On the other hand, the highpressure series keeps a steady rate of climb as the feet of head peaks. The high flow challenger on the right shows a sharp dip as the feet of head pressure rises. Volumetric flow rate v, on the horizontal axis, is the rate at which fluid is flowing through the pump. Pump sizing involves matching the flow and pressure rating of a pump with the flowrate and pressure required for the process. The gpm is affected by how high the water needs to be pumped the head. Pump performance curve a centrifugal pump performance curve is a tool that shows how a pump will perform in terms of head and flow.
The pump speed is changed when the impeller size is constant. Pump selection, sizing and interpretation of performance curves 4 7 practice to plot the system curve for higher flow rates than the design flow rate, since flow demand may change and extra capacity may be required. Find the products flow rate 75 gpm on the flow rate vs. A comparative study on centrifugal pump designs and two. Pump efficiency is the best combination of head and flow at the least energy consumption. Using the doubled rate, the 400 gpm flow rate with its corresponding 8. Once the flow rate q is defined and the delivery head h is calculated, the operating point of the plant can be determined. The head pressure against which a submersible pump operates is referred to as total dynamic. It is recommended to select a flow that is higher than the minimum to account for decrease in flow that naturally occurs as the filter becomes loaded with dirt and debris. In this example, if pumping against a head of 40 ft using an impeller size of 7. This can be applied to pumps within hvac industry such as chilled water pumps. For a given pump speed, as defined on the xaxis, each flow rate pump head data point can be derived by identifying the point where each pressure line crosses the xaxis for the selected pump speed. Determine the flow rate and developed head for the pump used. The relationship between the capacity or flow rate versus travel follows a specific curve.
What is total head 10 what is the relationship between head and total head 11. Conversely, if the pump is located above the water to be pumped, then the suction head is positive and the pump head will decrease. This is because the pump must use energy to bring the water to the level of the pump. Volume flow rate q, also referred to as capacity, is the volume of liquid that travels through the pump in a given time measured in gallons per minute or gpm. Pumps can generate high volume flow rates when pumping against lowpressure head or low volume flow rates when pumping against highpressure head. Relationship between pressure drop and flow rate in a. As a matter of fact there is a strict relation between them which is defined by the fluid specific gravity, so the relation is fluid dependent. The plot of head versus flow rate is known as the pumps performance curve see figure 7 for an example of a pump performance curve. If you have to pump a liquid up 30 feet and your pump doesnt have at least 30 feet of head, then there is no chance it will work.
At this flow rate the pump produces exactly what the system piping requires. Friction head loss the resistance to water flow, as expressed. Performance flow at the maximum pump head, the flow of a water pump system is zero. Pump sizing pump sizing involves matching the flow and pressure. Capacity the rate of liquid flow that can be carried. To size and select a centrifugal pump, first determine the flow rate. Flow rate and flow head can be influenced via the control fittings installed in the delivery pipe. With an increase in pump flow rate, the head developed by the pump start decreases. Most pump applications involve moving fluid to a higher level. That zone is where the pump operates most efficiently.
Engineers have a common language and analytical models to describe pump performance. They provide lift which overcomes head pressure, which is measured in feet. Flow is indicated on the xaxis while pressurehead is indicated on the yaxis. Total head for a given flow rate will have determined the impeller diameter to select according to the performance curve. Head a measure of the pressure or force exerted by the fluid. Improve flow rate by understanding control valves pumps. Sometimes head can be confused with pressure during pump choice. The pump develop maximum head at zero flow it is called shutoff point or shutoff head and the corresponding pressure is called shutoff pressure. A pump has been selected f rom manufacturers details that can achieve the required flow at the bwl at a speed of 675 rpm. In order to optimize the pump design, the flow rate must be accurately determined. If you are a home owner, find out which of your uses for water is the biggest consumer. Head vs flow curve hq in this curve, the head is on the vertical axis and flow rate on the horizontal axis. Head loss does not reduce the fluid velocity consider a constant diameter pipe with a constant mass flow rate, and it will not be effect the elevation head of the fluid consider a horizontal pipe with no elevation change from inlet to outlet. The steps to follow to select a centrifugal pump are.
Pump design equations formulas calculator discharge flow rate. As shown in the sample performance curves, usually 3 curves of differential head vs. The total head is the effective mechanical energy transferred by a pump to the fluid as a. Axialflow pumps lower pressures and higher flow rates than radialflow pumps. Typical selection criteria for centrifugal pumps are their design data flow rate or capac ity q, discharge head h, speed of rotation n and npsh, the. Pumps and pumping system bureau of energy efficiency 115 figure 6.
