TheР’В other item to point out is that the pumping cost per 1,000gpm decreases rapidly but the savings decrease withР’В increasing pipe diameters. As you can see from thisР’В graph, sizing the discharge pipeline to match the pumps discharge flange is not the most economical choice. Graph 1 shows how changing the nominal pipe diameter affects the pumping costs. ManufacturerРІР‚в„ўs supplied pump curve for pump used in the example system. Next weРІР‚в„ўll calculate the power cost needed to pump 1,000m3 of water at 15РІВРЉ through a 150mm pipe usingР’В Formula 1.Р”Р‡igure 2. To check this result, we can see from the pumpР’В curve that a flow rate of 171.9m3Р’В rate through the system is such that the head produced by the pump is equal to the head consumed by theР’В process and control elements. Adding the head loss of the pipeline with the systemРІР‚в„ўs static head ofР”В¦2m results in a head of 103.97m for the process and control. The resulting flow rate through the system is 171.9m3Р’В 41.97m of fluid in the discharge pipeline. This is the same diameter as theР’В discharge flange on our pump. When the supplyР’В tank is pumped down, the pump shuts down to prevent the pump from running dry when the supply tank is fullР’В the pump is turned on.Р”Р„s a result, all the energy supplied by the pump is used to move the fluid through theР’В process elements.Р’В Now that we have the three elements defined, letРІР‚в„ўs see how a change in the pipe diameter effects the flow rateР’В through the system.Р”Р‡irst we will look at the system with a 150mm nominal size discharge pipe. We will vary the pipe diameter to demonstrate how a change in the pipe diameter affectsР’В the flow rate through the system.Р”Р‡inally, the control elements of the system consist simply of an on/off control for the pump. The discharge pipe is 1,200m in length made ofР’В steel schedule 40 pipe. A short 350mm diameter pipelineР’В serves as the pumpРІР‚в„ўs suction line with insignificant head loss. The destination tank has a liquid level of 62m above the common datum. The process elements consist of the supply tank, with a liquid level of zero metres above the common datum. Based on the manufacturerРІР‚в„ўsР’В information, the pump suction flange is eight inches in diameter (200mm) and the pump discharge flange is sixР’В inches in diameter (150mm), with the eleven inch (279mm) indicating the pumpРІР‚в„ўs maximum impeller diameter. The pump curve used in this example can be found in Figure 2.

In this example system the pump is an end suction design with a manufacturerРІР‚в„ўs identifier of 8Р“вЂ”6Р’В11, operatingР’В at 3,000rpm. Control of the system is achieved by turning the pump off when not required. Layout of the example piping system showing the pump and process elements. In this article weРІР‚в„ўll discuss why his rule of thumb may be costly.Р”Р„ piping system is made of three elements: the pump elements, adding all the fluid energy the processР’В elements, making the product or providing the service and the control elements, improving the product quality.Р’В Figure 1 shows the system details.Р”Р‡igure 1. He said his rule of thumb was to size the discharge pipe to that of the pumpРІР‚в„ўs discharge flange.Р”Р‡or example, if the pumpРІР‚в„ўs discharge nozzle was 150mm, he would use a 150mm nominal size pipe for hisР’В discharge header. When we covered the material on pipeline sizing, the dewatering engineer asked why we needed to performР’В this calculation. He mentioned they were mountedР’В on a semiР’Вtrailer so they could be moved around the mine, along with a second semi for the diesel electric powerР’В supply.Р”В®ven though they were in the desert, all the rainfall would run off the ground resulting in flash floods thatР’В could quickly collect in the mine causing a disruption in production.Р”Вuring the course of the training, when I discussed system static head, I made a point that the static head ofР’В the dewatering system amounted to the difference in elevation between the water level at the bottom of the mine,Р’В to the elevation of the end of the discharge piping. I then went around the room asking each attendee what they did at the facility andР’В what they hoped to get out of the course.Р”В®ach attendee had a specific topic of interest and I remember theР’В dewatering engineer saying his goal was to improve the operation of the dewatering pumps.Р”В«eing that the mine was in the desert, I asked him how big the pumps were.

IР’В was teaching a Piping System Fundamentals course at an open pit copper mine and mill in the southР’ВwesternР’В United States.Р”Вuring my introduction I stressed the importance of understanding how the individual items of aР’В piping system work together. Ray Hardee shares his insights into how choosing theР’В right size discharge pipe can reduce operating time and costs. By Ray Hardee, Chief Engineer, Engineered SoftwareР”В¬hoosing the size of a pump discharge pipe can be a complicated process, with aР’В range of factors to consider.

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