Vanes made of the bearing polymer Hitemp 150 have lasted three times as long as traditional vanes in servicing company Septic Tanks (Pty) Ltd’s vacuum rotary pump, a Broom B35.
The pump is used to create a pressure difference that sucks up the waste liquids from septic tanks.
The pumps involved in such operations should not come into contact with sewage ideally.
However, where septic tank pumping is not monitored continuously, overflow from the transport truck can make its way to the pressure vessel and on to the vacuum rotary pump.
The vanes in these pumps thus need to be cleaned.
In addition, the vanes need to be able to operate at high temperatures, since the pumps can overheat due to operation for long periods.
Armed with information about vane operating requirements, when the original laminate vanes in Septic Tanks (Pty) Ltd’s Broom B35 pump needed replacing as frequently as every 6 months, the waste-sector servicing company turned to Vesconite Bearings, the maker of various polymers, for a solution to this unique operating environment.
Vesconite Bearings technical sales consultant Phillip de Villiers recommended Hitemp 150, an engineered polymer that is wear resistant and can withstand temperatures of up to 150ºC.
This material will not delaminate as does the original-equipment-manufacturer supplied material, a thermosetting phenol formaldehyde resin that impregnates layers of cotton to produce a hard synthetic plastic, he reasoned.
The trial result has been impressive: Hitemp 150 did not delaminate unlike its competitor and it was resistant to overheating.
In addition, the new polymer vanes coped well with the frequent pump cleans that were required when waste material accidentally entered the pump.
Septic Tanks (Pty) Ltd owner Charl Neuhof is also pleased that the Hitemp 150 vanes continue to operate after a year and a half, while the phenolic alternative had to be replaced after six months.
Moreover, he is enthusiastic about the reduced maintenance costs that are associated with the product, which can be cleaned in-situ unlike the previous variety of vanes that had to be removed prior to cleaning because of their high levels of swelling when exposed to water.
Since testing of the B35 vacuum rotary pump vanes has gone well, Neuhoff plans to replace the vanes on its fleet of truck pumps as they fail.
His four trucks are used in the Johannesburg North, Pretoria, Hartebeespoort and Brits areas of South Africa, with three out on the road daily, each carrying six 6000 litre loads of waste material a day.
The five vanes that were employed in the B35 pump measured 35mm by 6mm by 330mm and had chamfered edges, but vanes for the other pump models that will be introducing the Hitemp 150 vanes will have different dimensions.
Glasgow’s new screw pumps secure long-term sewage treatment
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.
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.
Giant screw pump to be replaced
ECS Engineering Services is to install a replacement screw pump at Wessex Water’s Avonmouth Sewage Treatment Works (STW), helping secure the capabilities of the facility for decades to come.
Avonmouth STW serves a population of about 1,000,000 people in Bristol and the surrounding towns and villages. One of its key pieces of process plant is a very large screw pump which has been in operation for around 40 years. However, it had become badly worn and effectively reached the end of its useful service life.
ECS was asked to inspect the screw pump and make some proposals for its overhaul or replacement. Jake Laughton, the ECS engineer who led the inspection says: “Much of the pump is in a serviceable condition and can be retained, however, the screw itself has reached the end of its life and needs to be replaced.”
At 21 tonnes, 20 metres long, 3.1 metres in diameter and able to pump 3,645 litres of water a second, the screw is simply enormous. ECS has arranged to have a new screw fabricated in Holland by long-standing partner company, Landustrie. Made in mild steel, a high-performance, corrosion resistant coating will give it a working life measured in decades.
“We have incorporated some important innovations,” says Jake, “including a stainless steel lower bearing, again made by Landustrie. This does not need an oil or grease feed, so is both ecologically sound and reduces the maintenance requirements – features that will pay dividends in the long run.”
The design team has evaluated the loading on the pump when it is in use and optimised all the new parts to lengthen the pump’s working life and maximise its efficiency and reliability.
Jamie Wesley, Operations Director at ECS states, “To be involved with machines of this size showcases the excellent capabilities available here at ECS, our screw pump experts have given the existing motor, gearbox and upper bearing a clean bill of health, which has helped to reduce the overall cost of the project for Wessex Water.”
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