general type the big shell casting is bolted to the guide yoke as well as the frame, and becomes a most substantial engine frame and valve-gear stiffener, but with another class of engines the casting referred to is separate from the guides yet carries the link, and as the American bar-frame is not altogether unyielding, this big, powerful freight engine will in time, no doubt, develop certain irregularities in the valve's action. that may be attributed by some to the fact that the engine is equipped with the Walschaert valve gear.

Q. 45. If an engine breaks any part of the machinery while on the road, is there any great difference in the method of disconnecting the disabled side and setting things right so as to proceed, as to whether the valve gear is of the Walschaert type or the Stephenson link motion?

A.-Yes; and if the break occurs within the valve gear the difference in time consumed in making the temporary repairs necessary to get the engine moving under its own steam is so greatly in favor of the Walschaert as to be one of the good reasons for its adoption, because it means less time lost in delays to the railroad's one source of revenue-the turning wheels.

When railway motive power was not so large and heavy as at present, and any part of the machinery on one side of an engine was broken so as to disable that side, it was the rule to take down the main rod

and block the valve after disconnecting the valve-stem; the main rod had to come down from one side, always, when the engine was only able to work steam on the other side. The piston was then held at the back end of the cylinder by blocking the crosshead, and the valve on that side was set so as to cover both steam ports by blocking it or clamping the valve-stem; not a great deal of knowledge or ingenuity was required; simply follow the custom.

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Now, however, the enormous weight of the main rod generally prohibits taking it down on the road; leaving it up in place suggests that the piston will 'drift" in the cylinder while the engine is running dead on that side, and that the crosshead will impart motion to the combination lever, et al. So that a few questions asked and answered on the subject of common breakdowns and the accidents that might happen to the parts of the Walschaert valve gear would be appropriate.

Q. 46. In discussing the subject of breakdowns and the methods of procedure in consequence, "blocking the valve" will be mentioned several times; what is meant by that expression, and when and how should it be done?

A.-When any part of the valve gear is disabled on one side of the engine so that the valve will not receive its correct motion, or if any other part of the machinery

on that side of the engine is in such a damaged condition that steam must not be delivered to the cylinder of that side while the engine is working on the other side, the gear must be disconnected so far on the disabled side that the valve shall not be disturbed, after which the valve must be placed in a central position on its seat, by moving the valve-stem, whereby both admission ports to the cylinder are covered. After the valve has been correctly centred, if the throttle is slightly opened no steam will blow from the opened cylinder cocks on the disabled side of the engine. The cylinder cock rigging should then be disconnected on the damaged side of the engine, so that they could be set permanently open while the engineer opened or closed the cocks on the other side without interference; one reason for doing this is that if the valve should get moved far enough to start uncovering one of the admission ports steam would blow from the cylinder cock at that end of the cylinder and announce the shift of the valve when the throttle was opened.

On many roads a clamp is furnished and carried on every engine, by which the valve-stem can be secured immovably in a position that places the valve squarely over the ports. When such clamp was not at hand, it was formerly the rule, with a D-slide valve, to raise the steam chest cover and place retaining blocks

ahead and back of the valve; but it is almost an impossible task to raise the steam chest cover' on one of our big, modern engines, and it is not at all unsafe to neglect the inside blocking; just centre the valve, and when steam is used it will put such a great weight upon the valve that its frictional resistance will cause it to adhere to the seat beyond any danger of its moving, unless the engine receives a hard bump as in switching or coupling to cars, and in that case the engineer will quickly discover the fact from seeing the steam at one of the cylinder cocks.

Inside admission piston valves are so perfectly balanced-fore and aft-that one need not hesitate to trust them to "stay put" without clamping; still, if there is a clamp provided, use it.

Some engineers with a high reputation for keeping the wheels turning in spite of mishaps, refuse to block the valve on the disabled side of the engine and they leave the main rod up, also; it is out of the question to take down, on the road, the heavy main rod that we now find on most engines, and if the engine subsequently stops with the live side on the dead centre, the disconnected valve can be temporarily moved far enough to open the desired steam port and enough steam then used to start the engine and get the working side off the centre; the air brake can then be applied to stop the engine with the live side off the

centre, and with the throttle closed the disconnected valve is again put on centre, and the train proceeds.

When the main rod is left up, the fixed-open cylinder cocks will generally give relief enough to prevent compression and vacuum in the cylinder as the piston churns forth and back, but for further relief some engineers always unscrew the cylinder cocks to provide an increased opening in each end of the cylinder. If the cylinder has by-pass valves they can be made to take care of the churning of the piston. The piston will run dry, however, and needs lubrication; oil must be introduced to the cylinder if the engine is to be run for any considerable distance. The lubricator may be allowed to feed oil to the steam chest on the broken-down side about the same as usual, and at certain stops along the road the valve can be moved by the valve-stem-if not blocked-enough to open one, or each alternately, of the admission ports and given a little steam, the oil collected in the steam chest will be blown down into the cylinder.

Q. 47. If a side rod breaks, or should otherwise be removed from the engine equipped with the Walschaert valve gear, and no other damage results to the machinery, could it have the effect of totally disabling the engine?

A.-No. The engine would still work all right on the uninjured side in all such cases.