The diagram of Fig. 142 illustrates the working principle of the double-acting hydraulic ram mentioned above; where the water from a muddy stream is used to drive the ram and that from a separate source, as a spring is delivered.

Fig. 142. - Sectional view of a double-acting hydraulic ram.

The construction of the double-acting ram is similar to the single-acting ram, but a separate pipe S discharges spring water directly below the valve which acts just as though it had entered at the drive pipe. The ram in this case is receiving water from the drive pipe D, which operates the valve and furnishes power for elevating the spring water. The spring water enters the ram through the pipe S, to keep the space T filled, directly under the valve. The water which enters the air chamber is, therefore, only that from the spring.

A standpipe is arranged as shown in the figure, with a check valve to prevent the water in the ram from being forced back into the spring water pipe after entering the ram.