Eaton Crouse-Hinds Z130, Instruction Manual

Page: 9 / 24

INM MTL 130-0200 Rev 4
5
3.3.2 General advice Sample
The instrument is supplied with one of several sample system types specified by the user on
order. A label on the instrument shows the pressure limits and other data for the particular one
fitted. This should be taken into account before applying a sample.
WARNING
The case should not be exposed to water jets or drips.
For permanently installed analysers it is advisable to fit an isolating valve in the sample delivery
line so that the analyser can easily be removed for servicing. In cases where the sample
exhaust is not vented to atmosphere then a valve may be required there too. The use of a
three-way valve on the inlet side is also useful in allowing easy connection of other gases for
calibration checks.
Dead-legs, particularly those present in Bourdon tube type pressure gauges and some
fittings can take a long time to purge out as can small dead zones. Unnecessary dead-legs
should be avoided.
Most analysers are supplied with a built-in sample flow-regulating valve. If a valve is fitted in
the sample outlet pipe work it is important to remember that it must be the last to be shut.
3.3.3 Measuring low levels of oxygen
All piping should be of good quality material with sound joints and couplings. When measuring
concentrations of less than 500ppm oxygen very small leakages can noticeably affect the
readings- for ppm concentrations the piping must be of hard plastic or metal. Suitable plastics
are Nylon and rigid P.V.C. Soft plastics, P.T.F.E. and flexible P.V.C. are not suitable. Cylinder
pressure regulators should have a low volume and a metal diaphragm. Most pressure gauges
etc. contain cavities that entrain air/oxygen and can take several hours to purge down, for this
reason they should be avoided.
Flow regulating valves are typically poor shut-off valves and vice-versa. Multi-way valves can
also be problematic, particularly if they have a source of pressurised high oxygen gas (air for
instance) connected to one of their ports. If it is necessary to isolate a pressure regulator, a
shut-off valve should be fitted to its outlet port.
If a pump is needed because the sample is at near atmospheric pressure, then it should be
connected to the sample outlet and the sample drawn through the analyser, with the flow
adjustment valve between the analyser outlet and the pump inlet. If the pump is placed at the
sample inlet then it will need to be of a construction that will not contaminate the sample.
Flow meters can introduce leaks at these levels and should be installed in the sample outlet
pipe work.
Before connecting a gas sample to the analyser it is advisable to thoroughly purge the
external gas train.