ECS Engineering Services has recently commenced works as part of the latest phase of Scottish Water’s £250m city-wide programme to improve sewage management in the Glasgow area. Over the next eight months ECS, in association with Landustrie, will be installing and commissioning 14 new screw pumps at the Shieldhall water treatment works, which serves most of the centre of the city.
Shieldhall is the largest of the Glasgow area’s waste water treatment works and serves a population of about 600,000 in the south of Glasgow, Newton Mearns and Renfrew areas.
The Shieldhall site has been modernised several times over the years to meet the growing demand of an ever-expanding population in Scotland’s largest city. As part of the current programme it was realised that the 14 large Archimedes screw pumps that drive the process were getting towards the end of their service lives and needed replacing.
There are four low level and six high level screw pumps, each weighing 13 tonnes, being 16m long and 2.4m in diameter and capable of pumping 960 litres/sec. There are also four larger RAS (return activated sludge) pumps, each 16m by 2.6m with a flow capacity of 1580 litres/sec.
The recent contract award was to provide like-for-like pump replacements, but ECS realised that this would have meant service engineers working in the original concrete troughs, hand screeding the screw pumps for several weeks to create the formed pumping troughs. This process exposes the engineers to unnecessary risks, so in conjunction with Landustrie in the Netherlands the design team looked closely at the design of the equipment to eliminate as much of this as possible, whilst ensuring the client still received the best standard of equipment currently available on the market.
In conjunction with ESD, Scottish Water’s supply partner, several design upgrades were made, the most significant being the alleviation of the requirement to hand screed the new machines into the concrete trough. The pumps were assembled in the factory complete with the new steel coated troughs, these can be moved into position relatively easily, without the fitters having to work in confined and potentially dangerous spaces. Upon successful installation of the new pump and troughs the whole machine will be backfilled with concrete giving both strength and durability far better than the original installations for many years to come. This design upgrade was a major health and safety gain that both Scottish Water, its main contractor ESD and ECS were keen to embrace.
Scottish Water specifications stated that a v-belt drive system should be used, with a direct-on-line drive configuration. This simple but efficient arrangement is appropriate because the slowly rotating pumps run continuously so there are no regular start-up impulses or shock loadings. To compliment this further, ECS has installed new high efficiency motors, which over the course of their long working life will save a considerable amount of energy.
ECS has also delivered further long-term savings thanks to the installation of Landustrie stainless steel ECO, sealed-for-life bottom bearings that are maintenance free for the lifetime of the bearing. Together, the complete installation will provide long-term reliability and efficiency for the treatment works for many years to come.
New pump bearings save €28,970 per annum at energy plant
Faced with frequent failures on its centrifugal pumps for water recirculation, a large CHP (combined heat and power) plant in Romania asked NSK and its local distributor to perform an on-site pump bearings investigation. The outcome identified poor lubrication of the pump bearings as the source of the failures, with NSK recommending the adoption of sealed-for-life bearings featuring DDU seals and high-temperature grease. In total, the move has led to annual cost savings of €28,970, while simultaneously offering a significant improvement in performance.
Dreamstime Prior to switching to the NSK solution, the CHP plant was suffering bearing failures on its centrifugal pumps every three months. Analysis by NSK showed that oil was leaking from the bearings as a result of poor seal condition. With 30 pumps on site, the facility was spending a significant amount on replacement bearings, oil replenishment and maintenance. When adding the cost of downtime, it became clear that a new strategy was required.
The CHP plant asked NSK´s local distributor to assess the potential for improving the lifetime of the bearings. Considering the age of the equipment and the poor condition of the seals, a design modification to avoid the oil leaks was not considered. Instead, a trial using NSK DDU Sealed Deep Groove Ball Bearings filled with high-temperature grease was performed on three pumps. With no failures occurring after six months of operation, the decision was taken to adopt the NSK solution on all pumps. Following 12 months in service, zero failures have been recorded.
NSK´s DDU Sealed Deep Groove Ball Bearings feature high-quality, ultra-clean steel that is known to extend bearing life by up to 80%. Super-finished raceways are specially honed to minimise noise and improve lubricant distribution and life, while patented seals provide resistance to contamination in the toughest environments. Another advantage of this type of bearing is the pressed steel cage, where close-coined cage pockets and tightly controlled clearances reduce friction and ensure even distribution of the lubricant. The grease offers high temperature resistance and speed capability, with good resistance to water and contamination.
Ultimately, it is the elimination of downtime, maintenance and oil replenishment costs, as well as lower bearing costs, which have led to the calculated annual cost savings at the CHP plant.
Mark Water Pumps leads the way on the aftermarket
While virtually all automotive components are modelled using CAD, computer testing can only take you so far. To really gauge how suitable a component is for a vehicle, physical endurance testing is the only sure-fire way to prove a component or assembly can function properly in the real world. This is why businesses such as Mark Water Pumps Limited (MWPL) operate in-house automotive testing facilities, offering the aftermarket industry an opportunity to independently prove component performance.
MWPL has invested in its Automotive Testing Centre in Colwyn Bay, Wales, to help prove the performance of external products, as well as its own range of OEM equivalent PROFLOW water pumps. The dedicated testing centre has the capability to test water pumps, expansion tanks, thermostats, cooling systems, clutches, clutch bearings, brakes, oil pumps, timing belts, wheel bearings and belt tensioners as well as a host of associated components. Endurance and destruction testing is equally available, ensuring that customers have the means to prove quality, operational suitability and performance of products.
