500 APPLIED MECHANICS 
pressure, the bucket is pulled upwards, the valve in it being kept shut by 
its own weight and the excess pressure of the air above it. As the spac 
between the bucket and the suction valve increases, Hiaae 
the air in that space expands and its pressure falls. x 7 
This enables the pressure of the air in the suction ie 
pipe to lift the suction valve, and a portion of that t 
air then flows into the barrel below the bucket. 1 
The pressure of the air in the suction pipe there- : 
fore falls below the pressure of the atmosphere, 1 
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and in consequence water is forced into the suction 
pipe from below by the pressure of the atmosphere 
outside until the water stands at such a height that 
the pressure at E due to that column of water, and 
the pressure of the air above it, is equal to the 
pressure of the atmosphere. During the down- hk 
ward stroke of the bucket the air beneath it is c ' 
compressed, the suction valve having closed, and ; 
when the compression is sufficient, the bucket valve B i 
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opens and a portion of the air beneath the bucket ret 
passes through it into the space above. In the D 
next upward stroke the air beneath the bucket is 
still further rarefied, and the water is forced by 1 
the pressure of the atmosphere to a greater height EES a 
in the suction pipe. This goes on until the water i i 
gets into the barrel. The bucket in descending Fra. 800. 
then enters the water, part of which passes through 
the bucket to the space above. The whole space below the bucket within 
the barrel and suction pipe is now full of water, and subsequent up strokes — 
of the bucket lift the water higher and higher, until it reaches the top « ‘” 
the delivery pipe. After this, during each up stroke, a volume of water 
equal to the volume swept through by the bucket is discharged through — 
the delivery pipe. 4 
Since the water beneath the bucket is held up by the pressure of the — 
atmosphere it is evident that the bucket in its highest position must not — 
be at a greater height above E than the height of the water barometer. — 
For a pressure of 14°7 lbs. per square inch the height of the water 
barometer is 34 feet. The height of the bucket above the level of the 
water at E is called the suction head. In practice the suction head is 
generally not more than about 26 feet. 
It may be observed that in the pump just described the dclivell - 
valve is not absolutely necessary, but during the down stroke of the © 
bucket it acts as a check on the suction roe in holding up the column 
of water. ‘ 
433. Force required to Work a Bucket Pump. —Once the barrel atid 
pipes of the pump are fully charged with water it is evident that, neglect- ~ 
ing the volume of the pump-rod, the volume of water delivered during 
each up stroke of the bucket is equal to the volume swept through by the 
bucket in one stroke. Let a=area of bucket in square feet; /= length 
of stroke in feet; h=total height through which the water is raised, in 
feet ; P = force (in Ibs.) required to lift the bucket, neglecting friction and ; 
the weight of the bucket and bucket-rod. 
