The safety tap differs somewhat from the ordinary tap, a section is
seen in figs. 6 and 7; the plug is hollow and forms the nose or spout
itself, this plug is only perforated on one side, so that it has to
be turned round half-way instead of quarter-way as in the common tap.
The upper part of the cylinder has an opening (of different shapes)
leading to the top of the plug, &c., a key being made to fit it (fig.
9). The American wooden taps (fig. 8), are just like it, but have
the handle united instead of a key. The four-way tap is a clever
contrivance for uniting four passages in alternate pairs; figs. 10
and 11 indicate the different positions of the plug. This kind of tap
was formerly an important part of the steam-engine, and allowed the
steam alternately to enter above and below the piston.