Figure 31 a - A lift pump; b - A force pump

 

In order to obtain a steady stream of water from the pump, an air cushion С is provided. On the downward stroke of the piston, the air in this chamber is compressed by the water flowing into it from the delivery pipe. While the piston is making its upward stroke, the compressed air in this chamber expands and forces water through the delivery pipe. That results in this way a more or less steady stream of water through the delivery pipe. The compressed air in this chamber tends to prevent the jars and shocks that would accompany the starting and stopping of the water if it flowed only on the downward stroke of the piston.

Measuring Pumps. — Pumps are often used in measuring the vol­umes of liquids, especially in the sale of gasoline. The ordinary piston pump can be used for this purpose, if means are provided for defining the length of the stroke and ensuring that each stroke of the piston will discharge the same volume of liquid. This requires that the valves be tight and the piston close fitting so as to prevent leakage or slippage of the liquid past the valves or the piston. Such pumps may discharge either on the upstroke or they may discharge on both the upward and downward strokes. In the former case, they are said to be single-acting pumps and in the latter case they are known as double-acting pumps [2, С. 82 - 83].

 

2.10.4 Look through texts 2.10 and find the English equivalents for the following Russian phrases and word-combinations:

1.500 фунтов на квадратный дюйм; высота жидкости, умноженная на ее плотность; как показывает общая практика (опыт); посредством малого насоса; площадь в сто раз больше площади малого поршня; одна сотая расстояния; для того, чтобы увеличить давление; целиком или полностью погруженное тело; для того, чтобы определить плотность тела; заставить его (тело) опуститься ниже; вплоть до; для того, чтобы достигнуть постоянного потока; таким образом; в первом случае; в последнем случае.