Demanding role for diaphragm pumps

Energy Pumps has just been awarded single source framework supplier status for diaphragm pumps for Scottish Water. Sales manager Heath Waring looks at some of the issues facing the utilities in selecting the correct pumping solution

Capital cost is no longer seen as the key procurement factor when selecting the correct pumping solution. Energy conservation, low maintenance, and health and safety are now some of the key factors when looking at the transfer of wastewater and slurries.

Pumping is integral to virtually all processes in the wastewater industry: settlement of solids, aeration, sludge digestion, sludge mixing and advanced sludge processes such as sludge pasteurisation all require pumps to transfer the fluids around the plant. And the main pump types currently in use are progressive cavity (PC), positive displacement lobe and centrifugal type pumps.

Having the correct pump for the duty is no longer just down to how well it pumps, but how energy efficient it is over its life span. Manufacturer Energy Pumps says its diaphragm pumps are currently providing up to 50% savings on installed power over many competitors, which can slash energy costs.

The main advantages for engineers and site operators working with diaphragm pumps are the simplicity of design and robustness of the construction. The pumps can self-prime up to 6.5m, handle grit-laden and raggy sludges of up to 15% dry solids, and deliver heads of up to 60m (dependent on drive type and valve arrangement). This type of pump will dry run indefinitely without damage to any of its parts. And in most cases there are 12-month warranties on the pump and the wear parts and consumable parts, such as the non-return valves and diaphragm. This means that, for the first time, pump users can accurately budget for their maintenance spend for year one.

One of the limiting factors for diaphragm pumps used to be low flowrate, from 0.5l/s to 3 l/s, which was fine for general desludging duties. But Scottish Water required a new range of diaphragm pumps to actively compete against PC, lobe and peristaltic pumps on higher flow duties

In February 2006, Rene Clarke, managing director of Energy Pumps made a key commercial decision to design, build and add two new diaphragm pumps to the range, one of which is now available offering flows up to 10l/s and heads up to 60m. In the autumn, Energy Pumps will be launching the Manta, this will be one of the largest (if not the largest) single-acting diaphragm pumps in the world, with flows up to 35l/s and delivery heads up to 60m.

The full range of diaphragm pumps will also be available as trailer or trolley-mounted units to enable Scottish Water to use them for heavy-duty pumping in emergency situations. These pumps will be driven by high-quality Yanmar electric-start diesel engines, which have proven themselves to be the right engine choice for quality and reliability.

Typical applications for Energy Pumps' diaphragm pumps include desludging of primary, humus and final settlement tanks, return-activated and surplus-activated sludges and humus sludge return, digester feed, sludge tank recirculation and transfer, and press feed.

The pumps can also handle a range of harsh or aggressive materials such as sand and grit, sodium hypochlorite, sodium bisulphate, ferric chloride, lime slurry, carbon slurry, sodium hydroxide, potassium permanganate, aqueous ammonia, alum, methanol, oil slurries and a range of polymers.

This is dependent on pump casing and elastomer suitability, and has the ability to demonstrate that this flexible and inherently simple pumping technology represents a genuine lowest whole-life cost option to Scottish Water. And it means that Energy Pumps' units are increasingly being chosen over conventional pumping solutions.

The hard solids limitation is governed by what will pass through the non-return valves. In most cases, the company uses its 100mm Mallard Valve, which can pass hard solids up to 70mm. But it has been known to pass crushed tin cans, golf balls, broken glass and stones without damage to the non-return valves or diaphragm.

The simple reciprocating action of the diaphragm, which can be electrically, hydraulically or diesel-engine driven, provides a gentle pumping action, which is well suited to sludges that are dosed with flocking agents or for prevention of rat holing during desludging. Where high heads above 40m are required, the rubber non-return valves are replaced with ball valves - as the rubber valves have the potential to collapse. Ball valves will still provide high solids passage while allowing the higher delivery heads and years of trouble-free use.

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