Mill type cylinders
Due to their robust design, mill type Hydraulic cylinder are also suitable for use in applications with extreme operating conditions.
Tie rod cylinder
In tie rod Hydraulic cylinder the top of the cylinder, the cylinder tube and the bottom of the cylinder are all connected together via a tie rod. The main feature of a tie rod Hydraulic cylinder is its especially compact design.
Hydraulic cylinder with spring return, single acting
Hydraulic cylinder with spring return are single acting Hydraulic cylinder. They are used in applications where an external, restoring force does not exist. Return springs may be situated either within the cylinder or mounted onto the cylinder as a separate component. As these springs can only carry out limited strokes and exert limited forces, they are mainly to be found in “small cylinders”.
Double rod cylinder
Double rod cylinders have a piston firmly fixed to two piston rods of smaller diameter. The maximum force that can be transmitted depends in both directions on the same annulus area and also on the maximum permissible operating pressure.
This means that at the same operating pressure equal forces act in both directions. As the areas, stroke lengths and therefore also the space to be filled are the same on both sides, it follows that the speeds will also be the same.
For special applications there are versions of double rod cylinders with different piston rod diameters. With these types the forces and speeds act similarly to single rod cylinders in the relationship of the sizes of the two annulus areas.
Telescopic cylinders vary from “normal” cylinders in that they only require a very small amount of space for installation in the retracted position in comparison to “normal” cylinders with the same stroke.
If the pistons are placed under pressure via port (A), the sections extend one after another. The pressure is dependent on the size of the load and the effective area. Hence the piston with the largest effective area extends first. At constant pressure and flow the extension begins with the largest force and the lowest speed and finishes with the smallest force and the highest speed.
In double acting cylinders the pistons are extended in the same way as in single acting cylinders. The order in which the individual stages are retracted depends on the size of the annulus area and on the external load. The piston with the largest annulus area returns first to its starting position.
Telescopic cylinder, double acting
Telescopic cylinders vary from “normal” cylinders in that they only require a very small amount of space for installation in the retracted position in comparison to “normal” cylinders with the same stroke. In double acting cylinders the pistons are extended in the same way as in single acting cylinders. The order in which the individual stages are retracted depends on the size of the annulus area and on the external load. The piston with the largest annulus area returns first to its starting position via pipe port (B) when it is placed under pressure.
Rapid traverse cylinder (cylinder for rapid traverse)
With this type of cylinder, as long as not the whole working force is required, only part of the effective piston area,the so-called rapid traverse piston is pressurized. The total effective piston area is connected later to the hydraulic pump, by the response of pressure valves or limit switches. The advantages are as follows: high rapid traverse speed due to low volume of fluid and high compression force due to a large effective piston area. Rapid traverse via connection port A1; compression force via connection port A2; return travel via connection portB.
In double acting cylinders operating in tandem, there are two cylinders which are connected together in such a way that the piston rod of one cylinder pushes through the bottom of the other cylinder to its piston area. By using this arrangement the areas are added together and large forces may be transferred for relatively small external diameters without increasing the operating pressure. However the longer length of this model must be taken into account.
Plunger cylinders are used wherever a definite direction of force will ensure a return of the piston to its starting position. Examples of this are upstroke presses, lifting devices, etc.Retraction of the piston can only occur through the weight of the piston or due to an external force being applied.
End position cushioning
The end position cushioning is a device on the hydraulic cylinder, which is used for reducing the speed of a piston before reaching its end position. This cushioning may be fixed or adjustable, mechanical or pilot operated.
The piston (1) is fixed on the piston rod with the damping bush (2). The inward travel of the conical damping bush into the bore of the cylinder bottom (3) reduces the cross section for the fluid draining out of the piston area (4), until it eventually reaches zero.The fluid from the piston area can now only flow out via the bore (5) and the adjustable throttle valve (6) where there is cushioning. The smaller the flow cross-section, the greater the cushioning will be.
Mounting elements for hydraulic cylinders
More than 50 % of applications use swivel clevis or plain clevis mounting at the cylinder cap end. In addition to these types, the following methods are quite common : Piston rod eye with swivel or plain bearing, flange on the cylinder head or cap end, trunnion at the cylinder head, cap or centre, and foot mounting.
(2) Plain clevis at cylinder cap
(3) Flange at cylinder head
(4) Flange at cylinder cap
(5) Trunnion at the centre of the cylinder
(6) Foot mounting