WET News

MAY 20 WET NEWS 21 Ita culpa ex et et imporem dolut ut fuga. Picatia cullesto quiate quia parch A solution: Pump-attuned valves improve energy efficiency E ver since KSB was founded it has been designing and producing a wide diversity of valves. One particular model was known for closing so soly and reliably that it became the valve of choice for use in the ex- haust systems of numerous die- sel-electric submarines. Its job was to keep seawater out of the exhaust systems of snorkeling subs. So what could have been more logical than to use Serie 2000 check valves, with their dual plate valve disc, for less spectacular applications, too? The robust, maintenance-free valves have one-piece cast bodies with high mechanical strength and excellent corrosion resist- ance. Their spring assembly ensures reliable seating in situa- tions where gravity alone would not suffice. This type of valve can be installed horizontally or verti- cally with no special tools required. A wide spectrum of materials allows service at tem- peratures between -196°C and +538°C. Their main merit, how- ever, is their low pressure loss coefficient. The valve disc opens stably even at very low flow velocities. Field data In order to closely analyse the opening behaviour of Serie 2000 valves, extensive tests were per- formed on one of KSB's own test stands. The basic goal was to examine which kind of check valve – dual plate check valve or li check valve – is most suitable for which kind of application. Both types were therefore tested in diverse situations. In the first test set-up, the technicians installed a li check valve with no flow stabilisation section. The results agreed with practical field data. At minimal volume flow, the opening behav- iour was unstable, and the valve began to chatter. At maximum flow, the spring vibrated strongly due to the high velocity of flow through the valve. Even the sub- sequent installation of a flow sta- bilisation section failed to improve that behaviour. In the second set-up, the tech- nicians installed a Serie 2000 dual plate check valve with, and then again without, a flow stabi- lisation section. This time, the observed opening behaviour remained stable, even with the valve in a partially open position, and there was no chattering like in the case of the li check valve. Models From 50mm To 300mm Selprime Auto Self-Priming Super Silent From 58db(A) Hydraulic Submersibles Electric Submersibles 24/7 Callout Branches Nationwide Selwood has been manufacturing, hiring and selling pumps for over 60 years. Please call for expert advice on all pumping applications. PUMP HIRE, SALES & SERVICE 08450 733835 www.selwoodpumps.co.uk UK's No1 Pump Hire Specialist The Public's View of a Changing Sector We are entering into a period of enormous change. The proposed Water Act, mandatory water meters, increasing customer choice and various environmental challenges are combining to create an uncertain future. Many of the proposed changes are being carried out in the name of the public interest, but how informed (or indeed interested) are the public? We commissioned a report in order to answer that question and help frame the debates that will be concerning the water sector in future months and years. View the report at www.talis-uk.com We have done the research... Any unsteady behaviour of the dual plate valve discs was reme- died by installing a flow stabili- sation section. Loss coefficient Under low flow conditions, the li check valve remained very unsteady despite installation of a flow stabilisation section. Conse- quently, such valves should only be installed in cases where space constraints leave no room for any other choice, because its unsta- ble opening behaviour can, under certain circumstances, result in a very high rate of wear. Nor is this kind of valve inher- ently suitable for use with a fre- quency inverter. This is also evi- denced by a comparison of head losses calculated for both types of valve. The individual loss coeffi- cient, ζ, of a wafer-type li check valve is approximately 4.5. With a Serie 2000 valve, the situation is intrinsi cally more favourable because there is no change in the direction of flow in the valve, so its ζ value, at 0.4, is much better. This can also be demon- strated by way of the head loss, Hv, as calcu lated according to the following equation. DN 200 mm pipes were selected on the basis of assumed flow velocities of v = 1 - 1.5 m/s on the suction side and v = 2 - 2.5 m/s on the dis- charge side. Applying these data, the equation , yields 1m as the head loss attributable to the li check valve. The same equation yields a head loss of just 0.08m for a Serie 2000 valve. Depending on the application in question, this could mean that a smaller pump could be installed. To ensure stable, vibration- free behaviour of the closing ele- ments, though, even dual plate check valves need a flow stabili- sation section measuring about 5 x DN. This helps ensure smooth and energy-efficient pump oper- ation under any set of load conditions. It pays off to take a holistic view of the valve, the pump and the frequency inverter as a sys- tem. The cost of installing a new valve redeems itself very quickly. Of course, optimal matching of pump and valve is not the only way to reduce energy expendi- ture. No matter which measures are taken, though, the decisive factor is to ensure that the system is designed to match the operat- ing point. n

• Cover