

Nitrogen gas is widely favoured for many manufacturing processes particularly when a dry and oxygen free environment is required,

The manufacture of semi-conductors and electronic components is a typical example of such an application. Many products and components are “back filled” with ultra dry nitrogen for life time protection and reliability.

Nitrogen is also used to protect optical assemblies, high voltage switchgear, electronic systems, waveguides and instrument housings.

Why Use Nitrogen?

Generally nitrogen is dry which makes it ideal for purging. The other properties it exhibits are, it is chemically inert with most metals and materials. Nitrogen is ideal for applications which require oxygen to removed in order to minimise any oxidation issues.

What is Dry Nitrogen Purging?

Dry Nitrogen purging can be a multi rolled process;

• A technique for removing hygroscopic moisture (in-built) and creating a very dry micro-climate with an equipment or system. This process allows equipments to operate under a wider environmental temperature range without moisture related failures occurring.
• A technique for the exclusion of oxygen. This then reduces the possibility of oxidation issues, typical example laser systems and the generation of ozone.

How is Dry Nitrogen used for Purging?

Dry nitrogen can be used in exactly the same manner as any other dry purging gases;

• Single point pressure cycling
• Two point through purging/flushing
• Back fill pressurisation

How Dry is Dry Nitrogen?

Commercially produced oxygen free nitrogen (white spot) is generally produced with a moisture content of around 2 ppm (-70°C/-94°F). Typically though once the nitrogen has been decanted down; transported and filled into small bottles the dewpoint could have fallen to between -40°C/-50°C.

Dry nitrogen can also be produced from nitrogen generators using PSA techniques or from cryogenic plants.