Case studies

Effective cooling for computer tomographs

Would you put 36-times your body weight on your chest? Hardly imaginable! Find out how modern circulation pumps handle these forces.

Imaging techniques play an indispensable role in medicine. The technology is becoming increasingly complex in order to support doctors in diagnosis and therapy with images of the highest possible resolution - for diseases as well as in cancer medicine. The demands on computer tomographs (CT), for example, are high: in addition to optical quality; high robustness, reliable operation and patient safety are required at all times. In the construction of circulation pumps for CT cooling, the Austrian manufacturer KRAL relies on plain bearings and sealing rings made of silicon carbide (SiC).

During surgeries, the X-ray tubes in computer tomographs develop high temperatures. This makes permanent cooling necessary. KRAL has developed special screw pumps for this purpose, which are integrated directly into the motor housing and deliver the coolant to the X-ray tubes in the CT system. The pump and motor form a single unit, and the motor shaft also serves as the pump shaft. Thanks to its compact design, the system is located directly in the dector ring.

High centrifugal forces in CT operation

During imaging, the dector ring rotates around the patient, generating high centrifugal forces of up to 35g. This demands real top performance from the pump system: It must be manufactured with high precision to reliably achieve the required flow rate under all operating conditions. In addition, the pump must be able to be switched off and on at any time, even during rotation. Centrifugal pumps, for example, cannot meet these requirements. Screw pumps such as those from KRAL, on the other hand, permit space-saving and at the same time provide a highly reliable solution. The coolant used is a water-glycol mixture that has a low viscosity. KRAL engineers have opted for a special coating of the pump housing, which allows even low-viscosity media to be pumped with high efficiency.

Technological advances mean that the demands placed on imaging processes are constantly growing. A rule of thumb is: the higher the achievable rotational speeds in the CT system, the better-resolution images are possible. Miniaturisation is also advancing, and the weight and installation space of the motor and pump system are being continuously optimised. The aim is to make all components even more compact, while at the same time increasing forces are acting on the pump's plain bearings, among other things.

Technical ceramics for pump bearings

In order to meet all the requirements for robustness and reliability, KRAL decided to use SSiC grade technical ceramics for the plain bearings after examining various alternatives. This high-strength, advanced ceramic material is almost as hard as diamond and therefore resistant to wear, chemicals and corrosion - even at high temperatures. The results are convincing: the pumps meet the target of 40,000 operating hours and more without difficulty, and since the use of the technical ceramic there has not been a single plain bearing failure. The solution is completely maintenance-free and is replaced after a defined running time, including the motor.

Durable and robust

Designing the solution, KRAL was able to build on its decades of experience in the development of screw pumps made for a variety of purposes including pumping crude oil distillates. The ceramic material was selected in close technical partnership with SiC manufacturer 3M. The result is a system that fully meets the various requirements of modern medical technology. For example, the design principle of the canned motor pump means low-noise output, making it a more patient-friendly operation. Not only is permanent cooling reliably ensured - at the same time, the canned motor pump as a hermetically sealed component ensures leak-free and safe operation at all times.

The quality speaks for itself: canned motor pumps from KRAL are in demand worldwide and prove themselves under the most difficult conditions. The Austrian family-owned company was founded in 1950 and has since focused on the development and manufacture of screw pumps and flow measurement technology. In addition to medical technology, the company has also focused primarily on the marine, power generation, oil & gas, mechanical engineering and chemical industries. KRAL GmbH has around 250 employees and over 40 sales partners worldwide. The export quota is an impressive 97 percent.

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