For many reasons, such as capacity for isolation when being recharged or
repaired, it is highly desirable that each item in an acetylene plant
shall be separated, or capable of separation, from its neighbours; and
this observation applies with great force to the holder and the
decomposing vessel of the generator. In all large plants each vessel
should be fitted with a stopcock at its inlet and, if necessary, one at
its outlet, being provided also with a by-pass so that it can be thrown
out of action without interfering with the rest of the installation. In
the best practice the more important vessels, such as the purifiers, will
be in duplicate, so that unpurified gas need not be passed into the
service while a solitary purifier is being charged afresh. In smaller
plants, where less skilled labour will probably be bestowed on the
apparatus, and where hand-worked cocks are likely to be neglected or
misused, some more, automatic arrangement for isolating each item is
desirable. There are two automatic devices which may be employed for the
purposes in view, the non-return valve and the water-seal. The non-return
valve is simply a mushroom or ball valve without handle, lifted off its
seat by gas passing from underneath whenever the pressure of the gas
exceeds the weight of the valve, but falling back on to its seat and
closing the pipe when the pressure decreases or when pressure above is
greater than that below.
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