The basic difference of single acting hydraulic cylinder and double acting hydraulic cylinder lies in the mechanism of operation of these two types of cylinders. In a single-acting cylinder hydraulic fluid acts only at one side of piston of cylinder. Pressure generated by the pump is transmitted through the fluid to extend the piton. In single acting hydraulic cylinder, the spring retracts to its original position by the force generated either by gravity or by the weight load. But in case of a double acting hydraulic cylinder, hydraulic fluid acts on both sides of piston. These cylinders have ports at both ends for retraction and extraction of piston and force is produced at both ends. In double acting hydraulic cylinders no external force is required for movement of piston to both sides.
The difference between a single acting hydraulic cylinder and double acting hydraulic cylinder that you can tell simply by looking at the cylinders is the number of ports these cylinders have. A single acting hydraulic cylinder typically has one port. This port is connected with the pump through the hydraulic hose fittings and the pressure is applied through this hose to extend the piston and the piston is then retracted to its original position by the weight. While in case of double acting hydraulic cylinders there are two ports attached to the cylinders. One port that is referred as the advance port is used to attach the hydraulic hose and extend the piston and the other port is used to retract the piston.
A single acting hydraulic cylinder is simple machine that is easy to assemble, install and maintain. On the other hand, the double acting hydraulic cylinders are complex machines that require more maintenance and comparatively difficult to install.
Functioning and maintenance of Double acting hydraulic cylinders are more complex than that of single acting hydraulic cylinders but they are good for completing repetitive jobs. Double acting hydraulic cylinders offer better precision in terms of application. So, if the job demands high precision and repetitive action double acting hydraulic cylinders are always better option to choose. Both the single acting and double acting hydraulic cylinders have their own advantages and disadvantages. It depends on the requirement of the job on the basis of which you need to select the type of cylinder.