Water & Wastewater Treatment Magazine
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www.wwtonline.co.uk | WWT | AUGUST 2017 | 25 FACTFILE: ARCHIMEDES SCREW PUMPS process could take place. This involves rotating the screw at reduced speed and adding screed. Eventually, the trough is created with an optimum gap of 6 mm between it and the screw ights, which provides maximum pumping e ciency. Dave Bennion, Project Manager at ECS said: "Our Midlands location allows us to service projects such as this across the country, from as far south as Taunton to the central belt of Scotland. Our dedicated teams bring great experience in Archimedean Screw Pumps to every job, which is an o„ ering that is unique to ECS. Our close working relationship with Landustrie ensures a reduced lead time on orders, while our fabrications division has the exibility to deliver almost any requirement." Furthermore, ECS o„ ers a full maintenance framework to support existing installations, with screw renovations, trough repair and bearing replacement all available to end users. Such attention can greatly increase the e ciency bene‰ ts of screw pumps, reducing downtime for operators. No screw pump installation is the same, so this integrated support framework o„ ers operators a one-stop- shop for all their screw pump requirements, no matter the variation in system. The screw pump off ers a very effi cient method of pumping water; low energy requirements and minimal cost of ownership ensure that long term operating costs are kept to a minimum. Modern designs allow fi sh to continue to migrate along the watercourse, thanks to the low rotational speed and wide openings between the blades. Landustrie has developed a special wristband around the outside diameter of the screw that rotates in the trough with minimal clearance. This unique design prevents damage to fi sh at the inlet where the blade and trough interfaces meet. In contrast, a centrifugal pump acts as a permanent barrier to fi sh migration. What disadvantages or drawbacks do they have? Screw pumps do not pressurise the water at all and cannot be used to pump water over long distances. The location of the screw pump is very important and compared to a centrifugal pump, they occupy more space. What diff erent types are available? The major diff erentiation between screw pumps is the type of trough in which they are located. The traditional What are Archimedes screw pumps and how do they work? Archimedes screw pumps are based on the ancient design of the Greek scientist Archimedes. They are still the most effi cient method of moving water over a short distance. The basic principle is an inclined tube, fi tted with fl ights or blades, slowly rotating inside a trough. Water at the base of the tube is carried by the blades up the trough and deposited at the highest point of the pump. Individual screws can be up to 25 metres long and inclined at a maximum angle of 40°. Based on a diameter between 250 mm and 5,000 mm a screw pump can be designed to li water up to a height of 12 metres, with a maximum fl ow of 12,000 litres per second. What applications in the water industry are they suitable for? The Archimedes screw pump is suitable for any location where there is a need to pump water over a relatively short distance. This can include inlet pumping stations or intermediate pumping stations in wastewater treatment plants, return sludge pumping stations, irrigation or drainage projects, reclamation of wetlands, stormwater applications, industrial processes, or even water rides in amusement parks. What are the advantag- es of this type of pump over other designs? The Archimedes screw pump off ers a simple and reliable method of pumping high volumes of water to a higher level. The open, clog-free design allows continuous operation, even when the water contains large particles or debris. The slow rotational speed of the screw means there is no opportunity for cavitation or undue wear. hand screeded trough uses the screw itself to create the exact clearance required for optimum effi ciency. Over time the screed is gradually worn away; this can be refurbished at the same time as the screw itself. The alternative is a steel trough liner which can be cast into the concrete or used to provide a casting mould for high strength concrete. Also available are compact screw pump stations: these are designed to be bolted to the structure, come ready assembled and provide all of the necessary support for the screw pump and the drive unit. Beyond this, the diff erences are quite subtle; the design of the top and bottom bearings, the number of fl ights and the actual dimensions of the screw itself. How much mainte- nance do Archimedes screw pumps require, and how long do they last? Typically, a screw pump can operate for 20-30 years without losing a signifi cant amount of effi ciency, which is governed by the gap between the edge of the fl ight and the trough in which it sits. Modern, sealed- for-life bearings and the use of specialist coatings mean that a screw can be designed for extended durability in a wide range of applications. ECS off ers a full maintenance framework to support existing installations, with screw renova- tions, trough repair and bearing replacement all available The Archimedes Screw is one of the oldest and simplest of pump designs