The amount of water a pump can move in a minute is called its flow rate. This is measured in liters per minute or LPM.
In this paper, we present a pump-less forward osmosis (FO) and low-pressure membrane (LPM) hybrid process. This system reduces energy consumption by using the inner pressure of the DS tank to operate the LPM process.
Pumps
A pump uses a motor to convert electrical or hydraulic energy into rotational mechanical energy. This energy is used to rotate the shaft of the pump, which in turn rotates the impeller and produces flow and pressure.
Pumps rate their flow in gallons per minute, or GPM. Unlike pressure, which measures resistance to flow, GPM measures the amount of liquid moved over a set period from the tank or reservoir to the outlet. A motor can produce a large amount of GPM, but if there is no head (see below), the pump will not be able to create its advertised pressure.
When fluid enters the pump volute (casing), it loses some of its kinetic energy through friction with the interior surfaces of the casing and is converted to pressure energy. The pumped fluid also generates a head in the process of piping through friction and other losses. A pump is rated to create a certain amount of pressure at a given speed, and this is typically measured in PSI or pounds per square inch.
A pump needs to be operating at, or close to, its best efficiency point (BEP) in order to achieve the most efficient performance. The BEP is usually stated in the pump curve or manual and may be obtained by consulting with the pump manufacturer.
Flow Rate
The amount of water (in liters per minute) that a pump can pump is the pump’s flow rate. Flow rates are typically based on the head pressure, shaft speed, and impeller diameter. This information can be found on the pump performance curve.
In addition, the pump’s horsepower needs to be considered. Choosing the correct horsepower is essential because it can affect the maximum and rated flow rate of the pump as well as the suction and discharge head of the pump. Generally speaking, the horsepower required to maintain a specific flow rate increases with increasing shaft speed. This is because the fluid’s viscosity increases with shaft speed.
A common mistake made by many pump operators is to select a pump based on its PSI rating rather than on its flow rate. This can result in a pump that cannot meet the application’s needs for head and flow operating points, even when the pump is rated at a particular head.
Other variables, such as piping and water-saving heads and aerators, also influence flow rates. This is why it’s essential to consult a pump expert to ensure that you have the proper equipment for your needs. To do so, contact the pump experts at Sanitary Fittings to help you read pump performance charts and select the best pumps for your application.
Head
One of the most misunderstood physical characteristics of pumps is the head. Many people don’t understand what it is, how it relates to pressure, or why it’s crucial. This article will demystify the concept of the head so that you can understand how a pump works and select the right pump for your application.
The head is the height at which a pump can raise a liquid. It is equal to the vertical distance from the suction tank level to the pump centerline + the height of the discharge point of the pump plus a quantity to account for the losses in the pipe. The head is usually measured with manometers on the pump suction and delivery lines. The head is also sometimes confused with pressure during pump selection. While both measure pressure, the latter is fluid-dependent and varies with the density g of the working fluid.
A pump manufacturer can only tell you how much head a pump can produce if they know the type of water that will be available in the suction tank. Since they do not know what the water supply will be, most manufacturers solve this problem by subtracting the head open at the suction from the discharge to get the pump’s head. This head is then expressed in feet of head on the pump’s performance curve.
Displacement
The displacement is the volume of liquid that a pump moves in one cycle. The higher the displacement, the more energy it requires to operate. The fluid’s viscosity also influences the displacement. Choosing the right size pump for your application can help you save money on electricity costs. A pump that is too small won’t be able to keep up with your system demands, while a pump that is too large will waste power and create unneeded noise.
The FO-LPM hybrid process is a new energy-saving water treatment method that does not require a pump for regeneration of the draw solution (DS). The FO process provides an osmotic pressure difference that drives permeate across the membrane. The DS tank’s inner pressure generates the LPM process, which re-concentrates a diluted DS to maintain its concentration and produce clean water.
Using a loose membrane for the LPM portion of the hybrid FO-LPM process allows it to be operated at a lower pressure than relatively tight membranes. This allows the LPM process to be used for a more extended period, which increases DS permeate volume and improves filtration performance. The optimal PSS concentration for this system was determined based on the results of the individual FO and LPM processes. FO-LPM was successfully demonstrated as a viable energy-saving water treatment technique.
