Metering pumps solve turbidity testing dilemma for Welsh Water 20 March 2013

Watson-Marlow's new Qdos 30 metering pumps have taken over from bellows pumps for turbidity testing at the Pontsticill water treatment works in the Brecon Beacons National Park.

Plant engineers knew that the introduction of air into the samples, using the old pump technology, was not only undesirable but also led to false readings.

Marek Cegielski, a process scientist and manager at Dwr Cymru Welsh Water, says that the new metering pumps not only provide excellent suction lift, but also do so without air locks.

"In the past we've tried other types of turbidity monitoring devices, such as dip probes, but without much success," he says.

"We've even used bubble traps in conjunction with our bellows pumps, but we still fell short of 100% reliability," he continues.

"Eliminating bubble traps was one of the attractions of replacing one of our bellows pumps with the new Qdos 30."

The new metering pump is now taking elutriant from a DAF (dissolved air flotation) filtration plant – after coagulation, flocculation and flotation – and lifting it three metres before it passes through a turbidity meter and returns by gravity back into the flow.

"Our main requirement is for a constant, pulse-free flow," says Cegielski. "Previously, we had tried fitting back valves to bellows pumps to stop the pulsing but, in truth, we couldn't properly buffer the effect and still ended up with false readings."

Watson-Marlow's Qdos 30 metering pump was installed in July 2012, and has been working well ever since, without any signs of air introduction or flow variation, he says.

"So far, so good, as far as we're concerned – when new technology comes along that has a clear advantage over existing market solutions, then we are always willing to give it a try," states Cegielski.

"In total we have four streams to monitor at Pontsticill, so, if our existing Qdos 30 continues to meet expectations, then we'll place an order for a further three pumps."

Brian Tinham

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