Richardson's Combined Pressure and Vacuum Relief Fake is shown in Fig. 7. This valve is designed to be placed in the steam chest of locomotives to automatically supply to the cylinders, through the air valve, A, when the engine is running with steam shut off, a free supply of air from the outside instead from the smoke-box, laden with hot gases and cinders. The pressure relief valve, B. performs the function of preventing the dangerous accumulation of pressure in the steam chest and dry-pipe when the engine is suddenly reversed.
The ..ifason Reducing Valve ig shown in Fig. 8. In this device an auxiliary valve, con trolled by the low pressure, admits steam from the high-pressure side to actuate the main valve, which is a differential piston. The high-pressure steam enters the reducing valve at the side marked A. and passing through the auxiliary valve, if, which is held open by the tension of the spring, S, passes down the port marked " from auxiliary to cylinder," underneath the differential piston, D. By raising this piston, D, the valve, C, is opened against the initial pressure, since the area of C is only one-half of that of D. Steam is thus admitted to the low-pressure side, and also passes up the port, _V X. underneath the dia phragm, 0 0, upon which bears the spring, S. When the low pressure in the system has risen to the required point which is determined by the tension of the spring, S. the dia phragm is forced upward by the steam in the chamber, 0 0, the valve, h, closes, and no more steam is admitted under the piston. D. The valve. C, is forced to its seat by the initial pressure, thus shutting off steam from the low-pressure side. This action is repeated as often as the low pressure drops below the required amount. This piston, 13, is fitted with a dash-pot, le, which prevents chattering or pounding when the high or low pressure suddenly changes.
Locke's Renewable-disk Check Valve is shown in Fig. 0. The ordinary form of check valves used in boiler feeding are liable to become leaky by being beaten out by the " water hammer," caused by the stroke of the pump. In this valve it is sought to avoid this trouble by employing a soft, renewable disk in the form of a truck (as shown in the cut), and constructing the seat of the valve with sufficient bearing surface to prevent the soft packing from having its surface ruptured by hammering on the metal seat of the valve. This is
done by constructing the valve seat, with arms radiating from the center, thereby supporting the packing at the center and at all points from the center to the circumference. A water cushion is thus funned. which prevents the contact of the packing with the metal seat ; the valve really cushioning upon water, as the water has to be forced out before the parts can rest on each other.
The Thomson Faucet.—The faucet represented in Fig. 10 has recently been devised by Sir William Thomson. ]t is made entirely of metal. The metal valve, A, on reaching the seat, B. also of metal, is not suddenly arrested and compelled to seat itself haphazardly, hut con tinues to turn on its seat as the }handle is turned, receiving meanwhile a gradually increasing pressure from the spring, C (non-corrosive). centrally applied by the rounded head of the stop. D. The valve is thus rubbed upon its seat at every opening and closing, and both valve and seat acquire and maintain a perfect fit and finish. The manufacturers state that no material wear is shown on the valve and seat, even after it has been opened and closed as much as would occur in many years' service. The spiral spring has been subjected to com pression 700,000 times without showing any loss in power. The cock has been opened and closed by machinery, with water flowing, 540,000 times, or the equivalent of 50 years' use at 30 times a clay. At the end of the test. the valve was still tight. The method adopted to avoid the use of the ordinary stuffing-box is very ingenions. An " eduction tube," F, pro jects into the faucet opening, and sucks out any water which may collect in the chamber around the valve stem through leakage around the screw when the valve is opened. This device is claimed to be thoroughly effective.
(See Govmmotts : ENGINES, STEAM ; and REGULATORS.) Tanner : see Ore-dressing Machinery.
Vats : see Mills. Silver.