Improvements in and relating to Steam Superheaters

108,690. Parsons, Sir C. A., and Cook, S. S. May 13, 1916. Overheating of superheating - tubes, preventing. - A superheater is provided at its outlet end with a relief-valve adapted to blow off at a lower pressure than the boiler safety-valve. The pressure at which the reliefvalve blows off may be adjusted automatically by a thermostat in the superheater or by a pressure-operated device. The relief-valve 1, Fig. 4, is controlled by a thermostat consisting of concentric alternate steel and copper alloy tubes 5, 6 placed in an enlarged superheatertube 3. An increase in the steam temperature causes the valve-spring cap 10 to lift, and so reduces the spring pressure and the blow-off pressure of the valve. In modifications, the lever 13 engages a sliding piece between two springs on the valve spindle, or engages the spindle directly. A thermostat 21, Fig. 6, placed between the superheating-tubes consists of a flat bar of alloy riveted at one end to the free end of a double bar, which is slidably supported on a bracket 36. The thermostat operates a relay valve 23 controlling the supply of steam through a pipe 27 to a chamber 28 containing an enlargement of the valve spindle 30, the steam pressure acting on the enlargement in opposition to the pressure of the spring. A relief-valve may be connected by a pipe to a highpressure steam space of the main engines, the steam pressure acting on an enlarged part of the valve. The relief-valve 51, Fig. 9, is controlled by the drop of pressure of the steam in passing through the superheater, which drop varies with the quantity of steam passing. Steam from the superheater inlet is led by a pipe 55 to a chamber 54 containing a piston 53 on the valve spindle and forces the relief valve on its seat against the upward pressure of a spring 57 and of the superheated steam acting on the face of the valve. The pressure drop through the superheater may be increased by restrictions in the inlet or ontlet pipe, or by a valve 59 having a weak closing spring.