Such a breadth of testing facilities can be invaluable when introducing a new product to the aftermarket. While a product or component may pass computer simulations, nobody really knows how a component will perform until it is subjected to real-world operating conditions. It’s a vital part of product development, ensuring that when a new component is released to market, the risk of recalls or premature component failure is effectively minimised.
Conversely, physical testing is another important part of failure analysis. Being able to accurately replicate failure conditions for a component can provide manufacturers with greater data when carrying out fault analysis. Again, it can serve to identify design or operational limitations to allow further development of the component or product in question.
Either way, a customer can gain from greater quality assurance, as David Lewis, Plant Manager at MWPL explains: “When you buy an OEM component, you can be sure that the manufacturer has carried out physical endurance testing before it was released to market as part of the original vehicle. However, in the aftermarket this is not always the case, as manufacturing and testing standards can vary. In this case, importers and distributors can also ensure the replacement component they are buying meets the standard of components they are expecting”
“Utilising independent testing facilities such as the Mark Automotive Testing Centre means you can get this all-important assurance. It should be at the forefront of product development activity for aftermarket manufacturers and distributors, and this is something consumers in the aftermarket should be looking out for.”
Key questions for selecting a wastewater solids handling pump
If the liquid you’re pumping contains solids, there are a number of solids handling submersible pumps that might be appropriate for your application. To avoid clogs or burning your motor out, you need to make sure you have the right pump. There are key questions that help determine which pump will solve your problems. In this post, we’ll examine these questions so that you’re prepared when you talk with your provider.
What type of solids are you’re pumping?
Understanding the solids in your liquid helps your provider determine the right type of pump for your application. We’re focusing on wastewater, so we can assume your solids are not abrasive (abrasive solids would require a hard metal, agitator pump). Most likely, they are large and soft or long and stringy. You also need to know if the solids need to be reduced to go into your system or to discharge, or if you just need to pass them.
Large and soft solids generally need a shredder pump that will shear the materials before pumping. Long, stringy solids indicate that you’ll need a vortex pump that can pass the entire solid.
Understanding the type of wastewater is also helpful. These are generally categorized as municipal (including sewage) or industrial. While municipal wastewater is generally consistent among sites, industrial wastewater solids and contaminants often vary based on industry.
What solids loading can the pump handle?
There needs to be enough liquid either in the sump or in the system to keep solids moving with the liquid. Without enough water, the pump will clog and won’t be able to pass the solids. Most solids handling pump designs can handle approximately 5% solids by volume. If your wastewater has a higher concentration, you will likely need to add more water to the sump by changing the system to allow more water to accumulate in the sump or by adding more water to the process.
The sump pump basin size is also a factor. The basin should be sized to minimize the number of cycles per hour but cannot be so large that solids will settle instead of being brought into the pump.
How might your piping system affect the pump you need?
Understanding the design of your piping system will help your provider make sure there are no areas where the solids may settle, build up and cause clogs. This includes:
- Size of the Piping: It must be large enough to pass solids downstream, but small enough to maintain carrying velocity to prevent solids from settling out. We recommend carrying velocity of 5-7 ft./sec. for municipal wastewater applications. As the specific gravity of the solids increases, you may need to further increase the velocity to carry the solids.
- Vertical Lift: This is the height that water has to travel as it moves through your piping system. A significant vertical lift combined with an improperly sized pump can cause solids to recirculate and clog within the pump volute.
- Location of Check Valves: The check valves should be as close to the pump as possible. If too far from the pump or too high, solids can build up before reaching the valve. This causes clogging as the solids backflush into the pump. Adjusting the location of the check valve generally solves these issues.
In some instances, your provider may conduct an inspection. If the entire piping system isn’t visible, you may need to show the piping system plans or explain where and how far the piping goes. The piping connections and fittings are important too.
What is the required flow rate for your system?
The flow rate is the amount of liquid that runs through the system in a given amount of time. This and the pipe sizing determine the velocity needed to pass the solids downstream through the pipes. The flow rate also indicates the appropriate size your sump should be. An undersized sump causes the pump to cycle too frequently and burn itself up.
If you don’t know your flow rate, here are two options to help your pump provider determine it:
- Calculate the flow rate by performing a draw down test. With no water entering the sump, allow the current pump to run for as long as possible while recording the time in operation. The flow rate is the volume of liquid pumped (sump length x sump width x the change in liquid level from start to end of pumping cycle) divided by the amount of time recorded during the drawdown test.
- If you have the model number of your current pump, researching the pump’s performance curve combined with the piping system information or a pressure gauge reading in the system can help your provider calculate the flow rate.
Translating answers to the solids handling pump you need
The answers to these questions provides the information your provider needs to make a recommendation. The natures of the wastewater and solids determine the type of pump you need (i.e. shredder or vortex pump). The flow rate (and the amount of head in the system) indicates the specific pump model you need.
In addition, you may have unique circumstances to consider, especially when dealing with harsh environments. These are the types of situations in which BJM Pumps excels. We build submersible pumps to deal with rugged applications and have 35 years of experience helping customers dealing with the issues you deal with every day. Contact us or call us at 860-399-5937 to request more information or to initiate a personalized evaluation of your submersible pump needs.
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