CONSTRUCTION OF PUMP 297 



is lowered. C C are the two barrels, K K the two 

 pistons, v v the suction- valves, V V the pressure-valves. 

 The two tubes r r join so as to form one suction-tube, 

 R ; the lower end of it is closed by a sieve to prevent the 

 entrance of foreign bodies, as sand, etc., and is dipped 

 below the surface of the water in a reservoir. The 

 two pressure-valves open into the air-vessel TF, which 

 has in the side an aperture #, into which a flexible hose 

 may be screwed which ends in a jet-pipe. The solid 

 pistons K K being alternately forced down upon the 

 water which has been drawn into the barrels upon the 

 principles already explained, the water is forced into 

 the air-vessel Tf, and if the lever is worked with 

 sufficient rapidity, more water will be conveyed into 

 the air-vessel than can be discharged in the same time 

 through the jet-pipe; the air in the vessel W will thus 

 be somewhat compressed, and acts by its elastic force 

 as the air in the flask, fig. 169, that is, a continuous jet 

 is produced which is not interrupted even when the 

 action of the pumps ceases for a short time, as in fact it 

 does for an instant every time the motion of the pistons 

 is reversed. 



Fig. 198 A is an easily constructed model of a suction -pnmp. The 

 i cylinder is made of glass tube with strong sides about 15 cm long, 

 and so wide that a piece of india-rubber just fits into it ; about I4^ m 

 is the best width for the bore of the glass tube. A small wooden 

 'rod, s t cut neatly round and straight, forms the piston-rod ; its 

 diameter at the lower end should be 3 nun less than the bore of 

 the india-rubber tube ; and the upper part may be somewhat 

 thinner. The handle G is cut out of a thicker piece of wood ; it has a 

 bole bored in the middle, is glued to the rod, and for greater safety 

 i wire pin is driven across through the rod and the handle. The 

 listen is made by tying about 15 or 18 mm of the india-rubber tube 

 ound the end of the rod, as shown at B in the figure; the 

 'ubber tube then acts like the leather collar in a common pump ; 



