How to Choose the Right Hydraulic Cylinder

Mass
The first and most critical step is to determine the amount of mass you wish to move. Once your mass is known, you must then consider the effect that the mass will have on the force required to move it. For example, a 1-ton load being pushed straight up will require just over 1 ton of force, however, a 1-ton load being pushed across the ground will require only enough force to overcome friction and acceleration. Regardless, the force of the cylinder should always be high enough to allow for margin of error.

Geometry
Once you know the nature of the mass being moved you then need to consider the geometry involved in moving it. For a machine such as a hydraulic press, which moves typically up and down, the geometry is simple and requires no further consideration. However, when the centre of the load being moved is not centered on the point of lift force and at perpendicular angles to that point of lift force, the force required by the cylinder changes. If you have a crane, for example, the cylinder pushes on the boom often very far from the load. In most cases the load distance (distance from load to fulcrum) can be up to ten times the lift force (distance from lift force to fulcrum), and sometimes more. So the closer your point of lift is to the fulcrum the more force is required by the cylinder to lift the load.

Bore size
Once you arrive at the force required by your cylinder, the next step is to calculate the bore size required of the cylinder. The force produced by the cylinder is simply the product of the system pressure multiplied by the area of the internal piston surface upon which that pressure acts. This formula is used to calculate the bore size needed to achieve that force.

Rod size
Once a minimum cylinder bore size is determined the next step to the selection of a hydraulic cylinder is to select an appropriate rod size. Most standard off the shelf cylinders usually come with one or two rod options. Selecting the required rod size requires careful consideration of the stroke length required which affects the rod buckling strength.

Cushions
Once the bore, rod and stroke sizes have been determined another consideration is to whether internal cushions at the end of the cylinder stroke are required. The use of cushions is recommended for deceleration of high speed rods to reduce the energy of the impact of the piston assembly against the cylinder end cap. Cushions are optional and can be supplied at either one or both ends of the cylinder as desired. The use of cushions does not affect cylinder envelope or mounting dimensions.