Presentation on theme: "Centrifugal and Submersible Pumps"— Presentation transcript:
1 Centrifugal and Submersible Pumps Don Davis, CIC
2 Pump Applications Centrifugal Pumps Submersible Pumps Booster applicationsOpen water applications (25’ maximum suction lift)Shallow well applicationsApplications where electrical lines can’t beinstalled in open waterSubmersible PumpsDeep well applicationsOpen water applications with suction lifts above25’Open water applications with excessive elevationrequiring higher output pressureApplications 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.
5 Internal Components Electrical motor Impeller Voltage, phase varies by applicationImpellerPlastic, cast iron, brass material optionsRotating 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 minuteFeet of HeadA 1’ high column of water contains the potential energy of 1’ of headThe 1’ high column of water will have a pressure of PSI at the baseFeet of head divided by = PSIPSI x 2.31 = feet of head
7 ExampleWhat is the pressure required to pump water to the top of a 25’ column?25’ / 2.31 = 10.8 PSI0r25’ x .433 = 10.8 PSI25’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 headInsufficient atmospheric pressure to push water into the impeller above 33.9’1 PSI loss for each 2000’ increase in elevation4000’ elevation would equal 12.7 PSI atmospheric pressure12.7 PSI x 2.31 = 29.3 feet of headRule 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 headSelection of pump should be ABOVE your specific design point on the curveSelection of a pump in the center of the curve is idealSystem design criteria is critical for pump selection
12 Calculating Feet of Head Vertical elevations: measure feetHorizontal distances: measure friction loss PSI, convert to feet
13 Friction Loss TablesFriction 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 PSI16.8 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 SelectionReducing 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 PSI4.45 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 bendsSize 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/fittingsInstall an isolation valve to aid in primingPressure relief valve/priming port should directly above dischargeInstall a union for maintenance purposesAdd filtration to all non-potable water sourcesInstall a pressure gaugeInstall a high temperature sensor, low pressure sensor
19 Proper installation using galvanized fittings. Avoid using PVC for direct connections to centrifugal pumps. Heat generatedduring operation or no-flow situations will cause problems!
20 Submersible Pump Installation Pump sled to include an inlet strainer and outlet well sealInstall union in discharge line near shore for maintenance purposesInclude safety line for retrievalInstall 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 spinSecure 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 SleeveA 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 desiredDoes not require pressure tank installationPump activates only when irrigation controller signals operation
24 On-Demand Pump Controls Pump Start Relay2 wire pumps can use a standard PSR3 wire pumps require a control box with start capacitorRefer to manufacturer’s cable sizing charts to determine wire gauge requirements
25 Pressurized Pump Systems Use in situations where a PSR is not feasibleMultiple controllers using same pumpQuick couplers or hydrants desired on siteController and pump are not in close proximitySpecial 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 ValveRestricts 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 CavitationFormation 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 lineMinimize fittings in suction lineReduce flow rate through pumpReduce suction lift elevationReduce suction line distanceCreate artificial pressure on the discharge by installing smaller diameter discharge pipe or throttling valve
32 Troubleshooting – All Motors MOTOR STARTS TOO OFTENCheck 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 necessaryPump intake blockedCheck valve stuck closedLow water level or loss of primeLeak in dischargeWorn 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 motorIncomplete priming of pumpAir lock in suction lineDrop pipe has disconnected from pumpLow water levelClogged or defective foot valve / strainerWorn 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 + ohmsExisting motor (without drop cable): 10,000,000 + ohmsNew motor in well: 2,000,000 + ohmsExisting 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 line3 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 damagedIf any one value is < normal, the motor is shortedIf any one value is > normal, the winding or cable is open / bad splice
39 Control Box-Ohm Tests Power OFF for ohm tests: Overloads should ohm less than 0.5Capacitor should ohm near 15,000Relay coil should ohmRelay contact should zero ohmStart 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 trippingOpen run capacitor: lower than normal red lead amps, and higher than normal yellow and black lead ampsFailed 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 sprinklersVertical elevation—water line to pumpVertical elevation—pump to highest pointMainline (size, type, length)Suction line (size, type, length)Well depth, yield, water level, pump set depthWell pump HP, GPM