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MODERN STEAM PRACTICE.

tightening up the packing rings, which is done by means of abox Spanner inserted through the hole, taking a square part onthe screwed studs, which, being turned in a particular way, causesthe ratchet to click. Thus the engineer, by counting the numberof clicks for each set bolt, can set up the faces equally. It isadvisable that the rings should be tightened up under steam, so asto adjust the faces for the expansion of the metals. This plan isneat, but many engineers consider it not nearly so efifective as theusual method with plain set screws, packing rings, and plaitedgasket, as before described.

To enter into details of an arrangement for taking the pressure offthe back of the slide valve, with a piston having an oscillating link,&c., would be of little practical benefit, as such has been very rarelyadopted. Suffice it to say, that the piston works in a short pipeaccurately bored out, and placed or cast in the valve-casing cover,having a link for connecting the valve; the steam pressure acting onthe piston tends to pull the slide-valve from the face. Thus theforce is suspended, as it were, on the link pin, and consequentlythe valve is more easily moved. Sometimes a piston has been intro-duced to balance the weight of the slide-valve when placed verti-cally, and no doubt the plan is good when the slide-valve is verylarge, as the strain on the valve gear is not so much feit. Thepiston should be fitted with small Steel spring rings, thus simplify-ing the arrangement

THE INDICATOR DIAGRAM.

When the steam in the cylinder is cut off at any part of thestroke of the piston, and were no condensation taking place, the pres-sure of the steam at the end of the stroke, or at any intermediateportion of it, could be calculated to a nicety. The curved line thatwould delineate the steam pressure inside of the cylinder from thepoint of cut-off would then be quite regulär. But in practice thereare various causes that tend to make the line of expansion a veryirregulär figure; for instance, with a slow cut-off, as with the eccen-tric motion, the line of expansion does not approach so nearly the