12 6

MODERN STEAM PRACTICE.

inches.

The outside exhaust port on valve. 3%

The width of the narrow face on valve. 1%

The width of the inner steam port on valve. I %

The inside lap for steam port. iji

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Thus the valve and adjuncts can be delineated from the foregoingdimensions. The packing ring on the back should be as large in dia-meter as the length of the ports will admit of. The rubbing ring onthe back of the valve is of brass, while the one the set screws pressagainst is of wrought iron, a common gasket packing being inter-posed between the rings. Some have proposed springs along withthe packing, with the object of relieving the cylinder in case ofpriming. It need scarcely be stated that when springs are intro-duced they must be placed so that the set screws press them againstthe wrought-iron ring.

RELIEVING THE CYLINDER FROM INTERNAL PRESSURE.

With the desirable object of relieving the cylinder from internalpressure the author has arranged a species of valve differing mate-rially from the double-ported dass, having the rings on the backfor relieving the valve from back pressure. The arrangement pro-posed admits the steam from the boiler into the cylinder throughthe middle port cast on the cylinder, the valve-casing communicat-ing with the condenser. The steam by this plan has a tendency toblow the valve off the face, and to prevent this occurring the valve isprovided with a steel plate on the back, let into and securely attachedto the valve; rollers bear on this plate, fitted with journals andguide-rods, which pass through the back of the valve-chest cover,having suitable stuffing-boxes perfectly air-tight. There are curvedsprings secured with mid shackles to the valve-casing cover. Thesesprings have holes drilled at the ends, through which the spindlespass; the ends of the spindles are screwed and fitted with nuts, sothat by adjusting the springs any amount of pressure on the valveface can be obtained. It will be seen that, from the steam passingthrough the valve, the latter is very nearly in equilibrio; still thesteam has a tendency to blow the valve from the face. This iscounteracted by the rollers, which can be so adjusted as to throwback a little more than the outward pressure; thus the only pres-sure on the face of the valve is the difference between the outward