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The E-T Air-Brake Pocket-Book
valve, and the emergency slide-valve, to assume the same positions as represented in Fig. 19, but by the time the brake-pipe air is so far exhausted as that, the brake-cylinder pressure in passage m and the checkvalve chamber will be equal to it, or greater, and check valve 53 can not be unseated. To secure full emergency action, the application must be made with brake cylinders (previously) empty; partial emergency is obtainable only so long as the brake-pipe pressure is appreciably greater than that in the brake cylinders; but after a service reduction of as much as 15 pounds, no quickaction results may be expected.
THE E-6 SAFETY VALVE.
USED ON THE No. 6 DISTRIBUTING VALVE.
Fig. 20 is an enlarged sectional view of the E-6 SAFETY VALVE that has been shown attached to the distributing valve in each of the preceding colored charts of the No. 6 E-T equipment. It is a quick-closing valve seating with a "pop" action, unlike the ordinary safety valves, is sensitive in operation and responds to slight differences in pressure.
The names of the parts of the safety valve are: 2, BODY; 3, CAP NUT; 4, VALVE; 5, VALVE STEM; 6, ADJUSTING SPRING; 7, ADJUSTING Nut. In each of the distributing-valve charts a STRAINER, 43, is seen just under the safety valve, and this piece should be included in the parts, although not appearing in the individual plate, Fig. 20; its use is essential, to prevent loose scale or other matter from being carried to the safety valve and lodging on the seat to make a leak that would result in the loss of brake-cylinder pressure.
The valve, 4, is cylindrical in form, fitting neatly in the surrounding bush which acts as a guide, and is held to its seat by the compression of spring 6 between the shoulder of the valve stem and adjusting nut 7. When the air pressure beneath valve 4 becomes greater than the resistance of the spring, the valve raises from
The E-T Air-Brake Pocket Book
Copyright, 1909, by The Norman W. Henley Publishing Co.
Fig. 20.-E-6 Safety Valve. Used on the No. 6 distributing valve.
its seat and then exposes a larger area to the air pressure which quickens its upward movement and prevents the valve from “chattering" on its seat.
Two ports are drilled in the valve bush upward to the spring chamber; and two are drilled outward through the bush and valve body to the atmosphere, although but one of each of these is shown in the cut. The lift of the valve is determined by the stem, 5, striking cap nut 3, when it closes the two vertical ports in the bush connecting the valve chamber and spring chamber, and opens the two lower ports to the atmosphere; as the exhausting pressure of the air below the valve becomes less than the pressure of the spring, the latter forces the stem and valve downward, during the movement of which the valve restricts the lower ports to the atmosphere and opens those between the valve and spring chambers, and the discharging air pressure then has access to the spring chamber; this chamber is always connected to the atmosphere by two small holes through the body, 2, and the air from the valve chamber, entering more rapidly than it can escape through these holes, causes pressure to accumulate above the valve and assist the spring to close it with the "pop" action before mentioned.
This safety valve used in connection with the No. 6 distributing valve should be adjusted for 68 pounds; this is done by removing cap nut 3 and screwing
Care of Safety Valve
adjusting nut 7 down to raise, or up to lower, the pressure, and after the proper adjustment is made cap nut 3 must be replaced and securely tightened, and tested by operating with pressure a few times. The adjustment is more easily and accurately done on a shop testing rack.
The safety valve requires some attention and care. Particularly, it must be seen to that the holes in the valve body are always open, but they must not be reamed out by those who erroneously imagine that the capacity for pressure discharge should be increased especially as to the two upper holes.
Occasionally the safety valve should be removed from the distributing valve, the strainer taken out and cleaned and the air passage that leads to the safety valve blown out by placing the independent brakevalve in application position. The safety valve should be taken to a bench and cleaned; remove the cap
and adjusting nuts, the spring and stem; then invert the body and shake out the valve, 4, being careful that it shall fall on nothing hard that may dent or burr it; clean the inside of the body and the several holes referred to, and the valve bush; clean the valve, and rub a thin film of graphite air-brake and triple-valve grease around its sides and on the valve bush; replace everything, readjust to the correct pressure as before explained, reattach the safety valve to the distributing valve, and test.