Your country is not included? Please visit our global website Language Suctioning Liquids: Direct-Liquid Transfer vs. Vacuum-Over-Liquid Transfer Liquids can be drawn using the direct-liquid or the vacuum-over-liquid transfer method. It is important to know the differences when choosing the right approach and pump solution. Drawing liquids seems like a simple task, but choosing the right aspiration method can be difficult. One option is direct-liquid transfer, where media is pumped directly through a liquid pump. When using vacuum-over-liquid transfer, a vacuum is used to suck in the liquid. Both approaches have their advantages, but also limitations. It is important to understand the differences to meet the specific requirements of the application. In cases where the focus is on liquid transfer instead of liquid aspiration, the lesser-known pressure-over-liquid transfer can be an alternative approach. The liquid is transferred from a source container (1) via a liquid pump (2) into the receiving container (3). Direct-Liquid Transfer Explained Using the direct-liquid transfer approach, a pump sucks in the liquid from a source container on the inlet side and discharges it on the outlet side into a receiving container. Through steady operation, this pumping method can create accurate and consistent flow rates. Advantages of Direct-Liquid Transfer Systems Pumps for direct-liquid transfer systems offer a wide range of advantages. However, those advantages are determined by the specific pump technology used. Regardless of the exact pump technology, direct-liquid systems usually offer the following benefits Quick and efficient liquid transfer Continuous liquid discharge Low system complexity Excellent flow rate control Many systems designed with this approach also offer low maintenance requirements. The following advantages can be achieved by selecting the right pump technology High chemical resistance Long-term reliability and long lifespan It is important to know the application-specific requirements to choose the right pump type for this transfer method. Direct-liquid transfer systems that combine all these advantages are ideal for aspiration applications. This includes waste removal in medical and diagnostic applications, inkjet printing systems, and laboratory applications. Limitations of Direct-Liquid Transfer Applications requiring high cleanliness and frequent cleaning of the liquid system might also face problems, because most pumps cannot be cleaned, sterilized, or disinfected easily without leaving residues. The setup of highly complex systems with this approach might also be challenging as one pump is needed per media stream. This makes the design of systems that need to transfer liquids in many different separate lines difficult and potentially costly. Diaphragm Pumps: The Best Choice for Direct-Liquid Aspiration To ensure a perfect fit for the specific requirements of the liquid and application, KNF diaphragm pumps can be customized. This makes them not only highly versatile and chemically compatible in demanding applications but also guarantees a long service life with low maintenance needs. The diaphragm functions as a dynamic seal ensuring leak-proof operation and minimizing the risk of contamination when transferring corrosive, aggressive, or sensitive liquids. KNF Smooth Flow diaphragm liquid pumps such as the FP 70 provide a precise and smooth flow with low pulsation for direct-liquid transfer applications. Some systems require minimal pulsation. While diaphragm pumps are often ideal solutions, they, like all positive displacement pumps, generate pulsation. KNF has developed Smooth Flow technology allowing diaphragm pumps to be used in systems that are sensitive to pulsation. KNF’s Smooth Flow technology uses integrated dampers or several phase-shifted diaphragms to minimize pulsation. The FP 70 Smooth Flow pump is one such example. Working Principle of Vacuum-Over-Liquid Transfer A vacuum pump (1) evacuates air from a receiving container (2) that is connected via lines and valves (3) to source containers (4). The pressure difference allows the liquid to be sucked in. Advantages of Vacuum-Over-Liquid Transfer The vacuum-over-liquid transfer approach offers advantages for many applications. Since the pump has no direct contact with the liquid, it is advantageous for particularly aggressive, hazardous, abrasive or sensitive fluids. This allows the media to maintain purity while preventing contamination and protecting the pump. It is a very versatile transfer method and can be used for a wide range of media, especially ones that have a high viscosity or contain particles or fibers. This transfer method also allows the setup of complex systems with just one pump powering multiple media streams. Limitations of Vacuum-Over-Liquid Transfer Vacuum-over-liquid systems also face challenges caused by the physical nature of liquids in the vacuum itself. The boiling point of liquids decreases as the vacuum becomes stronger. If the required transfer conditions – boiling point of the liquid, required vacuum level, and temperature – cause the liquid to boil, it cannot be transferred using vacuum. The vacuum effectiveness can also decrease with distance because of pressure losses in the system, which limits the maximum distance over which the liquid can be drawn. Vacuum-Over-Liquid Transfer With Diaphragm Vacuum Pumps The air evacuated in vacuum-over-liquid setups is in direct contact with the liquid and therefore normally contains moisture. This is important when it comes to transferring wet gases or aerosols, as condensate may form in the pump which can damage it. It is therefore important to design the pump specifically for handling condensate. To achieve this, KNF uses a highly modular system, which turns its diaphragm vacuum pumps into highly modular solutions designed to fulfill the specific needs of different customer applications. In addition, the pump should be installed as high up in the system as possible so that condensate can drain out. The diaphragm gas pump N 838.1.2 from KNF can be used for the vacuum-over-liquid transfer and ensures an outstanding performance-to-size ratio. Diaphragm gas pumps like the N 838.1.2 from KNF combine these benefits and offer a high-performance level combined with a compact size. Which Transfer Method Fits Best – Direct-Liquid or Vacuum-Over-Liquid Transfer? Choosing the ideal transfer method along with the right pump solution depends on the specific application requirements. The experts at KNF help customers choose the right approach and customize diaphragm pumps for each approach to their exact needs. Get in touch with your KNF expert to find the right diaphragm pump for your application. Contact Us Do you want to find out more about our customized pump solutions and service opportunities? Get in touch with our local sales representatives.