The simple design of Hydraulic Cylinders

Hydraulics is the liquid version of pneumatics. Fluid mechanics provides the foundation for hydraulics and this focuses on the applied engineering using the properties of fluids. The main use for hydraulics is the generation, control, and transmission of power through the use of pressurized liquids. Hydraulic cylinders are an important part of mechanical equipment, tools and vehicles.

A hydraulic cylinder is a mechanical mechanism that is used to give a unidirectional force through a unidirectional stroke. It is used in construction equipment, manufacturing machinery  and civil engineering.

A hydraulic cylinder has many components. Below we’ve outlined some of the main parts:

Cylinder barrel

The main function of a cylinder barrel is to hold pressure. It is mostly made from a seamless tube. The piston reciprocates in the cylinder.

Cylinder base or cap

The main function of the cap is to enclose the pressure chamber at one end. The cap is adjoined to the body by welding, threading, bolts, or tie rod. Caps also perform as cylinder mounting components.

Cylinder head

Its function is to enclose the pressure chamber from the open end. The head contains an integrated rod sealing arrangement.


The piston is to separate the pressure zones inside the barrel. The piston contains grooves to fit elastomeric or metal seals and bearing elements. These seals can be single or double acting.

Piston rod

The piston rod is a hard chrome-plated piece of cold-rolled steel. It attaches to the piston and extends from the cylinder through the rod-end head.

Seal gland

The cylinder head is fitted with seals to prevent the pressurized oil from leaking .This area is called the seal gland.


The seals are designed according to the cylinder working pressure, speed, operating temperature, working medium and application. Piston seals are dynamic seals and could sometimes be single acting or double acting.

What does single-acting and double-acting mean?

  • Single acting cylinders – they are economical and the simplest design. Hydraulic fluid enters through a port at one end of the cylinder. It extends the rod by means of area difference. An external force returns the piston rod.
  • Double acting cylinders – They have a port at each end of the piston. It is supplied with hydraulic fluid for both the retraction and extension.

Can hydraulic cylinders be repaired?

Yes, they can. You can dissemble and rebuild an entire mechanism. Inspection of leakage and scrutinizing cylinder parts (especially the seals) is helpful in diagnosing the problem and deciding how to repair the cylinder.

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