Operating Instructions

Transcription

1 Operating Instructions Note: 1. Never let the centrifugal pump run dry. 2. Make sure that there is at least one open path for water flow in the pipe network before turning the pump on. Never run the pump when all outlet valves are closed. 3. Be careful when closing valves while the pump is running. Always make sure that there will still be at least one open path for the water flow after you close a valve. Otherwise, you may: Damage the pump and/or Damage the pressure gauges by a shockwave caused by a sudden stop of the water flow. 4. Most of the valves in the Fluid Flow system are ball valves. To open a ball valve, rotate its handle so that it is aligned with the pipe. To close a ball valve, rotate its handle so that it becomes perpendicular to the pipe. Figure 1. Piping around the pump and the rotameter. 1. Configuring and starting the system a. There are three sources of water in the system: The building water supply The holding tank on the 1 st floor The holding tank on the 3 rd floor 3-1

2 Most of the time, you will be using the tank on the 3 rd floor for your source of water. The tank on the 1 st floor can be used to experiment with effects of low NPSH on the pump performance. The building water supply should only be used to refill the tanks. b. Select a tank for your water source and decide on the path for water flow. Water should flow from the selected source, into the pump, and through the rotameter. After it leaves the rotameter, water can be either recirculated back to the supply tank (this is useful for measurement of the pump characteristic curve) or sent through the pipe network first and then recirculated back to the supply tank. c. Trace the selected path for the water flow and make sure that all valves are in the correct position (open or closed) for the flow to follow your selected path. d. Once the valves are configured correctly, the pump can be turned on by simply pressing the button for its power supply (see Figure 1). 2. Rotameter calibration a. Make sure that the 1 st floor tank is about half-full. b. Record the volume of water in the 1 st floor tank. The volume graduations are on the back of the tank. Note that it is difficult to see the graduations if the tank is less than half-full. c. Configure the system so that water follows the following path: 3 rd floor tank pump 1 st floor tank. d. Turn the pump on and adjust the globe valve until a desired flow rate is achieved. e. Record the change in the water volume ΔV in the 1 st floor tank over a period of time Δt (recommended value of Δt is 30 to 60 seconds). Use a timer to measure time. f. Turn the pump off. g. Calculate the flow rate of water through the system as Q = ΔV/Δt. h. Repeat the above steps for several flow rates and create a table of the rotameter readings vs. the actual flow rate. 3. Measurement of characteristic curves of the pump and globe valve a. To obtain the pump and valve characteristic curves, water should be recirculated back to the feed tank without going through the pipe network. This allows one to investigate a wider range of water flow rates (since sending water through the pipe network will lead to additional friction losses and, hence, smaller maximum flow rate that can be generated by the pump). b. Use the globe valve and the rotameter (see Figure 1) to adjust and measure the water flow rate. c. To measure the pressure change across the pump, use pressure gauges installed at the pump suction (inlet) and discharge (outlet), see Figure

3 d. Use the differential pressure gauges installed on the railing of the pipe network to measure pressure drop across the globe valve. (Instructions for these pressure gauges are provided below). e. Record dependence of the flow rate, pressure change across the pump, and pressure drop across the globe valve on the number of rotations of the valve handle. (The valve handle contains a dial displaying the number of rotations; zero rotations correspond to a fully closed valve). 4. Measurement of a characteristic curve of a ball valve a. Inspect the pipe network and find a ball valve with pressure ports located near its inlet and outlet. b. Adjust other valves in the system to allow fluid flow through the selected ball valve. Make sure that only one branch of the pipe network is open. c. Fully open the globe valve and the selected ball valve and turn on the pump. d. Measure the flow rate using the rotameter and the pressure drop across the selected ball valve using a differential pressure gauge, as descried in the next section. e. Repeat the previous step with the ball valve being only partially open: rotate the valve handle so that it forms an angle with the pipe direction. Recommended angles are 30 o, 45 o, and 60 o. 5. Differential pressure measurement using the analog pressure gauges. The analog differential pressure gauges are installed on the railing of the pipe network (see Figure 2). These pressure gauges are preferred over handheld digital manometers, since the latter tend to malfunction after prolonged exposure to water. a. Select a pressure gauge to be used. There are two pressure gauges connected to the pipe network, each with a different maximum pressure. Pressures above this maximum value cannot be measured. b. Identify manometer tubes connected to the high and low pressure ports of the pressure gauge. Connect the tubes to the pressure ports on the piping network. The pressure gauges will report meaningful results only if he tubes are connected in the correct order (i.e., the high-pressure tube is connected to a pressure port with higher pressure). If the pressure gauge is not displaying a reading, try switching the tubes. 3-3

4 Figure 2. Analog differential pressure gauge. c. The tubing must be fully filled with water in order to obtain accurate readings. Therefore, before taking pressure readings, it is necessary to vent air bubbles from the tubes by opening the drain valves (located below the pressure gauges) for a few seconds and allowing some water to drain. If you don t see any water flow from the drain valves, this means that the water pressure is too low to push air bubbles out of the tubing. In this case, temporarily increase the water flow rate (and, hence, pressure) in the pipe until you see water draining from both drain valves. Close the drain valves after a few seconds of draining. d. To measure gauge pressure at a single point, connect the high pressure manometer tube to the corresponding pressure port. Keep the second manometer tube open to the atmosphere. e. Place the manometer tubes back onto the white rack (see Figure 2) after your measurement is complete. Do not hang them by the clips of the connectors, since this will damage the connectors. 6. Pressure measurement using the handheld digital manometer Important: The analog manometers (see above) are preferred over the digital manometer, since the latter may malfunction after prolonged exposure to water. a. Re-zero the manometer prior to measuring pressure: Leave both ports of the manometer open to atmosphere. Turn the manometer on by pressing the ON key. Press and hold the HOLD/MEMORY key until CLR appears on the screen. Then press the ZERO/HOLD key. 3-4

5 b. Vent air from the plastic tubes connected to manometer. This can be done, e.g. by connecting one end of a tube to a pressure port on a pipe while leaving the other end open to atmosphere. Water flowing through the pipe will displace air in the tube. c. To measure differential pressure between two points, connect the manometer ports marked HIGH and LOW to the ports on the pipe network corresponding to high and low pressures. The tubing must be filled with water in order to obtain accurate readings. Note: If HIGH and LOW are switched, the digital manometer will report a negative value. d. To measure gauge pressure at a single point, connect the manometer port marked HIGH to the corresponding pressure port on the pipe. Keep the second manometer port open to atmosphere. e. Refer to the manufacturer s manual posted on the course website for information on other features of this manometer, including the Hold and Memory functions. 3-5