Hydraulic cylinders convert the energy produced from a hydraulic pump into a linear mechanical output so that they can perform useful work.

Hydraulic cylinders are sometimes also referred to as hydraulic rams, hydraulic jacks, linear hydraulic actuators, and hydraulic actuators. These terms are all synonymous although the terms "hydraulic ram" and "hydraulic jack" are usually applied to short stroke, single acting cylinders with large diameter piston rods. Hydraulic cylinders are the muscles of machinery.

Above: A cut away diagram showing the internal components of a welded body hydraulic cylinder.

Hydraulic cylinders are so named because they consist of a piston that moves through a smooth round cylinder or tube. This cylindrical tube must be sealed at both ends with end plates. The end plates are also called end caps or cylinder heads. The piston is firmly connected to a shaft called a piston rod that exits the cylinder through a hole in one end cap. This is called the rod end. The opposite end of the cylinder is called the cap end or the blind end (because it does not have an eye for the rod to stick out).

Above: A Cut Away Diagram of a Typical Hydraulic Cylinder Labelled with the Correct Component Names.

The cylinder end caps also usually contain the ports where hydraulic fluid is admitted into the cylinder.

The piston rod is the working end of the cylinder and is usually fastened to a load that must be moved. The opposite end of the cylinder body is called the cap end or blind end. It is usually attached to a surface which the actuator pushes against although a large variety of mountings are available that can be mounted at various positions over the body of the actuator.

The cylinder barrel or tube is usually made from high strength seamless steel tubing that has been honed or skive roller burnished to a fine finish on the inside diameter. This will provide a smooth surface for the hydraulic piston to slide through. The tube must be of sufficient thickness to contain the hydraulic pressure that will be used. In a welded body hydraulic cylinder, the barrel must also provide the mechanical strength and rigidity to support the loads that the body of the actuator will see. This is especially true when a mid trunnion mount is attached to the center of the cylinder barrel.

Above: Large bore, high pressure, hydraulic cylinder barrels.

The amount of distance that a hydraulic cylinder is able to push the piston rod is called the cylinder stroke or travel.

The amount of force that a cylinder is able to produce is directly related to the area of the piston to which the hydraulic fluid is exposed and the pressure of the hydraulic fluid. The larger the piston area, the more force is produced. The higher the pressure of the hydraulic fluid, the more force is produced. This amount of force is also called the cylinder capacity. It is measured in Pounds of force (lbsf), Tons of force, Newtons of force (N), or Kilograms (Kgf) of force. This force capacity is determined using the basic mathematical formula F=PA, where F= Force, P= Pressure, and A= Area. this equation is easily manipulated to determine the correct size of a cylinder for a required force, or the hydraulic system pressure required to produce a force for a given cylinder.

It should be kept in mind that the effective piston area on the rod end of a hydraulic cylinder is reduced by the area of the piston rod. The piston rod area must be subtracted from the total piston area to find the effective area of the piston being used during the retraction stroke. The force of a cylinder produced while retracting (or pulling) will always be less than the force produced when the cylinder is extending. The larger the diameter of the piston rod, the greater effect it will have in reducing the force of the cylinder in retracting.

A rod cylinder with a large diameter piston rod will retract with much less force than on extension due to the area of the rod subtracting from the total area of the piston as on these oil field cylinders shown above.

Hydraulic cylinders are specified by bore size, stroke, mounting style, rod diameter, and pressure rating. Other details include seal material, temperature rating, materials of construction, cushioning, and more.

Hydraulic rod cylinders are often shown in machine diagrams by the following standardized ISO symbol:

Above: The Internationallt Recognized ISO Symbol for a Hydraulic Cylinder


Hydraulic cylinders as per OE Designs and specifications
Bore Size : - 45 mm to 600 mm
Rod Size : - 20 mm to 400 mm diameter
Stroke : - Up to 4000 mm
Pressure : - Up to 700 Bar
Mounting : - All standard mountings like Flange, Clevis, Foot and Trunnion type.

Hydralic Cylinder
Pneumatic Cylinders
Reconditioning of Hydraulic Cylinders
Suspension Cylinder
Hydraulic Jack
Chrome Plated Piston Rods
Honned Tubes
Hydraulic Fittings
Brass Male/Female Inserts
Seal kit for Hydraulic Cylinder
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