This differs from the one just described chiefly in that it is single-acting, while the other is double-acting.
By single-acting is meant that the air cylinders compress their respective volumes of air once every revolution.
The double-acting engine, unlike the single-acting pumping engine, required a piston rod that would push as well as pull.
The piston will, therefore, be pressed downwards by the action of the steam above it, as in the single-acting engine.
A chain from the piston-rod to the arch head, as described in the single-acting engine, would fail to transmit this force.
The piston P is accurately fitted in the steam cylinder C by packing, as already described in the single-acting engine.
As single-acting pumps give an intermittent discharge three are generally used on cranks at 120.
The engine, it will be seen, is single-acting, and no compression of the explosive charge is employed.
Each sliding platform was actuated by two single-acting rams, 3½ in.
The surface-condenser is cleared by a single-acting air-pump, inside the frame, at T.
