PROPELLING MACHINERY

and then, in succession, through the high pressure piston valve and high
pressure cylinder, intermediate pressure slide valve and intermediate
cylinder, low pressure slide valve and low pressure cylinder, doing work
on the piston of each cylinder as it expands. The slide valves admit
steam alternately above and below the piston. The steam then passes

Fig. 32.—Reciprocating Compound Engine*
into the condenser where it is condensed by coming into contact with
pipes through which cold sea water is being circulated. The air pump
extracts air and water from the condenser and passes the water into a
feed tank and from thence it is pumped back into the boiler.
The sea water runs into the condenser through an injection pipe low
down on the bilge, the circulation being maintained by a circulating