VALVtt 



\\ I V \I. 



Profess^' ule* valves, accor<< 'hair con- 



three classes an follows :-(!) flap valves, which 

 bend or turn uj-.n a hin' ; * perpen- 



dicularly to the teat - ,, * Inch move parallel 



!>6 Mat 



Examples of flap valvoa are shown in figs. 65 and 66 ; two 

 form* ilvea are shown in figs, 67 and 68, and in figs. 



69 and 70 are shown two forms of glide valve. The slid* 

 shown in fig. 69 moves in A t-tnii^ht In,.-, while that shown in 

 fig. 70 (called a cock) moves 



/H./I.I /</,'" / IWev*. In india-rubl* r \alvea there is a 

 1 covered by a piece of imlia- rubber, which may be rect- 

 angular. > >ut in generally circular, and which in held down 

 along one edge if rectangular, or at the centre if circular. 

 Water or -th, r ilui.l can pass freely upwards through the 

 t attempt* to return the elasticity of the 

 india-rul'l* r. ;ul t he pressure of the water upon it, cause it to lie 

 close on the grating, and thus prevent the the water. 



The fadia-ivbbsr is prevented from rising too high by a per- 

 forated guard. In fig. 65 is shown an example of an 

 r disc vah .tating, B the india-rubber 



guard secured to the grating or seat by the stud D and nut 

 i in position by bolt* and nut* P. The 

 ug and guard are generally of brass. 

 India rubier (list- \ iilvea are also shown <>M tl..- air-pump 



EXKBCISK 68 rubber Disc Valve. Fig. 65 shows a 



vertical eciion and a plan of an india-rubber disc valve. In ilu> 

 plan one-half of the guard anil india-rubber are supposed to be re- 

 moved, so an to show the grating or seat Draw these views, and 

 also an elevation. A detail drawing of the central tnd is shown in 

 fig. 10, page 18. In fig. 65 the elevation of the guard is drawn at 

 it is usually drawn in practice, but if the student hat a sufficient 

 knowledge of descriptive geometry he should draw the elevation 

 completely showing the perforations. Scale inches to a foot. 



