Hydraulic cylinder design explained: from the piston rod to the sealing ring

Hydraulic cylinders are the powerhouses of modern machines. In excavator arms, presses or cranes, they convert oil pressure into lifting power weighing several tonnes.

Behind the seemingly simple design lies a precise interaction between the cylinder tube, piston, piston rod and often extensive sealing and guide systems.

The service life of a hydraulic cylinder is largely determined during the design phase. Factors such as the choice of materials, piston rod coatings and the design of connecting elements have a significant impact on service life, maintenance requirements and, ultimately, the costs of maintenance and repairs.

Functionality and main components of hydraulic cylinders

Hydraulic cylinders convert oil pressure into a linear force by moving the piston back and forth in a closed working chamber. The perfect interaction of all components determines efficiency, performance and service life.

The main components at a glance:

• 1.

  Cylinder tube – pressure-resistant housing for guiding the piston
• 2.

  Piston – separates working chambers, transfers pressure forces to the piston rod
• 3.

  Piston rod – transmits axial forces from the cylinder to the outside
• 4.

  Cylinder base – front end closure
• 5.

  Cylinder head – guides the piston rod, accommodates guide and sealing elements
• 6.

  Seals and wipers – ensure system tightness and protection against contamination

The piston moves inside the cylinder body. The direction of movement depends on the fluid supply: if the fluid is fed into the piston chamber, the piston extends; if the fluid is fed into the rod chamber, the piston retracts. At the same time, the fluid is discharged from the other chamber.

A hydraulic unit builds up pressure in the cylinder chamber, which acts on the respective piston surface. This pressure generates a force that acts on the piston rod. However, pressure is only built up if there is a corresponding counterforce.

Primary and secondary seals keep the oil in the cylinder, while scraper rings trap dirt particles before they reach the seals.

Comparison of cylinder types

Hydraulic cylinders can be divided into three tried-and-tested basic designs. They differ in terms of force direction, installation space and control behaviour. The choice of the appropriate design not only influences functionality, but also maintenance requirements, dynamics and energy efficiency of the entire system.

Single-acting / plunger cylinders

These cylinders generate a force in only one direction of movement. The return is passive – for example, via dead weight, spring force or external loads. They are mainly used as press cylinders, clamping devices or lifting systems. Due to their simple design, they are particularly low-maintenance.

Telescopic cylinders

If installation space is limited, multi-stage telescopic cylinders offer a compact solution with high lifting capacity. Large strokes can be achieved in the smallest of spaces thanks to interlocking piston stages. Telescopic cylinders are found in cranes, tipping vehicles and work platforms, among other things. The design effort is higher, but the system offers advantages in terms of weight, space requirements and flexibility.

Double-acting hydraulic cylinders

As an industrial standard, double-acting hydraulic cylinders enable precise control and rapid reversal of movement. Both sides of the piston can be actively pressurised, allowing for exact positioning and controlled acceleration and braking processes. Applications range from machine tools and presses to robotics and conveyor technology to systems in packaging or plastics processing.

Connection techniques between cylinder tube and bottom

The interface between the tube and the bottom is a key factor in terms of both design and economy – in practice, it is usually implemented as a welded construction, bolted bottom or tie rod connection.

Welded connections

Welded connections are widely used because they are easy to manufacture and enable a very compact design. However, the weld seam is the weakest point of the construction. That is why we at ACONA have developed the deep-R process to make these weak points more durable and increase the service life of the hydraulic cylinder. The advantages of the process are measurable: up to 100% longer service life, 25% higher performance and weight and volume savings of up to 35% compared to conventional welded constructions can be achieved by using deep-R.

Bolted ring connections

The connection between the cylinder base and the cylinder tube can be made using bolted connections. The bolted connections transfer the axial compressive force of the cylinder to the base. In order to design screw connections safely in terms of calculation and construction, the forces and deformations at the screw connections and at the clamped parts must be examined precisely. The ‘VDI2230’ is fundamental to this investigation and these calculations.

Threaded connections

In this design, a large internal thread is machined at the end of the cylinder tube. The head or base of the cylinder is screwed into the tube using a matching counter thread. Machining the cylinder tube is straightforward and can be done entirely on a lathe. The disadvantage of this connection is possible work hardening or corrosion in the thread. Under certain circumstances, this can make non-destructive disassembly impossible. Maintenance of these cylinders is complex and expensive.

Conclusion: Consistent planning is important

Whether in wind turbines, injection moulding machines or mobile cranes, the performance of a hydraulic cylinder depends on its design. Precise coordination of the piston, rod, sealing system and material quality ensures precise movements and low friction losses.

Equally important are the connection technology between the tube and the base and the chosen design. Welded cylinders score points for their compactness, while bolted designs are easy to service. Innovative technologies such as our deep-R process eliminate design weaknesses, demonstrably double the service life and save weight.

If these factors are consistently taken into account during the planning phase, the result is a cylinder that works reliably over the long term, reduces maintenance costs and noticeably improves the overall cost-effectiveness of the machine.

Do you need a hydraulic cylinder and are currently in the middle of the planning phase? Benefit from ACONA's expertise: we provide individual advice and show you a direct comparison of customised hydraulic cylinders vs. standard cylinders to determine which solution best meets your technical and economic goals.