PROGRESS IN TURBINE SHIP PROPULSION. 69 



larly find a place on war vessels which are required to operate for long periods at 

 different speeds, where there is a widely varying ratio of steam used by the auxil- 

 iary machinery to that used by the main turbines. In merchant vessels this ratio 

 is more nearly constant, but nevertheless careful study to the end of obtaining a 

 complete heat balance will be advantageous. Details of the two forms of valves 

 above described are shown in Fig. 8, Plate 35, and Fig. 9, Plate 36. 



The valve shown in Fig. 8 is intended for cases where there is never a defi- 

 ciency of auxiliary exhaust steam for feed heating. It comprises a piston having 

 atmospheric pressure above it, and the auxiliary exhaust steam below. When the 

 auxiliary exhaust steam pressure rises a sufficient amount above the pressure of the 

 atmosphere to raise the piston, steam may pass to the turbine. Air leakage into 

 the turbine is entirely precluded by ample steam seal around the piston furnished by 

 the auxiliary exhaust steam. The piston may be loaded to any feed heater pressure 

 desired. The upper cylinder is to forcibly close the valve in the event of the tur- 

 bine over-speeding. 



The modification of this valve shown in Fig. 9 is adaptable where there is 

 at times a deficiency of auxiliary exhaust steam. Any time the stage pressure 

 in the turbine is greater than that in the heater, the lower piston will rise, permit- 

 ting passage of steam from the turbine to the heater, at the same time, when re- 

 quired, permitting flow to the turbine as in the case of the valve shown in Fig. 9. 



It sometimes occurs that the turbine is subjected to such overloads that a stage 

 of the turbine selected to give the desired heater pressure at moderate loads would 

 be far too high for the heater at overloads. In this instance the modification 

 shown in Fig. 10, Plate 37, may be employed which limits the pressure in the heat- 

 ing system in accordance with the spring adjustment regardless of how high the 

 pressure may be in the turbine. 



It is the universal practice to employ closed tubular heaters in marine work, 

 while in land work what is known as the open heater is the rule. With the ad- 

 vent of turbine-driven auxiliaries and electrically operated winches, etc., the aux- 

 iliary exhaust may be uncontaminated with oil, permitting the employment of an 

 open heater for shipboard use, and a more complete separation of air from the 

 feed water. As this type of heater contains no tubes, the heating steam mixes 

 with the feed water, as in a jet condenser, so its cost is materially less. Frequently 

 these heaters are open to the atmosphere, and hence their name, but when working 

 in connection with the heat balance system they must obviously have no open out- 

 let, merely a provision for the separation of air, and a relief valve for safety. 

 Such a type of feed heater eliminates need of a separate feed tank and must be 

 located some feet above the feed pumps to preclude the latter being vapor bound be- 

 cause of pumping water near the temperature of evaporation. 



STEAM PRESSURES. 



The attention of central station engineers at the present time is being directed 

 to employing higher boiler pressures, viz., pressures as high as 600 pounds. To-day 



