4.2
The general schematic for a hazardous area purge system is shown in Figure 4.1.
WARNINGS (FIGURE 4.1)
1. If this component is mounted in a hazardous area it should be protected
by one of the norms listed in EN 50014.
2. Cable glands used in EEx 'd' apparatus shall be approved Ex 'd'
components, which maintain the degree of protection necessary.
3. All cable glands for use in electrical cable entries shall be of a type, which
seals and clamps the cable.
NOTES (FIGURE 4.1)
1. The PCS shall include an automatic device, which operates when the
overpressure falls below the minimum prescribed value. This device operates
in turn a pressure switch, which can be used for alarm and/or isolation
purposes.
2. Where the PCS is used to protect the 2500 bench unit only, the protective gas
supply shall be connected from the PCS to the 2500. The minimum level of
overpressure shall be monitored at or close to the outlet aperture of the 2500.
The maximum level of overpressure shall be monitored at or close to the inlet
and the PCS shall incorporate a limiting device to ensure that the maximum
overpressure specified in normal service (80 mBar) is not exceeded.
3. A protective device shall be fitted to the purge exhaust aperture to prevent
sparks or incandescent particles from being ejected from the pressurised
enclosure.
4. The PCS shall require to be put through a purge cycle after a pressure loss
before power can be restored to the instrument.
5. The PCS shall contain a pressure sensing element which is factory set, to a
level not less than the specified minimum (50 Pa, 0.5 Mb) and shall measure
pressure at the point in the system where the lowest pressure occurs.
6. The PCS shall supply a flow rate of protective gas, not less than 10 SLPM, and
shall incorporate an automatic device to monitor flow during the purge time
specified below.
7. The PCS shall maintain the minimum specified overpressure during the purge
phase and afterwards.
8. The PCS shall incorporate a purge timer, which shall be set to not less than
16 minutes. The purge timer shall be set to zero if either the minimum
overpressure or minimum purge flow is not maintained.
9. The PCS shall incorporate a device to ensure that power is not connected to
the apparatus being protected until the specified purge time has elapsed.
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