9 - AHP Merkle GmbH

1 Basic information about hydraulic cylinders
1.1 Descriptions of the various types of cylinders
Differential cylinders
For hydraulic cylinders, a distinction is made between differential cylinders and double rod cylinders based on
their methods of operation. Differential cylinders generally have only one piston rod. This means that there are
differences in the size of the surfaces that determine the force generated and the speed of the piston. Under
the same pressure and fl ow conditions both the force generation and the speed of the forwards and return
stroke of the cylinder are distributed in accordance with the area ratio.
An additional distinction is made between single-acting and double-acting cylinders While single-acting hydraulic
cylinders have a pressure port on only one end, double-acting hydraulic cylinders have a port for both cylinder
chambers in order to be able to perform forwards and backwards motions. With single-acting hydraulic cylinders,
either the forward or return stroke has to be performed by an external force, such as spring force or gravity.
Double rod cylinder
Cylinders with a through style piston rod are called double rod cylinders. Unlike with differential cylinders, the
pressurized surface is the same size for both the forwards and return stroke. This means that the work with the
same conditions and in the same manner for both the forwards and return stroke. The amount of hydraulic
fl uid that should be introduced corresponds to the volume being displaced.
1.2 Types
Basic information about hydraulic cylinders en
Block cylinder (BZ)
A characteristic feature of block cylinders is their rectangular housing. This housing shape allows the implementation
of various mounting options. They can be operated with an operating pressure of up to 500 bar
(7250 PSI), and there are various options for sensing the piston position. For strokes greater than 200 mm
(7.87 inches) the housing has a cuboid shape; larger strokes are implemented using a tube between the cuboid
head and the bottom. The main area of application of block cylinders is mold construction.
Block cylinder with wedge clamp element / guide rod (BZK / BZF)
With these cylinders, a guide housing is fl anged to a block cylinder. This housing guides a hardened rod that
can be loaded with side forces. With the wedge clamp element (BZK), a bevel is created in the guide rod. This
can be used, for example, to for the clamping of workpieces. With the BZF, the guide rod is used as a guide
with the capability to absorb side forces, which with hydraulic cylinders normally has to be avoided.
Block cylinder with non rotating piston rod (BVZ)
These cylinders are available up to 250 bar (3625 PSI) and maximum permissible torques between 3 and 90
Nm (2.21 and 66.38 foot-pound force). This cylinder option is always advantageous when the piston rod –
and any tools that it moves – are not allowed to rotate.
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