Equipment Flashcards
Factors that can cause centrifugal pump cavitation
□ Too high suction lift
□ Partially plugged suction piping
□ High water temperature
□ Undersized suction piping
□ Partially closed suction valve
Distributes seal water uniformly around the pump shaft.
Lantern ring
“Rule of thumb” for leakage rate from pump packing.
One drip / second
The function of a shaft sleeve
Replaceable wearing surface that protects the pump shaft
A worn centrifugal pump impeller will result in this.
- Pump efficiency is reduced
- Pump output (pressure and flow) is reduced
This will occur if air is allowed to enter a centrifugal pump volute case.
The pump can become air-locked and refuse to pump.
Sludge greater than 1 % TS requires this kind of pump
Positive displacement pump
Key factor in operating any positive displacement pump.
Never operate the pump with a closed discharge valve.
Positive displacement pumps.
- Diaphragm
- Progressive cavity, Moyno™
- Piston
The way to correct wrong rotation in a three-phase motor.
Switch any two of the three electrical leads to the motor.
This pump shaft sealing mechanism utilizes a rotating carbon unit and a stationary ceramic.
Mechanical seal
The flow of electric current is measured in this unit.
Amperes or “amps”
Materials used to make pump packing.
Hemp, flax, jute, cotton, teflon,™ and graphite
These conditions can cause an operating centrifugal pump to fail to deliver water.
- Plugged impeller
- Closed suction or discharge valve
- Airlock in pump volute case
- Loss of prime
- Plugged suction or discharge piping
- Impeller not connected to shaft
Over lubrication of a bearing can result in this
Bearing overheating and failure
These symptoms may indicate bearing failure.
- Vibration
- Bearing noise
- Increase drive motor amperage draw
- Excess bearing temperature
The most common type of electric drive motor in the wastewater industry.
Synchronous speed
Typical causes of electric motor failure.
- Dirt
- Moisture
- Overload caused by bearing failure
Maximum practical pump suction lift.
25ft
Function of pump wearing rings
□ Prevent loss of efficiency due to pump internal recirculation
□ Replaceable, they protect the pump impeller and volute case from wear and damage
Piping colors:
brown
orange
green
blue
gray
yellow
purple
- Sludge
- Natural gas / digester gas
- Compressed air
- Water
- Wastewater
- Chlorine
- Reuse
Direct connection of potable water to water-using equipment in a wastewater plant or pumping station.
Hazardous cross connection
Functions of seal water piped to the pump stuffing box.
□ Cook rotating shaft and packing
□ Flushes grit and debris away from shaft and packing
□ Lubricates rotating shaft and packing
Impellers used in sewage pumps.
□ Designed to be “non-clog” with open, exposed impeller vanes
□ Non-clog characteristics sacrifice pumping efficiency
Methods used to determine tank or wet well water level.
- Bubbler tube
- Electrical probes
- Pressure transducers
- Ultrasonic transmitters
- Floats
Throttling the discharge valve on an operating centrifugal pump can stop this.
Cavitation
Expected flow when two pumps discharge into a common discharge pipe.
Due to friction losses, the two pump output will always be less than simply adding the output of each pump individually
Pump cavitation facts:
Basic cause
Problems associated with cavitation
Sound
Not a cause of cavitation
- Cavitation occurs when the eye of the impeller experiences excessive vacuum conditions causing water to flash into vapor
bubbles. - Vapor bubbles produced by cavitation collapse with tremendous force causing Pump noise, vibration and impeller damage.
- Cavitating pumps sound like they are pumping marbles or rocks.
- Entrained air bubbles never cause pump cavitation.
Evidence of pump impeller cavitation.
Symmetrical pitting and damage to impeller
Open channel flow measuring devices.
- Flumes
Palmer-bowlus (used in sewer manholes)
Parshall - Weirs
V-notch
Rectangular
Causes pump vibration or noise.
- Cavitation - sounds like rattling marbles or rocks
- Wrong rotation
- Misaligned pump and motor shafts
- Damaged or plugged impeller
Closed pipe flow measuring devices.
□ Magnetic Wastewater and sludge
□ Ultrasonic Wastewater
□ Venturi Wastewater
□ Propeller Effluent
Gas chlorinator fundamentals:
Vacuum condition
Flow control
Flow measurement
- Required for chlorinator operation. If water flow is reduced through the injector head venturi, the vacuum is reduced and the
chlorinator will shut down. - Chlorine gas flow is controlled by the position of a needle valve or v-notch plug.
- Gas chlorinators are equipped with a rotameter that reads in pounds per day.
Head - capacity (H-Q) pump curves plot these.
Total dynamic head in feet (meters) vs flow in gpm (liters/sec)
Lowering the total head that a pump operates against.
- Flow output of the pump increases
- Horsepower and amperage draw increase
Increasing pump speed affects this
- Flow goes up in proportion to the change in speed
- Pressure goes up
- Horsepower and amperage draw go up dramatically
Pump wrong rotation.
- Pump output is reduced
- Pump may be noisy or vibrate
- Corrected by swapping any two of the three 3-phase motor leads
Over lubrication of bearings is a common cause of this
Bearing failure due to excess heat
Pump station lead / lag pumps
Should alternate lead / lag status after each pumping cycle. If monthly run times differ dramatically, look for mechanical problems.
Electric motor “start amps.”
Can be 3-5 times the “running amps”
Functions of motor - pump shaft coupling.
- Dampen vibration caused by small misalignment
- Reduce bearing wear caused by small misalignment
- Transfer power from motor shaft to pump shaft
Steps to restore newly re-packed pump to service.
- Tighten gland nuts finger tight
- Restart pump
- Tighten gland nuts until leakage controlled but generous
- Allow packing to fully seat, then tighten glad to control leakage to desired amount
Pump total (dynamic) head
- Total static head plus suction and discharge friction losses expressed in feet (meters)
NPSH
- Net positive suction head (available atmosphere pressure at impeller eye during pump operation)
- To avoid pump cavitation the NPSH available must be greater than the NPSH required by the pump manufacturer.
SCADA
System control and data acquisition
Basic SCADA components.
- Supervisory system (computer)
- HML (human-machine interface) device that presents process data to operator
- Remote terminal units (RTUs) or Programmable logic controllers (PLCs)
- Communication system connecting computer to RTUs
- Various process and analytical instrumentation providing input to RTUs
Water hammer
Water hammer is the extreme pressure surge that results from rapid changes in water
velocity (slow down or speed up). Water hammer is of concern whenever water travels
in pipes at high velocity and/or high pressure.
Causes and cures for water hammer.
CAUSE
1. Opening or closing valves rapidly -9
2. Pump start to “instant” full speed =>
3. Pump shut off = 7
CURES
1. Slow opening / closing valves
2. Start pump against slow opening valve or utilize soft start pumps that ramp up to full speed
3. Activate slow closing valve prior to pump shut off
General rule for lubricating equipment
Use the lubricants and lubrication frequency specified by the equipment manufacturer.
total static head (TSH).
Vertical distance in feet (meters) from intake water level to discharge water level