The objectives in this example are to accomplish the following. Swpa handbook and the hydraulic institute for the above terms. Hence, there is a certain flow at which both the system and pump head curves match. Note thatqis also used as the symbol for heat transfer. These curves define the envelope of the pumping system.
This is the primary information reported in the pump performance curves and very important information regarding most of the pump calculations related to differential pressure across the pump. The pump selection of a pump is driven by the following main parameters. The flow rate is the effective volume flowing per unit of time through the discharge connection of a pump. Pipe flow expert modelling positive displacement pumps. In practice, to get the optimal system you have to select the pump capacity i. This curve can be used with a shear rate curve for the tubing that is used in the system, to determine the apparent viscosity.
Usually the operating point is not on the qh curve of the pump. The system curve c describes the relationship of pressure drop and flow rate for the given piping system with no static head. Pdf dimensionless characteristics of centrifugal pump. Topics covered include total dynamic head, lift, loss, flow, pressure, friction loss head loss, and converting psi to feet. The maximum total head developed by the pump is at zero capacity. Flow friction head sometimes called dynamic head loss is the friction loss, on the liquid being moved, in pipes, valves and equipment in the system. The centrifugal pump head, on the other hand, decreases as the flow increases. The total head is the effective mechanical energy transferred by a pump to the fluid as a function of the weight force of the fluid.
Manual for the design of pipe systems and pumps gea group. The possible combinations of total pressure and volume flow rate for. In practice the combined head and volume flow moves along the system curve as indicated from 1 to 3. Using the doubling flow rate rule, the 200 gpm flow rate with its head loss of 2. Solution first determine the head flow characteristic for the system. The pump curves show a comparison of flow rates in congruence with horsepower and feet of head. For a centrifugal pump what is the relation ship between. Flow rate q 4 head h metres 4 performance range 60 hz n 3450 rpm nomenclature singlephase motor flow rate us g.
Alhough certain system head parameters are calculated the same way whether the driving force for flow is a pump or gravity, this article mainly addresses sizing concerns for rotodynamic pumps. The most common shape of a total head against capacity curve for a conventional volute centrifugal pump is shown in figure 4. In a system where there is flow, the total head is the difference between the discharge head and the suction head plus the friction head and this sum will be less than the shutoff head. Make sure the aquifer is capable of supporting your desired flow rate. Therefore, head loss will always act to reduce the pressure head, or static pressure, of the fluid. Flow rate depends on elevation difference or static head 7. Crescent is attached to pump head crescent is stationary and separates the rotor and idler teeth, providing the.
The initial flow is 100 gpm, the initial head is 100 ft, the initial power is 5 bhp, the initial speed is 1750 rpm and the final speed 3500 rpm. This is the first video in our new series on buying a pump and the. The geometries of the two pumps are designed for the same flow rate and shut off head coefficient with the same impeller rotational speed. The system head increases as the flow rate increases. Pd flow rate is relatively independent of viscosity. In any one application these parameters may be more or less important. Depending on the required delivery head, the centrifugal pump will find its operating point when the plant curve and pump curve meet. Pump flow is taken at the largest impeller diameter for double suction impellers pump flow is divided by two ns specific speed n pump speed, rpm q flow, m3h h head, m values are taken at best efficiency point bep pump flow is taken at the largest impeller diameter for double suction impellers pump flow is divided by two. Examples of total head calculations sizing a pump for a home owner application. Centrifugal pumps in parallel are used to overcome larger volume flows than one pump can handle alone. Head pump head and shutoff head pressure explained.
Because pressure drop varies with the square of flow rate, the equation of the system curve can be estimated by fitting a quadratic equation through the origin and the design operating point. Typical centrifugal pumps will show an increased flow rate as head pressure decreases. Centrifugal pumps are characterized by the relationship between the flow rate q they produce and the. When reading these curves while choosing a pump, there is a certain optimum zone on the pumpcurve graph that you want to stay in. Changing the travel of a control valve will change flow rate. Power input the electrical input to the motor expressed in kilowatts kw. When we talk about how much water a pump will move, the volume, we will refer to the max flow rate as measured in gallons per minute gpm. The flow rate between the minimum flow based on the turnover rate and the maximum flow based on water velocity.