Hydraulic Cylinder Basics: Anatomy, Sizing, and How They Work
Anatomy of a Hydraulic Cylinder
Cylinders come in two basic categories, single acting, and double acting. A single acting cylinder has one port for fluid to enter and exit. This port can be located on either end depending on if you want to move a load on either the extend or retract positions. To get the cylinder to move in the other direction, the cylinder either relies on the weight of the load and/or a spring to help the cylinder return to its resting position.
Double Acting Cylinders have at least two ports. This allows fluid to flow in one end to extend the cylinder and the other end to retract the cylinder. This is helpful in any applications where you need to be able to push and pull the load.
How is a cylinder measured?
A typical cylinder has measurements notated like A x B x C. Where “A” is the diameter of the large end of the cylinder, “B” is the length of the cylinder stroke, and “C” is the diameter of the cylinder rod. For example, you may have a cylinder with dimensions 4” x 12” x 1”. The bore of the cylinder would be 4 inch in diameter, the stroke would be 12 inches, and the cylinder rod would be 1 inch in diameter.
How is a cylinder measured?
A cylinder works based on the relationship between Force, Pressure and Area, where Force = Pressure x Area.
You may find this relationship represented in a graphical form like this:
For example, if you have a cylinder that is 4” in diameter and a system pressure of 3000 psi, you can find how much force the cylinder can move. The first step would be to use the diameter to find the ‘Area’ of the cylinder. A 4” diameter cylinder would have an area of 12.566 in.². Using our formula, Force = 3000 psi x 12.566 in.², the force this cylinder would be capable of moving would be 37,698 lbs. at 3000 psi. By adjusting the system pressure and or the area of the cylinder used, one can change the capable force of that cylinder. This is not, however, the same force that is available when the cylinder is retracting. To figure that out, you must subtract the area of the rod from the overall cylinder area. For example, if you have a 1” diameter rod, the area of that rod would be .7854 in.². I would then take the overall area of 12.566 and subtract the rod area from that, 12.566” - .7854” = 11.781 in.². We call this the Effective Rod End Area or EREA. If we replace the cylinder area with the EREA, the formula looks like this, Force = 3000 psi x 11.781 in.². The force available on retract would be 35,343 lbs.
Let a FORCE America salesperson help you with your cylinder needs
A FORCE America salesperson will be able to help you size a cylinder for your application needs. Other items that need to be taken into consideration are how the cylinder is going to be mounted, is the going to lift the load at an angle, and should it be a single or double acting cylinder. Our knowledgeable sales team will be able to help outfit any application.