How Hydraulic Cylinders Work?

Hydraulic cylinders are remarkably simple, nothing more than a steel tube & rod and other bits holding it all together, but so incredibly powerful. They are truly the workhorse of our world, provide the muscle that moves & forms the earth & structures around us. But do you know how hydraulic cylinders work? How does something so simple & relatively small do such an amazing amount of work?

The PISTON is the part inside the cylinder that the fluid pushes against. The diameter of the cylinder piston is called the BORE. The larger bore cylinders have more force exerted upon them, therefore a higher lifting capacity. The hydraulic fluid is contained by the piston seal. That’s why a cylinder with a defective piston seal will not lift as much as it should. Even though the cylinder may not be leaking on the outside, a damaged piston seal will allow oil to bypass the piston, so the pressure will not reach the required level to do the lifting that is expected.

The ROD (or shaft) of the cylinder is the part that travels through the GLAND (or head) of the cylinder and attaches the piston to the end fitting (usually a clevis, cross-tube or tang). The diameter & hardness of the rod are important because the further out it is extended, the more “side-load” is exerted on it, increasing the risk of bending. That’s why higher pressure cylinders have stronger rods, so that if they are lifting a heavier load they are less likely to bend. This is commonly know in the industry as COLUMN LOAD. Welded hydraulic cylinders typically have an “induction-hardened” rod, which is harder to bend.

The STROKE is the difference fully retracted length and the fully extended length of the rod. This is the total travel of the cylinder.

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