The Variflow pump range has been extended with a hygienic self-priming pump series called TPS, based on the standard priming TP series of centrifugal pumps. The hygienic self-priming pumps work as quietly as their conventional centrifugal counterparts and provide good flow properties as well as optimum CIP capability. Further benefits are low power consumption, ease of mainte-nance and minimal sensitivity to hard particles in the product flow.
Although liquid ring pumps basically do an excellent job, they also have a few disadvantages. The noise emissions, less-than-perfect hygiene and relatively poor control behaviour of this pump type are the most important criticisms raised by customers operating hygienic applications. To satisfy future demands from the markets, GEA Tuchenhagen has developed the Variflow TPS series. The manufacturer has not only succeeded in eliminating the shortcomings of the liquid ring pumps described above, but has also added extra benefits such as low power consumption, ease of maintenance and minimal sensitivity to hard particles in the product flow. The last-mentioned point, in particular, often led to serious damage to liquid ring pumps during the first hours of operation after commissioning – notably from welding beads. The main fields of application are CIP return lines, product conveying and tank discharge. However, the hygienic self-priming TPS series also represents an attractive alternative for other pumping tasks, where ordinary priming centrifugal pumps are unsuitable due to the high gas content and liquid ring pumps cannot be used on account of their high shearing forces.
The self-priming Variflow TPS series is based on the standard priming TP series of centrifugal pumps. A so-called screw rotor device is fitted upstream of the suction side of the TP series. The rotor is simply screwed onto the pump shaft in place of the impeller nut. The rotor housing is welded eccentrically to the pump cover and ends in the pump’s horizontal suction connection. If no gas is entrained in the medium to be conveyed, the TPS series works practically like a typical centrifugal pump. If gas bubbles enter the suction connection of the upstream screw rotor stage, a liquid ring is formed by centrifugal force and the gases collect in the centre. The liquid ring seals off the rotor blades externally against the rotor housing and at the upper edge of the rotor hub. This prevents enclosed gases from flowing back. Due to the eccentric configuration of the housing, the gases are centred beneath the hub and transported through the pump by the rotor blades. A recirculation pipe fitted outside of the pump ensures that liquid is constantly recirculated to the rotor housing, thus maintaining the pump’s suction capacity even if only gas is conveyed for a long period of time. Suction lift with evacuation of the suction piping is also possible.
Benefits of the pump series
Whereas liquid ring pumps create a noise similar to a turbine, the TPS series works as quietly as a conventional centrifugal pump. The generous design with good flow properties results in optimum CIP capability. The impeller of the TPS series can be reduced according to the operating conditions to achieve optimal pump characteristics. The TPS series also enables operation with a variable frequency drive over the entire capacity range. Its hydraulic efficiency is almost equivalent to that of ordinary priming centrifugal pumps. In the low flow range, the motor for the TPS series can usually be one, if not two, sizes smaller than for a liquid ring pump. Maintenance is similar to the TP series and the wearing parts are identical. Only an additional O-ring is required to seal the rotor housing cover. New pipelines that have not been properly rinsed can contain hard metal particles such as welding beads. The TPS series has extra-large gaps that make the pump less sensitive to this kind of impurity. The shearing forces of the TPS series are only slightly higher than for the TP series, which already has optimal flow properties.
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