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FEATURE PNEUMATICS & HYDRAULICS The block approach to hydraulics


Thanks to the benefits offered by bespoke hydraulic control blocks, more and more applications are adopting the approach. Gerhard Ruppel, founder and managing director of Gerhard Ruppel Hydraulik, explains


T


raditionally, the valves used in hydraulic circuits are positioned


around the circuit at points where the fluid flow needs to be controlled. Increasingly, however, most if not all valves are being grouped together in one place on a single block. The applications that are suitable for the control block approach range from presses, through construction machinery to deep-sea drilling rigs.


THE APPROACH There are many benefits to the approach, even though the pipework that makes up the circuit has to be routed through the block. For a start, the block has a small footprint, the risk of leaks is low, the screw-in valve technology is easy to maintain, and both standard valves and tailored solutions can be used. In addition, energy and flow optimised systems can be incorporated during the block development stage, and a block with screw-in valves has aesthetic appeal when compared to a traditional hydraulic control with pipes and connectors. One area which is already adopting


this approach is mobile hydraulics, partly because such applications have space restraints, ensuring power density and long service life under unfavourable environmental conditions (vibrations, fluctuations in temperature, corrosive media, etc.). In addition, installation time for the hydraulics is reduced. A typical project may involve the design of a control block with more than 50


valves for the control console of an item of construction machinery. Pipework design for a control console of this size would be considerable and its installation would require around two person-weeks to complete. In contrast, a block solution would produce a control desk of less than 1m long which could be connected up by one fitter within a day. Another example took place during development of a new type of cement mill where the designers had to implement a hydraulic safety system. If a very large piece of rock has to be processed, the gap in the crushing gear has to be enlarged in a very small space of time to prevent the rock material damaging the crushing rollers and/or their drive. As conventional pressure limiting valves would not react quickly enough, a control block was developed incorporating a pressure limiting valve from the Sun Hydraulics range which has a fast reaction time. As a result, the adjustment drive is able to react very quickly – within 300 msec, the system flow increases from 100 l/min to 1000 l/min without any pressure spikes. All the functions required by the


machine manufacturer have been incorporated in a compact, application- specific block which is also reliable under the harsh environmental conditions faced. Control blocks have also been used by a


Russian press manufacturer, where a block was developed with three NG25 directional control valves and four NG10 valves, as well as other components. The block uses


PUMPS SUIT ADDITIVE INJECTION


As a manufacturer of solutions for the storage, transfer and distribution of liquid and gas products, Flotech Performance Systems provides additive and dye injection skids for petroleum and chemical applications. These range from injection hardware skids through to full turnkey systems and can include additive storage, secondary containment pipework, pumps and pump control. The pump used in many additive applications ensures they generate sufficient differential pressure for the additive to be injected efficiently and smoothly into the main process line. Here, the operation of the pump and how it is controlled is crucial to skid performance. Duty/standby pump systems will be controlled to provide alternate


both proportional and on/off control valves. With the new system, pressure build-up to initiate press movement is rapid, and the block also manages pre-charging and pressure sequencing. Another example was where a German research ship had been equipped with a hydraulic drilling unit designed for drilling the seabed at a depth of 2,500m. The first challenge was to ensure compensation of the external pressure of around 250 bar and reliable separation of the hydraulic circuit from other media such as drilling fluid and sea water. The electrical signals generated at


the control desk on the ship are converted by the hydraulic block into movement at a depth of 2.5km. Here too, both on/off and proportional valves are employed, and pressure regulation is used to adapt the hydraulic circuit to the requirements in question.


Gerhard Ruppell Hydraulik www.ruppel-group.de Enter 210


operation and to also start the standby pump if needed. They may need to cover flow ranges up to 160 l/min and differential pressures as high as 16 bar. The pump may also need to be ATEX certified. To meet application demands, the company has selected the Viking


SG Series External Gear pumps which are supplied by Michael Smith Engineers. These spur gear design external gear pumps are able to pump low volumes of liquid at high differential pressures, providing smooth, accurate output which can be easily monitored and adjusted, resulting in process consistency without wastage. The SG pumps are available in 29 sizes for capacities up to 45m3


/hr at differential pressures to


172 bar and operate on liquids with a viscosity range of 1.0 to 250,000 cSt.


Michael Smith Engineers www.michael-smith-engineers.co.uk Enter 211


Even under challenging conditions, control blocks work reliably with minimum maintenance requirements


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SEPTEMBER 2014 | DESIGN SOLUTIONS


/ DESIGNSOLUTIONS


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