COMMON THINGS PUMPS. 



Of the valves which are opened by a motion perpendicular tx> 

 their seat, the most simple is a flat metallic plate, made larger 

 than the orifice which it is intended to stop, and ground so as to 

 rest in water-tight contact with the surface surrounding the 

 aperture. Such a valve is usually guided in its perpendicular 

 motion by a spindle passing through its centre, and sliding in holes 

 made in cross bars extending above and below the seat of the 

 valve. 



11. The conical valves, usually called spindle-valves (fig. 

 10), are the most common of this class. The best angle to 



Fig. 10. k e given to the conical seat is found in 



practice to be 45. With a less inclination 

 the valve has a tendency to be fastened in 

 its seat, and a greater inclination would, 

 cause the top of the valve to occupy unne- 

 cessary space in the valve-box. The area, or transverse sectioc 

 of the valve-box, should be rather more than double the magni- 

 tude of the upper surface of the valve, and the play of the valve 

 should be such as to allow it to rise from its seat to a height not 

 less than one-fourth of the diameter of its upper surface. 



12. The valves coming under this class are sometimes formed as 



spheres or hemispheres (fig. 11) resting in a 

 conical seat, and in such cases they are 

 generally closed by their own weight, and 

 opened by the pressure of the fluid which passes 

 through them. 



13. The several expedients already described 

 'are, however, greatly surpassed in convenience 

 by the form of pump almost universally used 

 in domestic and general economy, and known as 

 the sucking or suction pump. 



A section of this useful apparatus is shown in fig. 12, p. 169. 

 It consists of a pipe or barrel, s o, which descends into the 

 well, and the length of which must not exceed 32 feet. Attached 

 to the top of this pipe, which is called the suction-pipe, is a large 

 syringe, acting precisely on the principle of a common exhausting 

 syringe. 



At the commencement of the operation, the pipe s E is filled with 

 air to the level of the water in the well. The operation of the 

 syringe draws the chief part of the air out of this pipe s E. When 

 the water within the pipe is partially relieved from the atmospheric 

 pressure, the weight of the atmosphere, acting upon the external 

 surface of the water in the well, forces it up in the pipe s E ; and 

 according as the air is withdrawn by the syringe, the water con- 

 tinues to rise, until it passes through the valve x. This valve 

 184 



