Archimedes screw pumps boost infrastructure in Mansfield
Archimedes screw pumps may work on a centuries-old design but they are still the most efficient way of lifting water over a short distance. Here, we learn more about their operation at a recent installation at Severn Trent's Mansfield STW
by Jamie Wesley, Contracts Manager, Water Control Division, ECS Engineering Services
When three Archimedes screw pumps at the inlet of Severn Trent Water’s Mansfield Sewage Treatment Works required replacement, NMCNomenca contacted ECS Engineering Services to source and install new pumps. As the exclusive UK service agent for Landustrie Archimedes screw pumps, ECS was able to replace the screws to bolster the water treatment infrastructure at the site.
Mansfield Sewage Treatment Works lies adjacent to the River Maun, processing the majority of effluent water from farms and homes in the surrounding area. The three original screw pumps at the inlet station had been operational since the 1970s, and were displaying a drop in efficiency due to overall wear. As the pumps were beyond refurbishment, the Tier 1 contractor for Severn Trent Water, NMCNomenca, called on the services of ECS to deliver a solution. ECS was selected due to a proven track record, having previously installed similar systems at the Warmsworth and Melton Mowbray.
ECS Engineering Services proposed the installation of three Landustrie screw pumps, each offering a maximum pumping capacity of 800 litres per second. Market leaders in the screw pump industry, Dutch manufacturers Landustrie deliver 100 years of industry experience to its range of pumps. Each of the 14-ton Mansfield screw pumps is expected to last 30 years in operation, providing one of the most efficient methods for moving effluent water over a short distance.
Each pump needed to be replaced individually, in order to ensure the Mansfield works could still service operational demands during the project. The timeframe for replacing each 13.5 metre long pump was around 8 weeks. Initially, the original screw pumps were removed by crane, so that they could be transported off site for recycling. Bearings and drives were then replaced, with the new screw craned into the trough to be installed subsequently.
Next, the hand re-screeding 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 flights, which provides maximum pumping efficiency.
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 offering that is unique to ECS. Our close working relationship with Landustrie ensures a reduced lead time on orders, while our fabrications division has the flexibility to deliver almost any requirement.”
Furthermore, ECS offers 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 efficiency benefits of screw pumps, reducing downtime for operators. No screw pump installation is the same, so this integrated support framework offers operators a one-stop-shop for all their screw pump requirements, no matter the variation in system.
FACTFILE: ARCHIMEDES SCREW PUMPS
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 efficient method of moving water over a short distance.
The basic principle is an inclined tube, fitted with flights 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 lift water up to a height of 12 metres, with a maximum flow 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 advantages of this type of pump over other designs?
The Archimedes screw pump offers 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.
The screw pump offers a very efficient 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 fish 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 fish at the inlet where the blade and trough interfaces meet.
In contrast, a centrifugal pump acts as a permanent barrier to fish 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 different types are available?
The major differentiation between screw pumps is the type of trough in which they are located. The traditional hand screeded trough uses the screw itself to create the exact clearance required for optimum efficiency. 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 differences are quite subtle; the design of the top and bottom bearings, the number of flights and the actual dimensions of the screw itself.
How much maintenance do Archimedes screw pumps require, and how long do they last?
Typically, a screw pump can operate for 20-30 years without losing a significant amount of efficiency, which is governed by the gap between the edge of the flight 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.
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