With regard to the EU Machinery Directive, hydraulic control systems must be designed in such a way that the risk to people and to the environment is as low as possible. This implies that the machine or the drive installed in it must, in addition to its technical function, also meet the safety level specified by the risk analysis.
In hydraulic systems, such control functions are realised with the help of electronic controls in combination with hydraulic blocks. The required valves are compactly housed in control blocks.
Directional valves, especially control valves, always leak due to their design. This is not relevant during operation, as the pressure supply provides sufficient volume flow. However, to prevent a cylinder from sinking under load in a pressureless state when installed vertically, lines A and B to the cylinder must be shut off separately.
Preferably, shut-off functions are integrated directly into valve plates and mounted directly onto the cylinder. This means that no hose connection is necessary between the valve block and the cylinder. Thus, the cylinder cannot sink even if the complete power supply fails or the hydraulic lines are damaged.
If leakages are to be expected in the hydraulic cylinder, e.g. due to functional oil of a floating gap seal, the functional oil lines must also be shut off separately accordingly.
In the case of hydraulic cylinders with throttle gap seals on the piston or hydrostatic bearings, this measure against sinking is not sufficient. Other precautions, such as a clamping unit, must be implemented here.
To prevent the piston rod, which is installed vertically downwards, from sinking, it is sufficient to shut off the rod side line. Shutting off both sides increases safety, however, as no pressure can then be applied on the piston side.
In combination with a safety control system, a performance level according to EN ISO 13849-1 up to PLe can be achieved by connecting two shut-off valves in series. In this case, the shut-off valves must be integrated into the control system with position monitoring according to EN ISO 13849-1 and the control system itself must meet the required safety standard.
Control block with shut-off function A-B for PLe
Especially in switch-on mode, a machine must have the possibility to move each drive axis in reduced speed. Depending on the requirements and risk assessment, it may be necessary to perform this setup circuit as a safety function. For this purpose, a fixed throttle or a throttle that cannot be adjusted without tools and is also suitably secured shall be used in the control block.
Control block with shut-off function A-B for PLe with reduced speed due to fixed throttle
In this circuit example of a control block, the flow required for the application with PLe in operation is separated by two shut-off valves V1 and V2.
Parallel to this, a bypass is set up with the shut-off valve V3 and the throttle V4, which provides a reduced flow for the switch-on operation.
Somit kann der Antrieb mit einer durch die Drossel sicher reduzierten Geschwindigkeit verfahren werden. Je nach Anwendung und Sicherheitserfordernis kann ein weiteres Sperrventil V5 notwendig sein, das die Drossel V4 mit dem Sperrventil V3 umschließt.
The Hänchen switch-on block is a standardised valve block with integrated functions:
|Port P||Port T|
|3||250||G1 ½||G1 ½|
The control block is made of galvanised steel and rated up to 280 bar.
The control block can be extended for further functions or designed in redundant form for applications with performance level up to PLe.