Selecting/Installing the Right Pump


by Peter Gennaro

Camac Industries


The key to selecting the right pump is to gather as much data as possible relating to your application.  The data required can be classified into several categories.



The pump capacity is simply the volumetric flow rate expressed in suitable units such as gallons per minute, gallons per hour, etc.


Suction Piping

It is important to determine if the inlet piping is large enough for the required flow rate and whether the pump has enough suction lift to draw the solution up the required height.  Make sure there is adequate solution to avoid starving the pump and damaging the seals; if not, specify what method of priming will be used or select a self-priming pump.


Discharge Piping

This information is required to determine the total height the solution will be lifted (feet of head), taking into consideration all fittings, horizontal runs and pressures the pump will be working against (filters, spargers, spray assemblies, etc.)  Feet of head is another way of expressing pressure (Tables I and II).


Solution to be Pumped

In order to select the proper material of construction of the pump and make the correct seal selection, it is important to specify the temperature of the solution and concentration of the chemicals that make up the bath.  When making a seal selection, it should be noted if solids are present or if the solution crystallizes, in which case a water flushed seal would be required.

The specific gravity (ratio of the weight of a given volume of liquid to the same volume of water) and viscosity (thickness or resistance to flow) both affect the horsepower of the motor, discharge head and how the priming of the pump will be accomplished.


Duty Cycle

The duty cycle is important in determining the pump controls and piping.  It shows how the pump will be used when placed in service.



            Electrical requirements are to be specified to select the proper motor and ensure that proper electrical service is available.




Position of Pump

            These details relate to the physical layout and permit proper specification of pipe fittings to and around the pump.



            This once again relates to selection of the right motor for chemical, explosion-proof, drip-proof or totally enclosed applications.



            Now that you have purchased the correct pump for your application, it is important that the proper plumbing be installed to insure trouble-free service with a minimum of maintenance.  It should be noted that plumbing suitable for metal pumps may not be applicable for plastic pumps and may even cause damage to the pump.

            It is recommended that all piping to plastic pumps be properly supported to avoid applying stress on the pump.  A heavy unsupported pipe can exert enough leverage on a plastic pump to cause cracking and misalignment which will cause leaking and premature motor and seal failure.

            Upon completion of the piping, it is important that all inlet connections be inspected to make sure they are air-tight.  It should be noted that even the slightest air leak can cause the pump to run dry or overheat the seal cavity.  The use of teflon tape and joint compound will help to insure that all the connections are air-tight.

            Another area of importance when installing the piping is the number of fittings used between the pump suction and tank.  All centrifugal pumps should be installed as close to the tank as possible and the number of fittings (valves, strainers, elbows, tees) should be kept to a minimum.  Each fitting used will cause a slight pressure drop and the total of all the fittings used can cause enough pressure drop to reduce the flow to the pump to the point where premature seal failure will occur.

            When the pump is used to empty a tank, it is recommended that an automatic shut-off device be installed to stop the pump when the liquid being pumped has been exhausted to prevent the pump from running dry.  If it is impractical to use such a device, the pump should be equipped with a water flushed seal to avoid damage from running the pump dry.

            Several recommended piping installations are shown in Figs. 1 to 3.



            Once the pump has been properly installed, a maintenance program should be set up to ensure trouble-free operation.  Suction and discharge piping should be checked for leaks and seals for both leaks or built-up crystallization of solution around the seal cavity.  It is much less expensive to replace a set of seals than to have the pump fail and replace the entire pump or lose a tank full of solution.

            If the proper pump has been purchased and installed properly, then with periodic maintenance you can look forward to years of trouble-free operation.







Table I.  Water Pressure to Feet Head


     Pounds Per                                          Feet                                     Pounds Per                                               Feet

     Square Inch                                        Head                                     Square Inch                                             Head


                1                                                  2.31                                              100                                   230.90

                2                                                  4.62                                              110                                   253.98

                3                                                  6.93                                              120                                   277.07

                4                                                  9.24                                              130                                   300.16

                5                                                11.54                                              140                                   323.25

                6                                                13.85                                              150                                   346.34

                7                                                16.16                                              160                                   369.43

                8                                                18.47                                              170                                   392.52

                9                                                20.78                                              180                                   415.61

              10                                                23.09                                              200                                   461.78

              15                                                34.63                                              250                                   577.24

              20                                                46.18                                              300                                   692.69

              25                                                57.72                                              350                                   808.13

              30                                                69.27                                              400                                   922.58

              40                                                92.36                                              500                                 1154.48

              50                                              115.45                                              600                                 1385.39

              60                                              138.54                                              700                                 1616.30

              70                                              161.63                                              800                                 1847.20

              80                                              184.72                                              900                                 2078.10

              90                                              207.81                                            1000                                 2309.90


NOTE:     One pound of pressure per square inch of water equals 2.309 feet of water at 62°Fahrenheit.  Therefore, to find the feet head of water for any pressure not given in the table above, multiply the pressure pounds per square inch by 2.309.


Table II.  Feet Head of Water to PSI


     Pounds Per                                          Feet                                     Pounds Per                                               Feet

     Square Inch                                        Head                                     Square Inch                                             Head


                1                                                    .43                                              100                                     43.31

                2                                                    .87                                              110                                     47.64

                3                                                  1.30                                              120                                     51.97

                4                                                  1.73                                              130                                     56.30

                5                                                  2.17                                              140                                     60.63

                6                                                  2.60                                              150                                     64.96

                7                                                  3.03                                              160                                     69.29

                8                                                  3.46                                              170                                     73.63

                9                                                  3.90                                              180                                     77.96

              10                                                  4.33                                              200                                     86.62

              15                                                  6.50                                              250                                   108.27

              20                                                  8.66                                              300                                   129.93

              25                                                10.83                                              350                                   151.58

              30                                                12.99                                              400                                   173.24

              40                                                17.32                                              500                                   216.55

              50                                                21.65                                              600                                   259.85

              60                                                25.99                                              700                                   303.16

              70                                                30.32                                              800                                   346.47

              80                                                34.65                                              900                                   389.78

              90                                                38.98                                            1000                                   433.00


NOTE:     One pound of pressure per square inch of water equals 2.309 feet of water at 62°Fahrenheit.  Therefore, to find the feet head of water for any pressure not given in the table above, multiply the pressure pounds per square inch by 2.309.



A.      Discharge is in the top horizontal position.  This is done to avoid any air pockets in the pump.

B.       Flooded suction.

C.       Inlet to pump should be at least ½” larger than inlet of pump.

D.      Water flushed seal is recommended if there is a chance that tank could be drained completely causing damage to seal by running the pump dry.

Fig.1.  Installation No. 1: Excellent


A.      On many applications it is desirable to use a hand valve or automatically operated valve on the discharge line.  It is the nature of a centrifugal pump to generate heat within the volute case when the valve is closed or throttled back.  This heat can be enough to cause damage to the seal.  To avoid this, a ¼” bleed line should be installed as shown above to dissipate the heat generated.

B.       When a valve is used and a bleed line is not practical, the pump should be installed with a water flushed seal.  This will prevent the pump from overheating and protect the pump should the valve be closed with the pump running.

C.       See A through D in Fig. 2.

Fig. 2.  Installation No. 2: Excellent


A.      As per the above diagram, install a foot valve and priming tee and make sure the pump is fully primed before starting.

B.       Install a liquid level control to avoid running the pump dry and have the pump equipped with a water flushed seal for extra protection.

C.       See A and C in Fig. 2.

Fig. 4. Installation No. 3: Very Good