464 SEC. 12. APPLIED MECHANICS. 



137 7a. Photographs (2) of Frank Pearn's Double and 

 Quadruple acting Steam Bam Pumps for feeding steam 

 boilers with water. Frank Pearn & Co., Manchester. 



South Kensington Museum. 



1993a. Davey's Compound Differential Expansive 

 Pumping Engine. Hathom $ Co. 



The main slide valve spindle is attached to the centre of a differential 

 lever, one end of which derives its motion from the engine, and reciprocates 

 with the steam piston, whilst the other end is actuated by means of a sub- 

 sidiary piston, caused to reciprocate in equal times by means of a double 

 acting cataract governor. The movement of the cataract end of the lever is 

 constant, and independent of the motion of the main piston of the engine, 

 and has necessarily a lead in advance of that of the opposite end at the com- 

 mencement of each stroke. With a constant load on the engine the lead will 

 be constant and the cut off constant, but the slightest variation in the load 

 causes a corresponding instant variation in the lead, and as a consequence the 

 cut off takes place earlier or later, as the load is decreased or increased. The 

 engine thus automatically varies the expansion to suit the varying conditions 

 of resistance. 



1993b. Davey's Hydraulic Pumping Engine. Worked 

 by means of a natural or an artificial head of water. 



Henry Davey. 



In this engine there are no pistons, but the power is applied and the work 

 done entirely with plungers. The power plungers are stationery, and are 

 made to serve as pipes to convey the water from the valve box (to which 

 they are fixed) to the inside of the pump plungers ; these latter forming the 

 power cylinders and being connected to each other by side rods passing out- 

 side the valve box. In this way the forcing stroke of one pump plunger 

 causes the suction stroke of the other, and vice versa. In " dip " workings 

 in collieries these engines are used to raise water to the main pumping 

 engines, the motive water in this case being supplied from the rising main of 

 the main engine. In hilty mining districts, too, water drawn from a high 

 level is conducted by pipes into the mines and then used to raise water to 

 the surface, thus avoiding the necessity for steam power. The valves of the 

 engine are worked without any metallic connexions by means of water pres- 

 sure through a small valve actuated by Davey's differential gear. 



2062. Model of Force Pump. Prof. W. F. Barrett. 



2063. Model of Ordinary Water Pump. 



Prof. W. F. Barrett. 



1989. Model of Sand Pump. 



The Council of King' s College, London. 



1989a. Air Water Pump, by Jagn. 



R. Nippe, St. Petersburg. 



2064. Model (to scale) of Centrifugal Pump. 



Lawrence and Porter. 



This pump has been patented by Messrs. Lawrence and Porter. The chief 

 feature of the patent is the arrangement of making one side of the casing 

 removable. The advantages of this system are as follows : By taking off the 



