The Gravejo (Poland) plant of particle board manufacturer Pfleiderer was too frequently replacing high-pressure pumps on its production lines. The pumps play an essential part in the main continuous production process, delivering resinous glue to nozzles where it is sprayed on to the wood fibers.
The problem faced by Pfleiderer will be familiar to plant engineers throughout the board industries and beyond, wherever abrasive materials have to be pumped at high pressure. Most pumps capable of delivering these pressures rely on dynamic seals and are always vulnerable to excessive wear. In this case the pumps originally installed were gear pumps, chosen for their high-pressure capability; the resin must be pumped to the spray nozzles at a pressure of 80 bar.
But soon the gear pumps ran into difficulties. There were problems with mechanical seals, which began to leak. Moreover the pumps were not easy to clean. Particles of hardened resin became trapped between closely meshing gears and damaged them. A pump and gearbox on one system had to be replaced three times within months.
The company had no confidence that other gear pumps or piston-type pumps would do better, but pump specialist Verder Polska was able to suggest an alternative. The pump Verder recommended, the Wanner Hydra-Cell, can operate continuously at the high pressures required, and its design is seal-less. The drive mechanism is totally isolated from the pumped liquid by hydraulically-balanced flexible diaphragms, which also perform the pumping action. There would be no problems with seal leakage or hardened resin, and in any case the pump can handle abrasives and solid particles up to at least 500 µm in size, as well as chemicals, corrosives, viscous liquids and thin non-lubricating fluids. It can also run dry without damage.
Pfleiderer engineers installed their first Hydra-Cell (model G35) pump in 2005. Six months later, with no problems reported, the company bought a second G35 for the same application. Working at 80 bar, and driven by 18.5 kW motors, each of these pumps delivers resin to the spray bars at 100 l/min. Encouraged by their performance, Pfleiderer has subsequently installed smaller Hydra-Cell (G10) pumps on another system, pumping ammonium nitrate. On this application the pumps have replaced a larger, more expensive piston diaphragm pump. They deliver the required flow smoothly, with lower pulsation than the original pump.
None of the Hydra-Cell pumps have so far needed repair or replacement. Routine maintenance comes down to an oil change every six months and a yearly check on valves and diaphragms. If they need replacing, the work can be carried out in two hours or less, without taking the pump out of the line.
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