overload.
(_b_) Apparatus not requiring pressure regulators must be so
arranged that the gas pressure cannot exceed sixty-tenths (6) inches
water column.
This requires the use of the pressure relief provided for in Rule No. 20
(_a_).
(_c_) Apparatus requiring pressure regulators must be so arranged
that the gas pressure cannot exceed three pounds to the square inch.
The pressure limit of 3 pounds is taken since that is the pressure
corresponding to a water column about 6 feet high, which is about, the
limit in point of convenience for water-sealed reliefs.
22. AIR MIXTURES.--Generators must be so arranged as to contain the
minimum amount of air when first started or recharged, and no device or
attachment facilitating or permitting mixture of air with the gas prior
to consumption, except at the burners, shall be allowed.
Owing to the explosive properties of acetylene mixed with air, machines
must be so designed that such mixtures are impossible.
23. PURIFIERS.--(_a_) Must be constructed of galvanised iron or
steel not less than No. 24 U.S. Standard gauge in thickness.
(_b_) Where installed, purifiers must conform to the general rules
for the construction of other acetylene apparatus and allow the free
passage of gas.
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