general pumping fundamentals

It should in fact be slightly more than 15 feet because a higher suction lift will be required due to friction. Head is defined as energy divided by the weight of the object displaced. If not, there may be something wrong with the pump. Cavitation causes damage. In this case, the distance is 30 feet.

a system. The difference between the two is the total head of the pump. If the velocity is less, then the friction loss will be less and if the velocity is higher the loss will Learn how performance and deviation from control limits can be visualized to allow operators and engineers to understand parameters affecting reliability.

116 0 obj <> endobj Engineers describe pumps based on the kind of motion they use: displacement; mechanism, cylinders, and pressure. You can find the friction loss for a 0.75 pipe at 10 gpm in the Cameron Hydraulic data book of which the next figure is an extract: The total friction loss for piping in the system is then 9 + 3.1 = 12.1 feet. There are numerous reference charts on submergence to use when looking at the suction side design. The horsepower required to achieve a given output depends on the energy source, because different types of prime movers vary in their pumping performance capabilities. If you lift 100 pounds (445 Newtons) up In reality, fluid friction and the negative consequences of vapor pressure will work against you and preclude fluid lifts of much more than 26 feet. Friction head is the amount of energy loss due to friction of the fluid moving through pipes and fittings. %PDF-1.5 % The weight of water in tank A is the density times its volume. Generally speaking the more you pay, the more technical information you get. There is some friction loss in the fittings, let's assume that a conservative estimate is 30% of the pipe friction head loss, the fittings friction head loss is = 0.3 x 2.4 = 0.7 feet. The pump will operate (flow and head) where its performance curve intersects the system curve. The horsepower stated may or may not be corrected for specific gravity or viscosity. This is likely the most common and the most expensive mistake I witness in the field. The steps to follow to select a centrifugal pump are: To size and select a centrifugal pump, first determine the flow rate. For lower specific speed pumps the flow will be approximately 50 percent of rated and the head will be 60 percent of rated. A good example is weight lifting. The liquid is maintained in balance because the low pressure and the weight of the liquid is exactly balanced by the force of atmospheric pressure that is directed upwards. Load is calculated as follows: The discharge pressure depends on the pressure available on the suction side of the pump. You can preclude vortexing by the use of baffles and/or larger pipe diameters such as bell flanged inlets. OR The vertical distance from the surface of the fluid to the pump inlet is the submergence level. Denser liquids will have a value greater than 1 and lighter liquids a value less than 1. (( Plunger Diameter in inches)2 x p) x Pressure (psi) = Plunger Load (in pounds), Volumetric Efficiency compares the pumps actual output to its theoretical output. This phenomenon can occur at frequencies up to 300 times per second and at speeds near the speed of sound. All rights reserved. shown in these next figure. This field is for validation purposes and should be left unchanged. If you are at sea level the atmospheric pressure will be 14.7 pound per square inch absolute (psia), which translates (multiply by 2.31) into about 33.9 feet of absolute head. The total head is then 100 feet. The total head is the sum of the static head (remember that the static head can be positive or negative) and the friction head. The system curve represents all of the friction, static and pressure head baked into the system. Because I started my career in the submarine world, I have to point out that the speed of sound is even faster in salt water. The usefulness of specific gravity is that it has no units since it is a comparative measure of density or a ratio of densities therefore specific gravity will have the same value no matter what system of units we are using, Imperial or metric. A web app for pipe friction loss is available here https://www.pumpfundamentals.com/web-apps.htm, The performance or characteristic curve of the pump.

This a matter of taking measurements of the height between the suction tank fluid surface and the discharge pipe end height or the discharge tank fluid surface elevation. Compare two tanks with the same cylindrical shape, the same volume and liquid level, the tank with the denser fluid will have a higher pressure at the bottom. Example 1 - Sizing a pump for a home owner application. Understand cavitation.

When looking at pump applications, it is essential to mention three performance characteristics: crankshaft bearing life, volumetric efficiency, and inlet flow curve. Anywhere else on the published set of curves is simply a commercial compromise. This is a common comment, but it is subjective, not objective. Cold water is typically the worst fluid for the consequential damage from cavitation. Jim Elsey is a mechanical engineer who has focused on rotating equipment design and applications for the military and several large original equipment manufacturers for 47 years in most industrial markets around the world. All rights reserved. One shows the friction head on the discharge side and the other the friction head on the suction side. A typical value of friction loss for a check valve is 5 feet. For these reasons the pump manufacturers have chosen total head as the main parameter that describes the pumps available energy. Output may also be a function of the number of cylinders in a certain pump. This is a rather astonishing statement, here's why. The distance required to preclude air ingestion due to vortexing is the critical submergence level. Like in the straw, the pressure close to the pump suction connection must be low for the liquid to be supported. a lower velocity, for example between 4 and 7 feet/second. For the suction side of the pump, it is desirable to be more conservative and size pipes for Hopefully it will satisfy your appetite. Table 1 gives the flow rate and the friction head loss for water being moved through a pipe at a However, the curve does exist and if you insist you can probably get it. This is why buying a centrifugal pump is more complicated than buying a positive displacement pump which will provide its rated flow no matter what system you install it in. Why is this pressure less than atmospheric pressure or low? Note the speed of sound in air is approximately 768 miles per hour (mph) (1,236 kilometers per hour [k/h]) and varies somewhat with humidity levels. Normally these are gravity and/or atmospheric pressure. Those who would like to do pipe friction calculations can download an example here. Website Design: Cazarin Interactive.

I have chosen 10 ft/s as a target velocity because it is not too large If there is no loss in the pumping system, the flow would equal: It is difficult for the typical person to hold their hand on a bearing housing that is over 120 F. It is perfectly normal for a bearing to be operating at 160 to 180 F. Use a thermometer or infrared device to measure the temperature and deal Checking for factors like oil level and color can make a big difference. Horsepower requirements progressing along the pump curve change for different impeller geometries. For high specific speed pumps (axial flow), the highest hp required will be at the lower flows. NPSHa has nothing to do with the pump and should be determined or calculated by the system owner or end user. size on the suction side of the pump than on the discharge. The higher the margin, the better. If you continue to use this site we will assume that you are happy with it. Plunger Area (in square inches) x Pressure (psi) = Plunger Load (in pounds) Low and medium specific speed pumps require more hp the farther out on the curve you operate, which is fairly intuitive reasoning. Viscosity is the kryptonite of centrifugal pumps. Figure 30 shows a typical total head vs. flow rate characteristic curve. General Pump provides inlet flow curve charts for all its pumps on request. for a weight lifter but we will see how very useful it is for displacing fluids. We can calculate the discharge pressure of the pump based on the total head which we get from the characteristic curve of the pump. The vortexing phenomena is a direct function of the fluid velocity. Always check with the manufacturer when pumping viscous fluids for corrected curves and power limits for the frame, bearings and shaft. Jim Elsey helps you avoid common centrifugal pump mistakes, To read other articles in the 'Common Pumping Mistakes' column, go. This means that the pressure will be negative (relative to atmosphere) at the pump suction. People will erroneously think that because they have plenty of suction pressure or a flooded suction there is no reason to do these calculations. 231 in3 /gallon = gpm. The maximum realistic suction lift is about 26 feet. Critical submergence is necessary to prevent vortexing. One of the reasons is that they do not know how you will use the pump.

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