ESU Installation, Operating and Maintenance Instructions 2
1. INTRODUCTION
The ESU Environmental Sampling Unit is designed to make it easier to monitor gases such as
chlorine and sulphur dioxide which, because they have a high density and are readily absorbed
into many materials, are difficult to detect using conventional point detectors. The explosion proof
version may be used for monitoring heavy flammable gases such as LPG. The ESU uses a
sampling chamber technique in which gas is sampled using an electric fan. This is installed in the
outlet from the chamber and thus draws samples through the system via pipe-work connected to
the chamber.
The ESU fan and gas detector must be connected to a Crowcon Gasmaster or Vortex control
panel, which will monitor the fan to ensure a sample is being drawn and display the gas level and
activate alarms. Wiring diagrams are shown on page 2 of this manual.
The sampling chamber is made from high impact ABS, and houses a gas detector with its junction
box on the outside. Connection points for the electrical supply to the fan are also made externally
to the sampling chamber via a second junction box.
2. INSTALLATION
One or two Xgard gas detectors can be fitted to the ESU. Refer to the General Arrangement
diagram on page 5 for details of how to fit the detector. A second detector (if used) is mounted at
the bottom of the enclosure.
The standard arrangement is for the sampling chamber to be fitted with 3 metres of PVC pipe on
either side of a T piece at the gas entry point to the chamber. It is possible to extend this to 6
metres, or to put the chamber at one end of a 12 metre length of sampling pipe. The attached chart
shows that with 12 metres of straight pipe, the minimum flow rate is 0.4 metres/sec which ensures
detector response in 60 seconds at most (including the T90 response time of the sensor). Any
extra bends or T pieces count as 2 metres of pipe. Other options are available, for example the
pipe-work can be closed at both ends with a series of small inlet holes along its length, or it can be
mounted vertically with a series of sampling holes along its length but with the bottom open for
immersing in liquid of varying depth. The sampling chamber should always be mounted above the
surface of any liquids to avoid ingress of water.
Because of the very low pressure developed by the unit, care must be taken with siting pipes to
ensure that extraneous pressure effects are eliminated, particularly in regard to wind and thermal
currents with open-ended pipes.
For wet well installations Crowcon recommend that holes are drilled every 500 mm (19.7”) in a
vertical plane from the bottom of the open-ended pipe. To ensure that airflow is always drawn from
the lowest level when the end of the pipe is submerged, the holes should be larger at the bottom,
gradually reducing in diameter towards the top of the pipe. As a general rule, the lowest hole
should be 6mm (1/4”) in diameter, reducing by 1mm (1/25”) per hole towards the top of the pipe.
These figures are dependent on the total length of the pipe, and should be adjusted as necessary.
