Exhaust Connection - Thermo Scientific Prima PRO User Manual

Technical Description: Inlet
Rapid Multi-Stream Sampler
The exhaust connection is a 1" O.D. tube stub, suitable for a simple
hose connection or a compression fitting depending on application. It

Exhaust Connection

may be required to heat the exhaust line. This can be just as critical
as the sample lines but is often neglected. Alternatively, the exhaust
line can be configured with a continuous downward slope so that any
condensate will drain away from the valve. If this is not possible, a
trap should be installed to prevent condensate draining back to the
RMS.
The exhaust line size should be selected, giving consideration to the
maximum total sample gas flow, and the length of the line. The
requirement is to generate a negligible back pressure, as any such
back pressure will be flow dependant and may result in variable
conditions at the analyser. For an application where there are a
limited number of sample lines or the lines are all low flow, it may
be possible to reduce the line size to 1/2" for example. At the other
flow extreme, it may be necessary to adapt up to a line size greater
than 1".
The pressure at the exhaust should be within the values specified in
"Inlet
Specification". Any pressure variation will result in a variation
at the analyser, so the pressure stability should also be within
specified limits. Longer term variations outside this range may be
acceptable but will require more frequent instrument calibration. The
easiest way to achieve the required stability is to use a direct
atmospheric vent. However, this is not always possible depending on
the nature of the gas mixture, local environmental regulations, etc.
An alternative, such as a line to a flare, may be used if the above
conditions can be met.
If the exhaust line is shared with other equipment, consideration
should be given to pressure fluctuations that might be caused by that
equipment. In conditions where all sample streams to the RMS are
off, the possibility of back diffusion of gases from the exhaust must
also be considered. For this reason, extreme care must be taken if the
analyser rotary pump is vented to the same exhaust system. The
pump exhaust will contain oil vapour that could contaminate the
RMS and subsequently the mass spectrometer. Where possible, it is
preferable to avoid such a connection.
In some cases, it may be necessary to use a pump to produce a
negative pressure at the RMS exhaust to induce flow in the sample
lines particularly when sample points are at low pressures. This is the
normal operating mode for the Sentinel PRO. Clearly, the pressure
(vacuum) generated by any such pump should conform to the above
requirements.
It is important to remember that all sample gases are mixed in the
common exhaust. There may be situations where combustible or
reactive mixtures are generated. To avoid problems of this nature, a
diluting gas (commonly nitrogen) can be added to the exhaust line or
Thermo Fisher Scientific Prima PRO & Sentinel PRO Mass Spectrometers User Guide C-7