Concrete piston pump

One firm turned wheezing, asthmatic pumps into the spoutitng high-volume booms of today.

- PUMP UP THE JAM: Karl Schlect developed a new kind of concrete pump that is helping add extra height to buildings everywhere.
- PUMP UP THE JAM: Karl Schlect developed a new kind of concrete pump that is helping add extra height to buildings everywhere.

One firm turned wheezing, asthmatic pumps into the spoutitng high-volume booms of today.

There's hardly a building site in the whole GCC that would be financially possible were it not for the invention of the 'placing boom', or concrete pump to give it a common name.

However fifty years ago, these devices were inefficient.Early pumps all worked on the 'peristaltic' principle, which means that a roller on an eccentric cam would squeeze the pipe together, thus forcing the mixture along it in the same way that toothpaste is squeezed out of a tube.

There were advantages to this system - the most notable being that no part of the machinery needs to come in contact with the mix as the concrete stays in the pipe until placed.

The disadvantage however is that only a low pressure is possible using this method, meaning that the concrete could not be pumped very high. Also the hose had to run at pressure in order to get a continuous supply from the hoper, leading to mind-bending problems involving seals.

This problem vexed a young German engineer named Karl Schlecht. In 1958 he had started a business making plastering machines based from his father's garage. Ten years, and many happy customers later he started to work on a concrete pump that would offer higher volumes.

This time, unlike the market launch of mortar pumps, Putzmiester was not the "inventor", but was in competition with established manufacturers from the outset.

Their concrete pumps had often reached their limits - for reasons inherent in the system. Higher pressures, larger pump volumes and a more even concrete delivery were only possible, in Schlecht's opinion, if previous design principles were thrown out.

The way to do it, the engineer reasoned, was to build a piston pump. The idea wasn't new, but it had previously been impractical for concrete pumps, as the valves stuck solid very quickly.

However, the firm's R&D department came up with a twin-cylinder piston pump combined with a special 'flapper' valve system that allowed for record pressures and heights.

Conservative German buyers took some convincing though. Only when the world record was broken in 1977 Putzmeister finally gained acceptance in the construction industry.

Since then the firm has become one of the few recognised names in pumping concrete, and its booms have reached dizzying heights.

In December 2007, Schlecht, who still enjoys his job, switched on the pumps at the Burj Dubai, where the concrete was pumped to 601 meters - another world record.

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