NPSH where NPSHR known
Maximum Condensate Temperature
The maximum temperatures estimated by this calculator are derived from the Saturated Steam Properties table. The calculations presume that no additional pressure is provided from water in either the receiver (or tank) and/or the suction piping of the pump. Also assumes no friction loss for suction piping and no suction strainer in suction piping. Refer to the article Are Suction Strainers Necessary on Centrifugal Pumps?
Maximum Temperature at Pump's Required NPSH
The calculator estimates the maximum condensate temperature (°F) that a centrifugal pump can handle for various values of Net Positive Suction Head Required (NPSHR). A pump's NPSHR can be determined from a pump's Performance Curve that is provided by the pump manufacturer.
Figure 1. Example of a Shipco® pump performance curve.
Example A. In Figure 1, the NPSHR for the pump 129-D, 3500 RPM at a flow rate of 110 gpm is 2 feet NPSHR. The values for NPSHR are printed across the top of the pump performance curve.
Another important factor impacting maximum temperature that a pump can handle is the altitude. As altitude increases, the atmospheric pressure decreases. As atmospheric pressure decreases, the boiling point of water decreases. As a result, a pump that operates properly at sea level may experience cavitations at 2000 feet of elevation depending on the Available NPSH (NPSHA). NPSHA must exceed NPSHR to avoid pump cavitations.
Example B. At 2-foot NPSHR, water boils at 208.9°F at sea level, but 205.2°F for 2000 feet altitude (Note: values from calculator). For those accustomed to reading literature that states a pump can handle temperatures up to 210°F at 2-foot NPSHR, see Example C for explanation.
Example C. Why does pump literature typically state a maximum temperature of 210°F for 2-foot NPSHR at sea level?
In the real world, it is common to have 6-8 inches of water accumulated in the suction piping and bottom of receiver. The weight from this water (expressed in psi) when added to the NPSHA available at 2-foot NPSHR enables the pump to handle condensate temperature up to 210°F.
At sea level, the NPSHA at 2-foot NPSHR is 13.831 (i.e., 14.697 - 0.866), where 14.697 is the atmospheric pressure available at sea level and 0.866 is the NPSHR of the pump at 2-foot NPSHR). The corresponding pressure from the weight of eight inches of water is 0.325. This value is derived by converting feet of head to psi using the formula 1 psi = 2.31 feet of head. Adding 0.325 to 13.831 gives NPSHA of 14.156 psia. Looking up 14.156 in a Properties of Steam Table is relatively close to a temperature of 210°F.
View table of Saturated Steam properties.