Septum Needles

Traditionally the needles incorporated in septum assemblies used within sampling equipment available for the chemical and pharmaceutical industries, have been based on the same design as hypodermic needles. Still today many other sampling equipment manufacturers are supplying this outdated style of needle in their products. The needles are manufactured from thin wall small bore tube which is cut at an angle at the end to pierce the septum.

This needle design has a severe inherent problem which can cause toxic leaks from the septum assembly straight into the atmosphere. This is because of the tubular design of the needle, which every time a septum capped bottle is offered up into the assembly the needles cut a slug the same diameter as their bore out of the silicone / PTFE septum. 

This slug of material is deposited by the filling needle in to the sample not causing any hazard. However the slug trapped in the vent needle sits there gradually being drawn up the needle with the gas being evacuated by the bottle. Over subsequent samples a new slug is deposited in the vent line needle, every sample depositing another small disc of silicone, Before long sufficient material is deposited within the vent needle and vent path to effectively block this needle. When this happens the needle stops functioning as a vent. When the next sample is taken the mix of potentially toxic gas and air first pressurizes the sample bottle, which is definitely not recommended, then this pressurized gas pushes past the silicone seal around the needles straight into the atmosphere. 
CRP's Septum assemblies are always supplied with non coring type needles. These needles are not manufactured from small bore tube, they are precision machined from solid bar. This needle design is unique from others, the end of the needle is machined to a point which cleanly punctures the septum without cutting any material from it. The sample media travels down the needle then through 90 degrees before filling the sample bottle. The vent is identical in not creating any slugs of material from the septum eliminating the problems affecting other designs. 
Our septum assemblies use two separate needles which can easily be replaced individually. Others have welded assemblies which means both needles have to be replaced at once. The needles are available in several bore sizes from 0.8mm to 3mm. All our needles are manufactured from Hastelloy C276 for almost universal use in corrosive & non corrosive applications. They are sealed to the septum dip tube with Chemraz 'o'rings.

The needles are based on a modular mounting design where suitable and can be swapped out for different bore size needle on site if required with the minimum of tools and down time.

For applications where very small volume septum samplers are required this can cause issues where the aperture diameter in the septum is too small to fit 2 needles through. For these applications CRP has designed a special non-coring needle with integral vent allowing very small bottles to be used with only one needle fulfilling both the filling and venting operations.

Contact Details

Corrosion Resistant Products Ltd
Todmorden Road
OL15 9EG

Phone: +44(0)1706 756400
Fax: +44(0)1706 379567