How Do Hydraulic Cylinders Work

Hydraulic cylinders power machinery to tunnel through the earth and move heavy loads. The mechanism for powering these heavy-duty machines are simple in their basic design. Beyond the basics, there are a variety of sizes, power, and design features that make them versatile in their applications.

The Idea is Quite Simple

The cylinder itself has a few main parts that create a linear motion. There is the barrel, piston, rod, gland, and butt. The barrel is a metal casing that is able to withstand pressure. The body of the casing is cylindrical with varying length, and usually made of steel, aluminum, cast iron, or bronze. Other materials may be used as well. The rod is strong and often made of steel. It’s affixed to the piston, which together move up and down along what’s called the fluid path. This is important as the rod must also be stable in the presence of the fluid long term. For example corrosion from the fluid would compromise the life and effectiveness of the hydraulic cylinder. The gland is the front part of the cylinder and the butt is the base.

The Liquid is a Key Component

Pressurized liquid is responsible for the motion of the piston and rod. The liquid often uses mineral oil or water based. Different hydraulic fluids will exhibit different properties, and one such property is being non-compressible. Despite not compressing under force, the hydraulic liquid can exert immense pressure. Other properties include:

  • thermal capacity
  • conductivity
  • low volatility
  • minimal foaming
  • viscosity
  • inflammability
  • low toxicity
  • radiation resistant
  • biodegradable

The crucial part of the the design is how area and pressure work. One pound of pressure on a surface area of one inch squared will yield a force of one pound. Double the area, and the force also doubles. Force responds to area quickly, which makes the hydraulic cylinder incredibly powerful for multiplying pressure.

Because the cylinder is composed of different parts and works under immense pressure, it’s important for the different pieces to form perfectly. The seals around the rod and piston are crucial for containing the pressure. The better the seal, the more effective the cylinder.

How Do Hydraulic Cylinders Work

The rod will travel great distances over the life of the hydraulic cylinder. The stroke is defined as the length between the piston when fully extended and fully retracted. As the piston goes up and down, it will travel twice the distance of the stroke. The larger the area of the piston, the greater multiplying force. Technically, the inside of the diameter of the tubing is called the bore, which is a good, rough estimate of the piston.

Compared to the volume of a similarly sized electric motor, the hydraulic cylinder can have several times the power. Typically, there are other constraints that limit the choices for choice in cylinder. Stroke length can be as small as an inch to several feet. Bore diameter usually only extends to 24 inches.

Configuration and Mounts

There are three main designs: tie-rod, welded, and ram-style. Tie-rods uses threaded rods while welded cylinders with the barrel welded to the end caps. Ram cylinders don’t operate in the usual push-pull. Instead, only the push motion is powered. Single-acting pistons return to the starting position through gravity working on the weight of the rod, piston, and fluid, whereas double-acting relies on the expansion of the fluid.

There are four popular mounting methods: flange, side-mounted, centerline, and pivot. Mounts are used to support loads, making the setup more stable and durable. The most popular choice is the flange mount, which is very strong but must operate under very strict conditions. Misalignment must fall within narrow tolerances. Likewise, side-mounted cylinders also need alignment, although not necessarily to the same degree. This type of cylinder usually rotates, which introduces wear into the system.

Centerline lug mounts don’t require such precision. A useful feature is its ability to absorb forces. The force is distributed along dowel pins under high pressure or shocks. A pivot mount equipped with a clevis, trunnion, or ball bearings allow rotation to occur. Attachments should also permit pivoting for spinning to work.


With a well designed system, hydraulic systems are relatively simple and therefore less prone to complications. Regular maintenance include filtering or changing the hydraulic fluid when it’s no longer functioning well enough. Replacement of seals is also important as over time, wear-and-tear will gradually degrade the quality of the seal. Once compromised, leaking may occur, corrosion may speed up, or contaminants can spread to the hydraulic liquid.

Author Bio:

Michael C Nelson is a small engine mechanic who loves exploring all aspects of technology. He love to share his knowledge with others. He is a major gadget nerd an d is a sucker for whatever’s the latest and greatest. Contact him at Twitter