These FAQs are designed to be helpful in providing information and increasing awareness of Flygt's application know-how, technological capabilities, and engineering expertise.
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How is a pressure sewer system different than a gravity system?With a gravity system, discharge lines are laid on a grade to pumping stations or large diameter trunk sewer mains. Minimum pipeline grades must be achieved to ensure that the wastewater velocities are sufficient so that solids don't settle and odors don't occur. This requires deep excavations and is therefore not economically viable where terrain becomes difficult. On the contrary PSS systems utilize small diameter discharge lines that follow the contour of the terrain at a shallow depth.
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How can I verify that the station has a good hydraulic design?By using the experience from equal or similar stations that are well functioning. By following design standards such as the Hydraulic Institute's intake design standard (14.6) and consulting Flygt pump station design guides. Physical model tests or Computational Fluid Dynamics (CFD) analysis may be needed for designs that depart from the above. What can Computational Fluid Dynamics (CFD) anlaysis be used for?Using CFD, we can build a computational model that represents a system or a device that we want to study. We can model complete pumps with rotating impellers or more complex systems such as pump stations, mixing or aeration tanks, both for new design and for troubleshooting existing stations. Experienced CFD experts using high end software can fine tune hydraulic designs for optimum performance at a lower cost than performing a physical model. Engineers and end-users will know that the resulting design will function well. What adverse hydraulic phenomena can appear in a pump station?Surface and subsurface vortices, entrained air, uneven velocity distribution at the pump intake and excessive pre-swirl, velocity variation over time. These phenomena can cause noise, vibration, motor overload, shorten pump life, cavitation etc., and must be avoided in the station through correct station design.
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Why is it important to perform water hammer analysis?To predict if water hammer will occur in the system and so as to recommend installation of the cost-effective protection devices. Water hammer is a type of hydraulic transient occuring at pump shut down. It leads to rapid changes in pressure in the discharge piping, which can have devastating consequences, such as pipe rupture. Why is it important to perform start caclulations?To assure that the selected pump operating in the intended system will start correctly, avoid unecessary loading on the supply network and control the peak starting current. Start calculations can be used to optimize hydraulic performance and ensure sufficient starting torque and motor torque, ensuring reliable starts and long-lasting motor and pump station components.
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What is NPSH?NPSH stands for Net Positive Suction Head. NPSH required (NPSHr) is the minimum required pressure at the inlet of the impeller to prevent cavitation. NPSH available (NPSHa) is the available pressure at the impeller inlet. NPSHa must always be greater than NPSHr. Good design practice calls for adding a suitable margin to the pump's NPSHr in order to assure smooth pump operation under different operating conditions. What is cavitation?Cavitation occurs when there is insufficient NPSH; i.e. too low a suction pressure induces cavitation. This causes the erosion of the hydraulic surfaces due to the vapor bubbles collapsing. Pump performance will degrade as cavitation is increasing. Additional consequences can be excessive noise and vibration. Suction pressure, liquid temperature, and pump station altitude all effect the NPSH available. What kinds of clogging can occur?Full clogging has occured when the pump is completely blocked by debris. Partial clogging is more common and harder to detect. Partial clogging occurs when solids have collected on parts of the pump hydraulics. This leads to reduced flow and sometimes increased power usage. The solids typically contained in wastewater liquids can be divided into organic, inorganic, abrasive, and stringy. Organic wastewater solids are fundamentally soft and often consist of fibrous and stringy material in smaller and larger accumulations. Inorganic solids are hard, often sharp, and of smaller particles. Long and fibrousm material most often causes partial or full clogging.
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When should I use Hard-IronTM impellers/insert ring?Hard-IronTM impellers have a 25% chromium content, which gives high wear resistance as well as high resistance against erosion corrosion, making it suitable for installations with high content of grit and sand content, as well as when erosion corrosion is expected. Hard-IronTM is recommended for water with a high oxygen content, wastewater with increased chloride content, and applications with abrasive particle content. What is N-technology?The self-cleaning, clog-free N-Pumps have been engineered to give you efficient, reliable, and trouble-free pumping over long duty periods. The secret behind the award-winning N-technology is the combination of a swept-back leading edge and a relief groove in the volute. The innovative and patented hydraulic design of Flygt N-pumps delivers sustained efficiency, which results in reduced unplanned service calls and minimum energy costs. This contributes to a lower total cost of ownership– and total peace of mind.
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What is sustained efficiency?Sustained efficiency is defined as the ability to deliver clean water pump efficiency over time when a pump is operating in its intended application. Many wastewater pump designs will accumulate solids in continous operation, thus leading to lower pump efficiencies. In extreme cases, a pump may become completely clogged. Intermittent on-off operation tends to minimize the performance drop. Modern, self-cleaning hydraulic designs have the best likelihood of achieving sustained efficiency. For pumps operated at long duty cycles, such as VFD operated pumps, it's critical to select pumps that deliver sustained efficiency.
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What is a grinder pump?A submersible pump incorporating a grinding mechanism designed to reduce sewage particulate and pump the resulting mix, often from a residential/commercial building to a wastewater collection system. When should a chopper pump be used?Chopper pumps are recommended in very tough applications including agriculture, food processing, and pump stations in public and institutional facilities like train stations, hospitals, prisons, and hotels; i.e. places where all kinds of things get flushed down the toilets-both fibrous and solid. Equipped with a special impeller and cutting plate, chopper pumps will cut up a wide variety of materials and solid objects into small pieces, that will neither block up the pump, nor the piping.
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What can be monitored on my pump? The following parameters can be monitored by standard and optional sensors: temperature, leakage, vibration, currents, running time, and number of starts. What is monitored by the MAS system?The MAS system is a flexible and user-friendly monitoring and status system that can be configured to accept multiple sensor inputs. Typically, motor temperature, seal leakage, junction box leakage and vibration are monitored. All large pumps and most mid-range pumps benefit from MAS functionality.
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