8 4

MODERN 3TEAM PRACTICE.

the superheater. One stop-valve is fitted to the superheater forregulating the steam to the cylinders, while in connection with thisstop-valve and pipe there is fitted a stop-valve on each boiler,having a pipe connected to the main steam-pipe, thus in the eventof anything going wrong with the superheating apparatus, all thestop-valves connected to the superheater can be closed, and thesteam taken from the boiler in the usual manner. This will showhow much more preferable it is to form high steam-chests and up-takes; thus complication is reduced to the minimum, while at thesame time the steam is effectively dried. Superheaters, in all caseswhen made separate vessels from the boiler, should be fitted with asafety-valve, of ample size; this is to prevent rupture, as, in case allthe stop-valves are shut, a certain amount of moisture, or evensteam, is in the superheater when the valves are closed, and thiswould generate a highly-explosive dry gas, or steam proper, were thesafety-valve not relieving the superheater from the accumulatingpressure. In the absence of steam in the superheating vessels, theinjurious effect of the waste heat passing up the chimney actingupon the dry plates and small tubes need scarcely be pointed out.

In concluding this brief sketch of superheaters, that have all beenpractically tried more or less, it may be stated that for pressures oi60 lbs. per square inch in the boilers the simplest arrangement thatis found in practice to suit all requirements is a circular shell fittedwith an internal flue. The surface exposed, or total surface of theinternal flues, in this System is i'3 square foot for every nominalhorse-power the engine is calculated for; but for low-pressure steamthe surface is generally i square foot for every indicated horse-powerthe engine works to; or otherwise from 3 to 4 feet square per nominalhorse-power is reckoned amply sufficient for the superheating sur-face, as usually arranged, for pressures varying from 20 lbs. to 30 lbs.steam in the boiler.

We will now consider the different points to be attended to in thearrangement for conveying the steam from the boiler to the cylinder.With the view of keeping the steam as free as possible from wateryparticles, as has already been discussed in the section on priming,a pipe is fixed to the interior of the boiler, perforated throughoutits length with a number of holes, by which the steam is removedfrom over the parts where it is rapidly generated. This pipe shouldbe fitted to all boilers, whether using superheaters or fitted withordinary arrangements. The use of the Separator has also been