1. Centrifugal and Submersible Pumps
Don Davis, CIC

2. Pump Applications Centrifugal Pumps Submersible Pumps
Booster applications
Open water applications (25’ maximum suction lift)
Shallow well applications
Applications where electrical lines can’t be
installed in open water
Submersible Pumps
Deep well applications
Open water applications with suction lifts above
25’
Open water applications with excessive elevation
requiring higher output pressure
Applications where a visible pump is undesirable

3. Centrifugal Pump Operation
How does a pump….pump?
An airtight intake creates a vacuum during impeller rotation.
14.7 psi of atmospheric pressure exists at sea level. This is the pressure pushing water into the impeller.
(Atmospheric pressure decreases 1 psi for each 2000 feet increase in elevation)
The spinning impeller creates inertia, increasing pressure and discharging the water.

4. What’s Inside?

5. Internal Components Electrical motor Impeller
Voltage, phase varies by application
Impeller
Plastic, cast iron, brass material options
Rotating impeller pushes water against pump casing or volute and increases pressure.
Add more impellers to increase pressure and create a multi-stage pump (that is how a ¾ horsepower pump in a 1000 foot deep well can supply water)

6. Pump Terminology Horsepower Feet of Head
Power required to lift 33,000 pounds or 3750 gallons of water 1 foot in one minute
Feet of Head
A 1’ high column of water contains the potential energy of 1’ of head
The 1’ high column of water will have a pressure of PSI at the base
Feet of head divided by = PSI
PSI x 2.31 = feet of head

7. Example
What is the pressure required to pump water to the top of a 25’ column?
25’ / 2.31 = 10.8 PSI 0r
25’ x .433 = 10.8 PSI
25’
How much pressure do we have at the top of the column?

8. Maximum Suction Lift How does this affect pump applications?
Convert 14.7 PSI at sea level to feet of head:
14.7 PSI x 2.31 = 33.9 feet of head
Insufficient atmospheric pressure to push water into the impeller above 33.9’
1 PSI loss for each 2000’ increase in elevation
4000’ elevation would equal 12.7 PSI atmospheric pressure
12.7 PSI x 2.31 = 29.3 feet of head
Rule of thumb: DO NOT exceed 25’ suction lift

9. Pump Curve Data Curve provides performance data for a specific pump
Curve notes GPM the pump provides at a specific feet of head
Selection of pump should be ABOVE your specific design point on the curve
Selection of a pump in the center of the curve is ideal
System design criteria is critical for pump selection

10. Pump Curve - Centrifugal

11. Pump Curve - Submersible

12. Calculating Feet of Head
Vertical elevations: measure feet
Horizontal distances: measure friction loss PSI, convert to feet

13. Friction Loss Tables
Friction loss tables provide the PSI loss per 100 feet of pipe at a given flow.
Larger diameter pipe results in lower PSI loss at the same flow.

14. Calculating Feet of Head
Assume system requirements are 12 GPM at 50 PSI:
Suction lift (assume submersible for this example) 0’
Elevation change from pump to highest point on site 17’
Mainline friction loss (500’ of 1” SCH 40, 12 GPM) 38.8’
3.36 PSI loss/100 feet * 500 feet mainline = 16.8 PSI
16.8 PSI * 2.31 = 38.8’
Desired operating pressure of 50 PSI converted to feet: 115.5’
50 PSI * 2.31 = 115.5’
Total Feed of Head ’
Will need to use the 1 hp submersible from the pump curve

15. Pump Selection
Reducing feet of head requirements may allow selection of smaller pump. Take the previous example:
Suction lift (assume submersible for this example) 0’
Elevation change from pump to highest point on site 17’
Mainline friction loss (500’ of 1 ¼ ” SCH 40, 12 GPM) 10.2’
0.89 PSI loss/100 feet * 500 feet mainline = 4.45 PSI
4.45 PSI * 2.31 = 10.2’
Desired operating pressure of 45 PSI converted to feet: 103.9’
45 PSI * 2.31 = 115.5’
New total feet of head: ’
Can use the ¾ hp submersible from the pump curve

16. Proper Plumbing - Suction
Most pumps fail due to improper plumbing on the suction side.
Minimize fittings and bends
Size the suction line 1-2 pipe sizes larger than the inlet thread size.
Make it as short as possible.
Use a straight, level length of pipe into the suction. (length = 5-10 times the pipe diameter)
Foot valve/strainer must be in clean water.

17. Proper Plumbing - Discharge
Discharge plumbing tips:
Use galvanized pipe/fittings
Install an isolation valve to aid in priming
Pressure relief valve/priming port should directly above discharge
Install a union for maintenance purposes
Add filtration to all non-potable water sources
Install a pressure gauge
Install a high temperature sensor, low pressure sensor

19. Proper installation using galvanized fittings.
Avoid using PVC for direct connections to centrifugal pumps. Heat generated
during operation or no-flow situations will cause problems!

20. Submersible Pump Installation
Pump sled to include an inlet strainer and outlet well seal
Install union in discharge line near shore for maintenance purposes
Include safety line for retrieval
Install check valve in suction line

21. Submersible Pump Installation
Pump sled can be constructed from PVC pipe and fittings.
Use galvanized (or stainless steel) fittings between the pump and discharge pipe. Pump start-up torque WILL unscrew the pump from PVC fittings!
Well seal prevents torque spin
Secure wiring to discharge pipe. Leave excess wire at shore line for maintenance purposes.
Install isolation valve upstream of pump for troubleshooting purposes.

