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Zoe thought might possibly arise in the control mechanism first installed, al- though the latter has never developed any of the difficulties which it is pos- sible to conceive might arise. In 'prin- ciple the control is much the same as previously described in Engineering, though some of the parts have been eliminated, and the apparatus much simplified. The medium used for transmitting to the engine room the movements of the control handle on the bridge, is air, as previously employed, and the actual operation of the relays moving the steam valve, is oil. A diagrammatic arrangement of the operating parts of the control system, including the bridge valve and steam nozzle valves, is shown in Fig. 1. As will be seen' from examining the left- hand part of the illustration, the bridge control lever D' is movable in two quadrants A' and C' with an offset B' parallel to the axis of movement. When the control lever D' is at B' both the ahead and astern nozzles are closed. The operating handle D' turns a shaft carrying a cam £&' which has pressed against it the point of a small valve F'. The valve F' is hollow and closed at both ends, and has two sets of ports, G' and H', the former always being in communication with the source of high pressure air supply (furnished by a standard Westinghouse air brake compressor), and the latter having its edge to the extreme left, just line in line with the ports J' in the piston L'. The end of the plunger valev F' is line in line with left-hand edge of the ports I'. A small spring K' within the piston L' is provided to maintain a positive contact between the point of the plunger F' and the cam £', thus fixing the posi- tion of the plunger F' by its point of contact with the cam E'. The move- ment of the piston L' to the left is re- sisted by the spring N'. The space J' to the right of the piston L' com- municates with space: Q' between two diaphragms KR' R' and the space to the left of the piston L' communicates with the atmosphere. A communication to the passage within the piston L' to atmosphere is provided by the ports M'. The diaphragms R' R' control two valves T' and U', the former controlling an opening to atmosphere, and the latter an opening to the source of high pres- sure air supply. The spaces S' S$' are connected by a passage, so that the pressure in them is always equal. The space S'communicates either with the ahead or 'the astern operating relay in the engine 'room. The function of the. bridge control valve just described is 'sinply to main- tain a predetermined constant pressure in the air relay cylinder, and this is THE MARINE REVIEW accomplished as follows, with the .ap- paratus just described: When the lever D' is moved from its central position, B'in the ahead quadrant A', the cam E' pushes the valve F' to the left, thereby bringing the port H' into communication with the port /' in the piston L'. This admits high pressure air into the space J', and consequently Q'. As the pressure in the space J" increases it will quickly force the piston tO the left, until the right-hand edge of the port J' cuts off communication with the port H', or should there be leakage, it - will take a position such that the open- ing through ports H' and J' would be just large enough to pass sufficient air to make up for the leakage and main- tain a constant pressure in the space J'. Since normally the spaces S' S" are at atmospheric pressure, when the pres- Procol Ni Ny sete NY = i / N 1 id U bet Kanbidbddddddddddddiddéél A] dS SSS June, 1914 Rk' R' will be distended slightly, thus holding the valve U' open sufficiently to make up the leakage and maintain con- stant pressure. Conversely, it is eyj- dent that if the pressure in the space J' should increase above that predeter- mined for a given position of the piston F', the piston L' wall move to the left, and open communiéation between the space J' and. the inside of the piston 1 thus exhausting air from the space J' to atmosphere through the port M'. This condition also arises when operating lever D' is moved towards the off or central position, which permits. the movement of the valve F' to the right. In the latter case the pressure in the space Q' will be decreased and become less than the pres- sure in the spaces S" S"', causing the diaphragms R' RF' to collapse and open the valve 7' to atmosphere until the CN ANG GS re WS yy VW ZL ah) b ZZ SA PL re SS SSS YZ CC WMSS&XXXTE E Y HH Y= Ni i RN commer) | ame SS ZL) Pe NIE RN FIG. 1--DIAGRAMMATIC -ARRANGEMEN1 OF BRIDGE CONTROL AND NOZZLE OT Ciccccccccae pte od Va a ee ea MU Ml Y SD \ iY ars | Ki ee LY swim, mY Gail Gal Ga ccccciccccceaaaaaquaaa LA Yj ae : yj oT WAKES = y Y Yj 4 f Ci gddddddddddddada VALVES sure between them in the space Q' is increased, the diaphragms are forced outwards, closing the valve T' and open- ing the valve U', thus admitting high pressute air into the space S' S$' until the pressure in the latter is equalized with the pressure in the space Q', thus bringing the diaphragms back to their normal position, permitting the valve U' to seat and thus cut off the supply of high pressure air. The pressure existing in the space §" is transmitted fo the space P to: the left of the air relay cylinder in the engine room. As in the case with the piston L' and the ports J' and H', should there be leakage in the piping system communi- cating with the space S$', the diaphragms pressure in the spaces S"' S' is decreased to that in the space Q". When the control lever D' is to be moved to the astern position, it is neces- sary to move it in the direction of its axis of rotation in the slot B'. When this is done, an arm W', held' between two collars on the cam shaft, moves the small slide valve X' to the right, and bridges the pipe Z' to the astern air relay cylinder into communication with Space S', and the pipe 2" into com- munication with the atmospheric eX- haust. From the above it will be seen that it is impossible for the operator to be- come confused and accidentally move the control lever in the wrong direction, WLLLLLLLLLLLULLLULLELL ELLs NY NY CZ, Bog hark at gk Ge eae na CE I GE a aa aoe dd oe