the mouth of B A is sufficient to prevent the formation of a vacuum.
THE BUCKET PUMP.
We may now pass to the commonest form of pump used in houses, stables, gardens, etc. (Fig. 174). The piston has a large hole through it, over the top of which a valve is hinged. At the bottom of the barrel is a second valve, also opening upwards, seated on the top of the supply pipe. In sketch ( a ) the first upstroke is in progress. A vacuum forms under the piston, or plunger, and water rises up the barrel to