Contributed by Marcel Stamber-Bur, Development – Industrial Valves, Thomas Daniel, Application Development – Industrial Valves, Lars Hauptmann, Product Division Marketing, Dr. Nora Nagele, Head of Product Division Marketing – all Hydac Fluidtechnik, GMBH, Sulzbach/Saarland
The requirements for machine tools with regards to energy efficiency and quality have increased continuously over recent years. They need to not only set clamping pressures precisely but also retain them over time without loss. Hydac has developed a new solution for this field of application: the new proportional pressure control valve in seat-tight design comes with intelligent closed-loop control and integrated electronics. The seat-tight design ensures that no leakage occurs when the pressure is set and thus lowers energy consumption. The on-board electronics set the required pressure precisely.
Intelligent valves from Hydac can be used in brake systems, machine tools, and paper and chipboard manufacture.
Hydraulic systems, such as the clamping hydraulics in machine tools, often use proportional valves for pressure control. In conventional proportional pressure control valves with piston design, internal leakage occurs because of the inherent clearance between piston and hole. As both piston and hole are subject to form and position tolerances because of the production methods used, the amount of clearance cannot simply be reduced: a range of a few micron is necessary. In combination with high pressures, even this small gap results in not inconsiderable leakage flows that make it impossible to maintain the pressure permanently without additional supply. This lost energy must regularly be returned to the system, for example by a pump or an accumulator. This results in higher energy requirements and entails additional challenges, such as higher noise emissions and more space being needed for the components.
One way to reconcile the conflicting objectives of proportional pressure control and energy efficiency is to use a seat-tight design. This involves a cone being pressed against a seat edge, forming a metal-to-metal seal and eliminating the gap. This design enables the valve to function without any internal leakage.
Comparison of conventional valves with the Hydac innovative smart valves.
Pressure control valves are a combination of pressure relief valve and pressure reducing valve. To realize this function, three hydraulic ports are typically needed in the valve (actuator port A, pump P and tank T). In pressure-reducing mode, the valve creates a pressure drop from P to A, setting the desired pressure in A. To reduce the actuator pressure, the valve opens the flow path from A to T, thus functioning as a pressure relief valve. Conventionally, this pressure control is realized by a piston that controls the connections from P to A and from A to T. As described earlier, this design results in internal leakage in the valve. A balance of forces between the surfaces of the valve piston that are exposed to pressure and the spring or solenoid forces causes the desired pressure to be set. This also means that the design is limited to a small number of pre-defined pressure ranges, as a different piston diameter needs to be configured for each pressure range.
The valve electronics are located in an aluminum housing and are equipped with a type label and status LEDs.
With the P3DRSERE 6, Hydac has realized a pressure control valve with decoupled control edges in poppet design. The actuator pressure is measured by an internal sensor and compared with a nominal value by on-board electronics. This comparison of nominal and actual values represents a closed-loop control system. If the values differ, the electronics will either open the connection P to A, if the actual value is too low, or A to T, if the actual value is too high. If the comparison values reveal a difference that is within the permitted error tolerance, both control edges are closed and the set pressure is maintained without leaks. This happens even in the event of an error, e.g. power supply failure or cable break. In a machine tool, for example, this means that the workpiece will remain clamped safely in place if an error occurs.
Pressure control valve with actuator (A), pump (P) and tank (T) connections; function and closed-loop control are explained in the text.
As standard, Hydac supplies the valve with three controller pre-settings (slow, medium, fast). As the pressure control is highly dependent of the specific application, the customer is able to adjust the controller parameters. Software has been developed especially for this valve with a graphic interface that enables individual adjustments to be made to suit the application. For instance, the pressure rating can be defined in accordance with the desired use. The valve is connected to the computer via a standardized Micro-USB port. LEDs show the user the valve status. The on-board electronics are available in an analog design or IO-Link version.
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Filed Under: Components Oil Coolers, Valves & Manifolds
