Report on Miscellaneous Implements at Shrewsbury, Sfc. 35 
near the bottom of its stroke, however, it uncovers a small hole which 
allows water from the hot-well to flow back into the plunger and over its 
«dges, thus forming a water seal. At the high speed at which these engines 
are run, a plunger, wholly submerged, would splash the water about too 
much ; but the contrivance we have just described avoids this trouble, and 
serves the same purpose of making a water-joint. In the engines exhibited 
the air-pumps are fitted with metal valves, the suction valve having a stem 
which projects through a bar on the delivery valve, and is furnished with a 
collar. By this arrangement the two valves are linked together, and as the 
outside diameter of the suction valve is slightly less than that of the hole 
which the delivery valve covers, the two valves can, when the vacuum is 
destroyed, be easily lifted out together by taking hold of a ring. 
Fig. 13. — Plan of Messrs. Eawfliorn, Daveij and Go's Domestic 
Motor. 
The boiler is fed from a closed feed chamber which is cast on the side of 
the condenser above the hot-well. This chamber is in free communication 
with the boiler by two passages, namely, a large one leading into the steam 
space, and a small one leading to the boiler below the water line. The water 
thus stands in the feed-chamber at the same level as in the boiler. The feed- 
water is brought to the feed-chamber by a flexible pipe attached to the cock, 
which has a nozzle projecting into the feed-chamber, the nozzle being fitted 
with a plug and float. If the water-level falls, the float of coiurse falls with 
it, thus lowering the plug and admitting more water to the boiler until the 
proper level is restored. In the case of the engines at Shrewsbury this arrange- 
ment worked admirably, the water-level being maintained with great steadi- 
ness, notwithstanding that there was a great fluctuation in the pressure in the 
mains from which the supply was drawn. 
The boiler is provided with a loose cover or large valve at the top, and when 
starting the engine steam is got up until it blows through this valve and 
€xpels the air from the boiler. The engine being then turned round and the 
condenser blown through, a partial vacuum is formed on the injection being 
turned on, and the engine works just like an ordinary condensing engine. In 
practice the engine does best if the steam is kept just below blowing-ofif point 
or practically at atmospheric pressure, as there is then no tendency for air to 
leak in at the stuffing-boxes of the piston-rod and valve-spindle, even if these 
are but slackly packed. The engine will, however, work perfectly well with 
D 2 
