GC-MS

The Finest Needle Valves

Feb 02 2017 Comments 0

For many years, designers of GC & GC/MS and other analysis systems have had to modify their schematics to avoid the use of needle valves due to the lack of supply of good, repeatable and reliable valves. This is no longer the case and there are still applications where only a very fine valve that opens with no burst can be used.

Chell's CMV range of stainless steel needle valves have been developed to provide the finest gas flow control over typical ranges of 0-20, 0-1000 & 0-3000 std.cm3min-1 air at 1bar differential pressure. Designed for use in pressure or vacuum applications, they are ideal for control applications in gas chromatography, mass spectrometry inlet, and other gas analysis and blending applications. In other words, any application where ultra-fine & repeatable flow is required.

The valve’s opening characteristics are extremely smooth, preventing bursts of gas which disturb delicate or ultra high vacuum instrumentation. The opening is so smooth that they are frequently used in UHV systems where low flows need to be established into pressures as low as 1 x 10-7 mb. Repeatability is exceptional so that flow settings may be repeated time & time again.

Construction is in S316 Stainless Steel with Perlast® seals for best corrosion resistance & minimum sample contamination. Vacuum rated valves are leak tested on a helium mass spectrometer to <1x 10-8mblsec-1 and their shut-off achieves the same specification. Valves are available with 1mm, 1/16in, 1/8in, 1/4in & 6mm twin ferrule compression fittings and additionally, vacuum models are available with NW10KF fittings.

The CMV was developed specifically for mass spectrometry inlet service, probably the most critical application for such a valve but is eminently suitable for many other critical applications where long-term stability is required. The valve's manufacture has been refined over the years, even including automated computer-controlled high-resolution opening and closing plots using MFC's in order to guarantee the quality of its performance. With the finest needle giving 0-20sccm over 20 turns, this is the finest control valve ever produced.

For those requiring miniature tube couplings, Chell has produced many thousands of couplings for dedicated applications in the aerospace industry that are equally applicable to gas chromatography. Construction is in S316 or S321 stainless steel for tube diameters of 1/16” and 1mm and the design has the absolute minimum of dead volume within the flow path.

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