There are many advantages of flexible impeller pumps in handling viscous fluids over centrifugal pumps. Martin Ruse of Jabsco, a pioneer in flexible impeller technology, discusses the fundamentals of flexible vane pump operation and its many advantages in terms of installation, maintenance and use. Positive displacement pumps such as flexible vane pumps are used as a replacement for centrifugal pumps in many industrial applications. The flexible impeller pump was invented by Jabsco Corporation (now part of the ITT Industries Group for Momentum and Flow Control) about 60 years ago and has the obvious advantage of handling viscous fluids compared to centrifugal pumps. After the impeller turns the eccentric cam, the volume of the cavity per unit decreases. As the cell volume increases through the inlet tube, a partial vacuum is created and the atmosphere forces the fluid into the cavity. As the volume decreases through the outlet tube, the fluid is forced out of the cavity into the outlet tube. The key to flexible viscometer delivery of viscous fluids is that the flow rate is proportional to pump speed. There are two important things to consider here. The first is the friction loss inside the pump itself and the second is the frictional loss between the fluid and the pump inlet wall. Loss of pump friction increases fluid viscosity and results in a drastic drop in centrifugal pump performance. Although viscous friction can be reduced by reducing pump speed, decreasing centrifugal speed can result in a drastic reduction in pump performance, as centrifugal pump performance relies primarily on the speed at which the fluid passes through the impeller. Practical applications of fluid viscosity are limited up to 200-300 cP. The flexible impeller pump can reduce the internal friction loss caused by the viscosity by reducing the pump speed. The pump impeller blades can automatically adjust to speed, fluid viscosity and different pressures. How to get fluid into the pump is a major issue when transporting fluids. The pressure drop caused by the friction loss inside the inlet pipe is an important factor that prevents the fluid from entering the pump. To reduce friction losses, the size of the inlet pipe must increase with increasing viscosity. In addition, the inlet pipe should be as short as possible and not be bent. The harder the fluid is, the more difficult it is for the pump to lift the fluid. If the viscosity is too high, a supply tank with an overflow hopper should be installed above the pump position to provide a positive pressure head for the fluid. The Advantages of Installation The main advantage of a flexible impeller pump is that it can be installed in the most convenient locations for some special applications. Unlike centrifugal pumps, they do not have to be limited to the overflow side when installed below the liquid level. They can therefore be installed in a safe place above the ground, thus avoiding the possibility of the pump or pipe being tripped or damaged by the vehicle. Another advantage is the reservoir configuration, which may not have a matching bottom outlet flange or valve if the reservoir (typically a barrel and can) is provided by an outside supplier. Some containers, such as rubber-lined reservoirs, can not open at the bottom; flexible pump can solve this problem by using a simple hose connection at the top of the reservoir. This tank can be installed either on the ground can also be installed under the ground, and do not set overflow inlet.