CONVICT LABOR FOR ROAD WORK. 83 



pump method. Those who favor this method claim as an additional 

 advantage the fact that the water is not stored in a closed tank or in 

 contact with stale air. On the other hand, the equipment necessary 

 is more expensive than that required for the operation of the hydro- 

 pneumatic tank method, and the mechanism of the pneumatic pump 

 is somewhat dehcate and demands careful attention to keep it in good 

 running order. In particular, the pump must be protected from the 

 action of sand or grit in the water. ♦ 



There are two general types of pumps, namely, suction-lift pumps 

 and force pumps. The former depend for their action on the creation 

 of a partial vacumn in the piunp cyhnder, which permits the water 

 in the pump to rise above thq water in the well. The maximum 

 practical suction Hft is about 20 feet, though it varies somewhat 

 with the elevation above sea level, the greater the elevation the 

 smaller the suction hft. This means that the pump cylinder which 

 raises the water by suction in Uft pumps should never be more than 

 20 feet above the water level in the well or other source. In force 

 pumps the water is raised mechanically and the height to which the 

 water can be raised is not limited as in the case of the suction pimaps. 

 Pumps of this type are necessary for use in connection with elevated- 

 tank or hydropneumatic systems, and, unless a special air pump or 

 compressor be used, it is necessary that a combination air-and-water 

 force pump be employed for the hydropneumatic systems, especially 

 in pumping from deep weUs. 



Frequently the two types of pumps are combined, the water being 

 raised partly by suction and partly by force. This is accomplished 

 either by the use of two cylinders, one for each of the operations, or 

 by a combined suction and force cylinder. 



Pumps are manufactured suitable for operation with any kind of 

 power — hand, gasoUne, steam, or electric. The most suitable form of 

 power for the use of convict camps is that of the gasohne engine. 

 For the purposes of camps of ordinary size from 2^ to 3 horsepower 

 is all that is required, and a gasoline engine of such rating will not 

 only pump all the water necessary but will furnish sufficient power 

 to run a clothes-washing machine or other small machinery which may 

 be useful around the camp. The horsepower necessary for pumping 

 purposes in any case may be estimated by the following method: 



Divide the number of gallons which it is desired to pump per 

 minute by 7.48 (the number of gallons in a cubic foot), to determine 

 the number of cubic feet of water to be pumped per minute. Multi- 

 ply the number of cubic feet by 62.5 (the weight in pounds of a cubic 

 foot of water) to get the weight of the water to l)e pumped per min- 

 ute. Multiply this weight by the total lift in feet. The total lift 

 will be equal to the vertical distance from the surface of the water 



