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| Ventilatory Products
>> Air Receivers |
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Important though after coolers
are, it would be very unusual for all the water vapour in the air to condense
at this point. Further cooling almost always takes place in the receiver
as well as from the distribution system. The water vapour, (and oil mist,
if the compressor is of the lubricated type) condenses in the receiver and
collects at the bottom. On those installations where the compressor plant
is small, an after cooler may not be fitted, thus making the receiver the
point at which most condensed liquid will be found. If these liquids are
allowed to build up, carryover into the mains system is likely. There is
also the possible corrosion of the receiver itself.
It is, therefore, important to ensure that these collected liquids and solids
(atmospheric dust, pipe scale, carbon, rust, etc) are automatically removed
as they collect. Fig. 10 shows a typical vertical receiver: 1 and 2 show
alternative positions normally found for the discharge pipe. As the trap
and its protective strainer will have to handle varying proportions of water,
oil, emulsion, dirt, etc, regular cleaning is essential. If excessive amounts
of oil are being carried over from the compressor (generally indicating
that maintenance of the compressor is required), the system shown in Fig.
11 may be found effective. A manual drain cock is fitted to the receiver
a short distance up from the drain trap outlet. Oil and scum floating on
the water surface (which might foul up the trap) can be periodically drained
off. |
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Apart from the receiver's ability
to cool the air and hence deposit liquid (that is why it is better to site
the receiver where the ambient temperature is low), it performs two other
functions. For some applications, it is important that the pressure pulses
produced by a reciprocating compressor be eliminated as far as possible.
The receiver, therefore, acts as a pulsation damper. The receiver also acts
as a power storage vessel, allowing intermittent high demands for compressed
air to be met from a smaller compressor set.
Being a pressure vessel and thus subject to regular inspection, a receiver
is fitted with inspection covers or man-holes. These also allow any solid
contaminant build-up to be removed. To comply with the factory and safety
acts a receiver must be fitted with an adequately sized safety valve and
generally a pressure gauge is also fitted. |
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