Single-acting hydraulic cylinders function unidirectional, with hydraulic force propelling the rod forward while the return stroke relies on gravity, a mechanical means, or external forces. Unlike the double-acting counterparts, single-acting cylinders may lack a piston, relying solely on the pressure applied to the piston rod's cross-section to extend. An illustration of their application is evident in hydraulic trucks or trailers, where these cylinders facilitate lifting actions and gravity down without any power .
Double-acting hydraulic cylinders are designed for dual-direction operation, utilizing hydraulic pressure for both extension and retraction. The presence of a piston within the cylinder enables separate pressurization of each side, resulting in seamless back-and-forth movement. Their capability to generate substantial force in both directions makes them integral components in machinery like excavators, where the boom must be precisely maneuvered with equal force to move in and out.
Reference: https://en.wikipedia.org/wiki/Single-_and_double-acting_cylinders
