Modern locomotive valves and valve gears by McShane Charles

Author:McShane, Charles
Language: eng
Format: epub
Tags: Locomotives
Publisher: Chicago, Ill., Griffin & Winters
Published: 1917-03-25T05:00:00+00:00

Fig. 48-valve, against which the auxiliary valve abuts. It will also be seen by inspection that the center exhaust passageways extending vertically through the center of the main and auxiliary valve are always in communication.

The auxiliary exhaust passages, which extend entirely through the body of the main valve, are positioned to register with the cylinder ports in the valve seat after

the inside edges of the main valve have passed inwardly beyond the ports, and delay compression by providing means of escape for the steam which would normally be trapped in the cylinder ahead of the advancing piston.

This is manifest by an inspection of the left-hand port shown in the illustration, for the point of exhaust has been reached in the right-hand port while exhaust continues in the left-hand port; in fact, the left-hand port will remain open for exhaust until J4 i^ch of the port opening for steam admission.

At the same time it will be seen that premature release in the right-hand port is prevented by the auxiliary valve closing the upper end of the vertical auxiliary passageway extending through the main valve, so as to prevent release until the inner edge of the main valve has moved to a position to open the right-hand cylinder port.

The auxiliary valve travels back and forth in the steam chest with, and in the same direction as, the main valve, as the latter approaches the end of its stroke.

The two valves are balanced in the usual manner by the use of springs, or other resilient means, interposed beneath packing strips which fit in grooves and are forced against the pressure plate, to produce a seal between the interior of the valves and the live steam compartment.

The main valve is lubricated by means of steam, trapped in a series of transverse grooves, or steam

pockets, cut in the valve face beneath the valve, as the latter slides thereover. The expansive force of the trapped steam in these pockets tends to raise the valve from its seat, thereby reducing friction and eliminating the necessity of artificial lubrication. In fact it is claimed that this system of lubrication permits the valve to be used with success on a high degree superheated engine.

It has been demonstrated that one of these double acting valves having i inch outside lap, and }i inch exhaust lap, will give 40% increase of expansion. With i inch outside lap, and exhaust line and line, however, a decrease of compression of about 75% over the plain slide valve, may be obtained.

A set of these valves have been in use on an engine of the Illinois Central Railroad Company for about three years, and so far neither the valve nor the valve seats have been refaced, nor has as much as a file been touched to them. The locomotive equipped with this valve shows a good coal and water record, leading all other engines of her class in similar service by a good percentage, but an official test has never been conducted, and therefore accurate data cannot be given.

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