Removing all moisture with assurance

Written by: Brownell Advertising Feature | Published:

Automatic systems ensure thorough single connection purging of systems and instruments



A range of dry gas purging systems ensures complete removal of moisture from all kinds of components and systems, greatly assisting the long term reliability and usefulness of electronic, optical, high voltage and laser systems. They remove both the moisture in the air and also that used in the materials used to construct them.

Key to the NEPS series of products developed by Brownell in Park Royal, London, is the alternate introduction of dry gas, usually nitrogen, into the item to be purged under excess pressure, followed by exhalation when the issuing gas is assessed for moisture content. Introduction of dry gas under pressure ensures that it reaches all parts of the device to be purged, and also allows materials used in manufacture to outgas. This is in contrast to pumping dry gas through a device, which will always follow the path of least resistance, and will inevitably leave some parts unpurged. The NEPS system also allows the purging of products that can have only a single gas connection point. It can additionally be used to undertake through purging of items that are too delicate to pressurise, or are so small that they are best purged by being placed in a cabinet, by attaching a remote dew point sensor to the exit line.

Brownell director Martin Partridge explained that “Nitrogen in bottles is not always dry” and the NEPS 1000 Dewpoint monitor can be used to check the dryness of the gas prior to commencing the purging operation, which is completely automatic once it has started. Gas can be supplied with a guarantee as to dryness, but this is then significantly more expensive than normal products. The systems are also suited to purging with argon, SF6 and helium, where required.

The user sets the dew point to be achieved and the pressure to which the system is to be pressurised, usually 10.3kPa (1.5psi) above ambient, but it can be 17.2kPa (2.5 psi) or 34.4kPa (5.0 psi). The machine monitors pressure, and when the pre-selected level is reached, the supply gas is isolated and an internal control valve allows the gas to flow to the exhaust port, where the dew point of the mixed air and gas is measured, until the pressure drops to 2.1kPa (0.3psi) above ambient. The purging cycle is then repeated until the desired dew point in the issuing gas has been attained.

Target dew point is typically –40 deg C, but the system can purge to down to –80 deg C. The Dew point sensors do not require re-calibration for twelve months.

But the capabilities of the systems do not end there. They also come with a selection of four built-in leak testing capabilities. Pressure leak rate display resolution is 0.01 psi. Furthermore, they can be used to measure the permeability of membranes and ‘O’ rings by purging special cavities that are sealed by the membranes and ‘O’ rings on successive occasions. Partridge told us that in this way, “In seven to ten days, it is possible to make predictions of equipment life over ten to fifteen years”. The same technique can be applied to measuring sealing integrity generally, purging equipment once, and then doing so a few days later, to see if the dew point has been maintained or has risen.

The systems come in three four versions. The standard version in its carry case is the NEPS 1000 Advantage. The NEPS1000 Pumped as its name suggests, incorporates a pump, so it can use dried air or gas at ambient pressure, instead of depending on compressed gas in a bottle. The NEPS Dual Voltage can be run off 24VDC, 3A for field use, as well as the standard 100 to 230VAC, 50 to 60Hz and the NEPS1900 is designed for 19 inch rack mounting.

All units are NATO approved

Pointers

* The NEPS family of products are designed to purge moisture from enclosed devices by alternately pressurising them with dry gas, and allowing gas to be released, measuring the dew point of the dried as it does so. The cycle is repeated until the desired dew point is reached

* They work with nitrogen, argon, SF6 and helium

* They may also be used for leak testing and for evaluating the permeabilities of membranes and ‘O’ rings, using special test enclosures


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