They require the collar on the internal pipe of the joint (on which the gland fits) to be permanently fixed by soldering or brazing, and check nuts on the studs, so that the internal pipe shall not be blown out from the steam pressure.
This pipe is also sometimes fitted with chains or stops, in case the studs should break, or the nuts or collar strip.
An oil cup is either a cavity cast in the piece or a cup shaped vessel or hollow cylinder screwed in. It contains a pipe extending up about three-fourths of its height, and through this pipe the oil is fed to the surface required to be lubricated. A hinged lid or, in some cases, a screwed cap covers the oil cup to exclude dust, etc.
The syphon or worsted consists of a number of threads of worsted or lamp wick of equal lengths; a piece of lead or copper wire is laid across the middle of the worsted, the copper wire is doubled and twisted and is then pushed down the tube, carrying the doubled end of the worsted with it. The upper ends of the wire are bent over the end of the tube so as to hold the worsted, whose lower end should pass down below the level of the bottom of the oil cup. The oil feeds (on the syphon principle) through the medium of the wick or worsted, which should not fit the tube tight but quite easily, its upper ends hanging over the top of the tube to the bottom of the cup.
The worsted may be cleaned with scalding water, or by water thrown upon it from the boiler.
Tallow cups for high pressure cylinders must have two cocks, so that after the cup is filled the top cock may be closed and the bottom one then opened. The top cock prevents the tallow or oil from being blown out of the cock by the steam. For the low pressure cylinder a cup with a single cock will answer, as the cock may be opened when the vacuum is at that end of the cylinder, and the air will force the oil or tallow in.
A steam lubricator or impermeator is an automatic oil feeding device placed on the steam pipe of the high pressure cylinder. Steam lubricators are made in various forms, some having a positive feed by a pumping arrangement, while in others the oil floats upon water in the body of the lubricator to which steam is admitted; the condensation of the steam increases the quantity of water and causes the floating oil to overflow and feed through a pipe leading into the steam pipe or steam chest, as the case may be. Cooling the impermeator causes more rapid condensation, and increases the amount of oil fed to the steam.
Cylinder escape or relief valves do not let all the water out of the cylinder because of the clearance,[59] hence the amount of water left in will equal the amount of clearance.
[59] See [page 372], on clearance.
The small cylinders on top of the steam chest are for the purpose of guiding the upper ends of the valve spindles, and are fitted with pistons having steam beneath, the upper end being in communication with the condenser.