22. Pump Sled or Sleeve
A casing is mandatory for a submersible pump! The water intake is located above the motor. Placing the pump in a casing forces all of the intake water to pass over the motor for cooling purposes.
A pump left in open water WILL overheat.
Cistern or dock applications: install pump inside a sleeve.

23. On-Demand Pump Systems
Use in situations where a continuously pressurized mainline is not desired
Does not require pressure tank installation
Pump activates only when irrigation controller signals operation

24. On-Demand Pump Controls
Pump Start Relay
2 wire pumps can use a standard PSR
3 wire pumps require a control box with start capacitor
Refer to manufacturer’s cable sizing charts to determine wire gauge requirements

25. Pressurized Pump Systems
Use in situations where a PSR is not feasible
Multiple controllers using same pump
Quick couplers or hydrants desired on site
Controller and pump are not in close proximity
Special requirements:
Shelter large enough to accommodate pressure tank(s)
Drain to exterior for PRV

26. Pressurized Pump Controls
Size bladder tank at minimum one gallon drawdown for each GPM of pump capacity. Multiple tanks can be installed in series for higher GPM requirements. Set tank pressure at 2 PSI below pump cut-in pressure.
Tank tee allows for pressure switch, pressure gauge, pressure relief valve, drain valve, and check valve installation in a compact location.

27. Varied GPM Requirements
Cycle Stop Valve
Restricts pump output to match GPM demand. As demand decreases, the Cycle Stop Valve increases back pressure on the motor. Increased back pressure decreases the gallon requirement. This decrease in gallon requirement reduces the load on the motor, resulting in reduced amperage draw and therefore power consumption.
Pressure downstream remains constant within the allowable flow rates for the particular unit.
Byproduct of Cycle Stop Valve operation is the elimination of water hammer.

28. Varied GPM Requirements
Variable Frequency Drive Motor (VFD)
Varies the frequency and voltage supplied to an electric motor. As frequency (or hertz) increases, motor RPM increases.
While a standard motor will operate at full RPM regardless of GPM demand, a VFD has potential for energy savings when operating at a lower frequency during lower GPM demand.
3 phase motor required

29. Cavitation
Formation of air bubbles in a liquid that occurs when the pressure falls below the vapor pressure.
The vapor will turn back to a liquid and ‘explode’, causing damage to the components.

30. Preventing Cavitation
Increase net positive suction head (NPSH) available by:
Increase the diameter of suction line
Minimize fittings in suction line
Reduce flow rate through pump
Reduce suction lift elevation
Reduce suction line distance
Create artificial pressure on the discharge by installing smaller diameter discharge pipe or throttling valve

31. Cavitation Damage
Brass Impeller

32. Troubleshooting – All Motors
MOTOR STARTS TOO OFTEN
Check setting on pressure switch. Reset limit or replace switch.
Damaged or defective check valve will not hold pressure.
Check for waterlogged pressure tank. Change air charge or replace tank.
Examine system for leaks and repair as necessary.

33. MOTOR RUNS CONTINUOUSLY
Check pressure switch for welded contacts; adjust settings as necessary
Pump intake blocked
Check valve stuck closed
Low water level or loss of prime
Leak in discharge
Worn pump: symptoms similar to low water level or drop pipe leak; reduce pressure switch setting and pump will shut off indicates warn parts

34. PUMP DELIVERS LITTLE OR NO WATER
Low line voltage to motor
Incomplete priming of pump
Air lock in suction line
Drop pipe has disconnected from pump
Low water level
Clogged or defective foot valve / strainer
Worn pump parts or plugged impeller

35. Circuit Breaker, Fuse, Overload Trips
Check for correct line voltage.
Overheated control or starter may require ventilation.
Defective control box.
Defective motor or cable.
Worn pump or motor.

36. Insulation Resistance Test
Ohm reading < 500,000 indicates insulation damage.
With power off and motor leads disconnected, test resistance between any one of the motor leads and equipment ground. A normal ohm value for all leads indicates the motor is not grounded and the cable insulation is not damaged.
New motor (without drop cable): 20,000,000 + ohms
Existing motor (without drop cable): 10,000,000 + ohms
New motor in well: 2,000,000 + ohms
Existing motor in well: 500,000 – 2,000,000 ohms

37. Winding Resistance Test
Refer to manufacturer’s charts for ohm values.
2 wire motors: measure resistance from line to line
3 wire motors: measure resistance Y to B (main winding) and Y to R (start winding)
If all ohm values are normal, motor is not grounded and cable insulation is not damaged
If any one value is < normal, the motor is shorted
If any one value is > normal, the winding or cable is open / bad splice

38. Control Box Schematic

39. Control Box-Ohm Tests Power OFF for ohm tests:
Overloads should ohm less than 0.5
Capacitor should ohm near 15,000
Relay coil should ohm
Relay contact should zero ohm
Start and run capacitors should ohm near zero and then move toward infinity

40. Control Box-Amperage Tests
Motor under load for amperage tests:
Red lead current should start high and then fall to manufacturer’s chart reading. Black and yellow lead current should not exceed chart reading.
Relay or switch failure: Constant high red lead current and overload tripping
Open run capacitor: lower than normal red lead amps, and higher than normal yellow and black lead amps
Failed start capacitor or open switch / relay: red lead current is not momentarily high at starting

41. Review Water source type Minimum and maximum flow, GPM
Desired pressure at sprinklers
Vertical elevation—water line to pump
Vertical elevation—pump to highest point
Mainline (size, type, length)
Suction line (size, type, length)
Well depth, yield, water level, pump set depth
Well pump HP, GPM