The Pump shown here is a 4E Series 1510 Centrifugal Bell & Gossett Pump. It is designed for 500 GPM @ 85 FT of head with an RPM of 1750. The impeller size should be a 10". The motor is a 20 HP at 1750 RPM. All of this information should be taken from the manufactures submittal data sheets. Now we need to make sure that the pump we have submittals for matches the pump that was installed. There will usually be a metal plate on the base of the pump mount that will have model #, serial #, impeller size, design GPM, and Pressure Drop stamped on it. Next check the motor tag for correct motor size and voltage. If all this information is correct then you are now ready to take pressure drop readings
across the pump. Your readings will need to be measured in feet. If the meter or gauge you are using measures in something other than feet then you will need to convert your reading HERE. The first reading we are going to take is called the Dead Head reading. This is done by fully closing the Discharge Valve with the pump running. "Make sure you do not close the suction / return valve. You could cause major damage to the pump!" Also remember not to leave the discharge valve closed for any longer than needed to get your reading. For this example we are going to say that our dead head reading is 100 FT. Now we will need to take that reading and plot it on the submittal pump curve.
We now have figured out that we have all the correct data and impeller size. We also have our line drawn on the grid that we will use to balance out the flow. At this point with our discharge valve wide open remeasure the pressure drop and check the motor amps to make sure that we are not over amping. Remember that an increase in flow (or work) will have an increase in amps. Lets take a look back at the curve to see how much flow 75 FT. will produce.
The valve open reading when plotted on the curve was 625 GPM and our design is 500 GPM. Take a look at the pump curve a final time to find out what the correct pressure drop needed to give us design gpm.
Keep in mind when balancing your pump to set the flow on the high end of the design. This is due to pipe friction, and equipment pressure loss that could cause lower flow farther away from the pumps. Once your pump flow has been set it is also a good idea to recheck your motor amps. You are now ready to learn more about chillers in the next tutorial.
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