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Piezo-controlled valve controls very-high-speed air turbine

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A piezo-controlled pressure regulating valve from Hoerbiger-Origa is helping scientists examine matter at an atomic and subatomic level by controlling rotational speed in a nuclear magnetic resonance chamber built at Bruker BioSpin in Rheinstetten, Germany.

Piezo-controlled valve controls very-high-speed air turbineNon-destructive analysis of materials is a key technique for scientists working in a wide range of fields, with much of the current work being conducted at the atomic level. Bruker BioSpin has developed a system for nuclear magnetic resonance (NMR) analysis in which a sample container, supported on an air bearing, is turned using precision blasts of air.

During the design stages the Bruker engineers undertook an extensive search for a suitable high-performance valve and found only one that met all their criteria, namely the Tecno proportional valve made by Hoerbiger-Origa.

NMR works on the same principle as the medical procedure of magnetic resonance tomography. A very strong magnetic field is created within the chamber and radio waves are directed through it. This affects material in the chamber by transferring atomic nuclei to different energy levels as they absorb the radio waves. Different substances absorb different frequencies, so can be identified by their ‘resonance frequency’.

Because of the magnetic field, conventional electric motors cannot be used in this application and, due to the high rotational speed, an air bearing is the best option for supporting the rotor. These two factors combine to suggest that an air motor may be the best prime mover for the system. However, few air motors are able to offer the precision required.

Blast-driven turbine

The Bruker team found the answer in using Hoerbiger-Origa’s Tecno piezo-controlled air pressure regulator to drive an air turbine with precise blasts of air. Proportional pressure control is achieved using a tiny piezo ceramic lever that is bistable under the effect of a nanovoltage signal. One of its main attributes to Bruker is that its switching is practically instantaneous, so it gives very good control of the air flow. Another is that the nanovoltage does not adversely influence the magnetic field.

In fact the chamber also uses a second Tecno valve, this time for controlling the air bearing in relation to the total mass of the rotor plus its testpieces. A test procedure may involve several hours of operation, during which the rotor may be turning at up to 65,000rps (3.9Mrpm). Part of the design brief was such that the Hoerbiger-Origa valve must control movement to +/- four revolutions.

Ray Barnes, Hoerbiger-Origa’s UK Managing Director, says the company is no stranger to such projects: “We have equipment at other high-level research establishments in the UK; the performance requirements are almost always astonishing to those of us from an industrial background, but the extreme demands help us to raise performance specifications for our standard equipment and to extend the limits of the products' capability.”

 
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