LOCOMOTIVE ENGINE. 
449 
the cock turning round for the purpose. An oil cup is shown one quarter the full 
size in figs. 26, 27, and 28. Fig. 26 is a side elevation Fig. 26. fig. 27. 
of it; fig. 27, a section through the centre; and fig. 28, 
a plan of the top. The cup A is made of brass, and 
the cover B has a piece projecting from it turning upon a 
pin in a socket C at the side of the cup A, and square at 
the end, resting upon a small spring at the bottom of the 
socket to hold it either open or shut. An iron tube D, 
is fixed into the foot of the cup, extending to the top, and 
projecting through the bottom, where it is screwed, for 
the purpose of fixing the cup on to the part which has to 
be oiled. The hole into which the cup is screwed runs through to the rub 
bing surface; and some cotton thread is put through the tube, dipping into the 
oil in the cup, and the other end touching the moving part; the thread acts as 
a syphon, and continually drops the oil upon the rubbing surface. The oil cups 
were made at first without the tube or cotton thread, but the oil was found to run 
out too quickly, and could not be kept supplied; loose cotton was then put into 
the cup to prevent the oil running out so fast, but the syphon cup acts much better 
as it supplies the oil uniformly and gradually. The oil cup on the crank end of the 
connecting rod has so violent a motion, that it is almost impossible to keep the cover 
shut without the spring is very strong; the covers are sometimes detached and screwed 
on, but they are then very liable to be lost; and the best cup for that purpose is one 
without a loose cover, but with only a small hole in the top to pour in the oil, and 
made funnel-shape inside to prevent the oil jolting out of the hole. 
The faces of the slide valves and the outside piston rings are subject to considerable 
wear, from the pressure upon them and the rapidity of their motion; but the wear is 
very much increased when the boiler is supplied with dirty water, priming much 
in consequence; as the water which gets over into the cylinder carries particles of 
sand with it, which grind the rubbing faces very quickly. The slides in the engine 
shewn in the engravings have just been removed, having lasted two years ; the old 
ones were worn down to less than a quarter of an inch thickness of flanch. The 
piston rings are not yet worn out; they usually last about three years. In another 
engine that had run upon a part of the works where the water was very bad and 
sandy, the piston rings were worn down to one eighth of an inch thick in four 
months. The cylinders get worn uneven in time by the friction of the pistons, and 
require reboring ; about one eighth of an inch is taken off by the boring, and they are 
bored out generally two or three times before they are worn out; they wear usually 
3 L 
Fig. 28.