72 PROGRESS IN TURBINE SHIP PROPULSION. 



sake of reliability that each oil pump alone be large enough for the system. These 

 pumps are relayed by an auxiliary steam-driven pump for use when maneuvering. 

 The direct-driven pumps have been objected to in some quarters and duplicate steam- 

 driven pumps substituted therefor. The advantage of the latter, while no doubt 

 lacking the extreme reliability of the direct driven pumps, is that, when properly 

 controlled, it need only pump the oil needed by the system instead of say three times 

 as much, which no doubt will have much to do with increasing the life of the oil 

 as well as simplifying the filtering or straining systems. What is regarded as an 

 ideal system is shown in Fig. 14, Plate 41. It has the following features: — 



1. The pumps are located at as low a level as possible to reduce the suction head 

 to the extreme limit. 



2. The drain tank is of as large a dimension as practicable, and is located suffi- 

 ciently low to insure the oil draining freely to it from the machinery with ample 

 sized pipes, and assurance that with the extreme rolling and pitching there will be 

 no leakage from the bearings. 



3. The pump suction should be several inches above the bottom of the tank to 

 avoid drawing dirt and emulsion from the bottom. 



4. It is regarded as desirable to employ an additional suction from the bottom 

 of the tank by means of which dirty oil may be pumped through a filter and to per- 

 mit complete emptying of the tank for cleaning purposes. 



5. The pump is arranged to discharge its oil through coolers to an overhead 

 gravity tank located some twenty feet above the machinery. 



6. Duplicate coolers are employed so that while one set is in use the other may 

 be cut out of service. They should be by-passed with a spring loaded check valve, 

 loaded to some amount greater than the resistance of the cooler so that under no 

 conditions can mishandling of the valves cause interruption to service. 



7. An overhead gravity tank is provided with three strainers having succes- 

 sively finer mesh. The photograph of one of these strainers is shown in Fig. 15, 

 Plate 42. The screens are successively of finer mesh, the first being sheet metal with 

 1/16 inch perforations, the second thirty-mesh wire gauze, the last seventy-mesh 

 wire gauze. In the event of these becoming choked there can be no interruption 

 to service, for the oil merely flows over the top, when they may be readily removed 

 for cleaning. The screens are secured to quite large cast frames arranged as 

 shown in Fig. 15, so that any dirt falling from the screen on their being removed 

 will be caught in the frames and thus removed. 



From these the oil passes through a fractional filter, that is, some of the oil runs 

 through filter bags and is thoroughly filtered, the rest overflowing. 



The gravity tank should be provided with a very rugged float of large power 

 for controlling the speed of the oil pumps. 



The outlet from the tank to the machinery should be well above the bottom 

 and there should be other means of drawing oil from the bottom of this tank to a 

 filter or settling tank. The character of the oil in the bottom of this gravity tank 



