Hydraulic Cylinders

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Hydraulic cylinders convert hydrostatic energy into mechanical energy. They are considered as motors or actuators capable of producing work. However, hydraulic cylinders differ from hydraulic motors as they carry out a linear (translatory) movement instead of a rotary movement. Thus, the cylinders are also referred to as linear motors.

How Much Force Can You Get? See the Mathematics behind Hydraulic Cylinders

The maximum cylinder force F is dependent on the maximum operating pressure p and the area of the piston (effective area A). At constant pressure, a cylinder with a larger effective area A will produce a larger force F. At higher pressures, the force F will also be larger:

F = p • A [in kN]

You need hydraulic cylinders to perform certain types of work: for example, in applications such as those where loads must be lowered, locked, lifted or moved.

How DTA Can Help You:

DTA has considerable expertise with hydraulic cylinders and carries an extensive inventory of hydraulic cylinder spare parts and accessories, such as seal kits and linear transducers. Depending on your requirements, DTA can supply high-quality hydraulic cylinders, taking into account a wide variety of functional and system requirements.

DTA supplies all standard hydraulic cylinders from brands like Parker Hannifin and Bosch Rexroth. We also supply servo cylinder systems and custom-engineered cylinders from renowned hydraulic cylinder manufacturers such as Eaton Hydrowa and IHC Vremac.

Different Types of Hydraulic Cylinders

In hydraulic cylinders, two functional types can be distinguished: double-acting and single-acting cylinders. Only rapid traverse cylinders and telescopic cylinders are available as either single-acting or double-acting cylinders. Due to their function, it is possible to categorise hydraulic cylinders as below:

Single-acting Cylinders

• Push action cylinders
• Pull action cylinders
• Rapid traverse cylinders
• Telescopic cylinders

Double-acting Cylinders

• Differential cylinders
• Double rod cylinders
• Tandem cylinders
• Rapid traverse cylinders
• Telescopic cylinders

Single-acting cylinders have one effective area, located on the bottom side, which can exert force in one direction only. In most hydraulic systems, these are designed as plunger cylinders and an external force is used to return the piston to its starting position: e.g. lifting devices, upstroke presses, etc.

If there is no force to return the piston to its starting position, springs must be applied. This is only possible with small cylinders due to the limited force and stroke length of the return springs. Examples of spring return single-acting cylinders are assembly tools and installation work.

Telescopic cylinders are used in hydraulic lifting applications, or where large amplitudes are needed but limited space is available, e.g. tipper trucks. The single or double-acting differential cylinder is generally used in mobile and industrial hydraulic systems. The most common design principles of the hydraulic differential cylinder in tie rod and mill type design are discussed below.

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Tie rod cylinders are used in machine tools, the automotive industry, plastics machinery, transfer lines and other manufacturing devices. The main feature of the tie rod cylinder is its space-saving compact design, which makes it particularly suitable in manufacturing devices.

Key features of the tie rod cylinder:

• Compact design
• Wide mounting range
• Limited piston diameter
• Limited stroke length

The top and bottom of the tie rod cylinder, as well as the cylinder barrel, are connected together via four tie rods. Extended tie rods at the head or base of the cylinder may be used to mount the tie rod cylinder. Threaded holes and subplate mounting options are also included in the wide mounting range of the tie rod cylinder.

Typical parameters are:

• Nominal pressure: up to 200 bar
• Piston Ø: 25 to 360 mm
• Piston rod Ø: 16 to 250 mm
• Maximum stroke length: 2,000+ mm
• Maximum stroke speed: 0.5 m/s

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Mechanical engineering is the field of activity for mill type cylinders. They are used in mobile machinery, steel and iron works, civil engineering, presses, cranes, offshore applications and ship-building. The main feature of mill type cylinders is their robustness.

Key features of the mill type cylinder:

• Robust design
• High nominal pressure
• Larger piston diameters
• Long stroke length

The top and bottom of a mill type cylinder and the cylinder barrel are welded, screwed or tightly connected with bolts or retaining rings. Compared to tie rod cylinders, mill type cylinders have fewer mounting possibilities, however, standard mounting, such as clevis, flange, trunnion and foot mounting, are possible.

Typical parameters are:

• Nominal pressure: up to 350 bar
• Piston Ø: 25 to 450 mm
• Piston rod Ø: 14 to 220 mm
• Maximum stroke length: 6,000+ mm
• Maximum stroke speed: 0.5 m/s

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Servo cylinder systems are hydraulic cylinders with hydrostatic bearings. Hydrostatic bearings have low friction and are ideal in situations where high oscillation frequencies with small amplitudes are required. For example, materials testing devices and movement simulators.

Key features of a servo cylinder system:

• Low friction
• High dynamic response
• Accuracy
• High speeds

Servo cylinder systems are available with hydrostatic wedge cap bearings or with full hydrostatic bearings (cavity bearings). The type of bearings you need depends on the required speed of the hydraulic system in operation.

Typical parameters are:

• Pressure: up to 210 bar (with cavity bearings up to 280 bar)
• Force: 1 to 4,000 kN (up to 10,000 kN with cavity bearings)
• Stroke speed: 2 m/s (up to 4 m/s with cavity bearings)

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