Q. How can rotation be checked if the pump is installed and unable to be removed?
A. There are three ways; the sound of the pump, the swirl in the water as the impeller rotates and an amp draw comparison. When turning the wrong direction the sound emanating from the pump is noisy and rough, not the silent hum of a submersible pump. If the water level in the well is down near the pump housing, you can observe at the swirl in the water, which takes on a mirror image of the impeller rotation, or you take an amp reading of the pump - Then switch any two of its lead wires - The impeller will change direction - Take another measurement - The lower of the two amp readings will typically be indicative of connections enabling the impeller to rotate correctly.
Q. How is the pump's flow rate calculated?
A. To calculate the pump's flow rate, best done when no water is running into the basin, operate the pump for a period of time, ideally 60 seconds, stop it and measure how many inches the water level dropped. Determine the gallons per inch for your basin size, examples being 12.2 gallons per inch for a 60" Dia. well and 17.6 for a 72", and multiply it by the drop in water level to calculate your estimated GPM. If your pump run time deviates from 60 seconds, go through the same calculation, only factoring in the ratio between the test times to 60 seconds to calculate your estimated GPM.
Q. How are rail system leaks detected?
A. If the water level in the wet well is down, rail system blow by can be readily seen by the water spray inside the basin as the pump runs, but if the water level is high the leak could be hidden from sight. In such a case your amp reading and flow rate with assist in helping you detect the presence of a leak; high amps near or greater than the pump's rating or a flow rate that is less than expected could be an indication that the pump is not properly seated.
Q. Should a submersible pump be totally submerged at all times?
A. Total submersion is not necessary when the pump is operating on an intermittent basis, but if running continuously, a pump having an air filled motor may require total submersion. For most oil filled motor designs total submersion would rarely be necessary.
Q. What is the optimum pump run time?
A. There is no established optimum run time but short cycling the pump should always be prevented. Although a pump may claim to operate up to 15 or more starts per hour, being used in such a manner would not be recommended as there could be negative secondary consequences associated with a pump activating every 4 minutes. The On/Off elevations and pump station's basin diameter should be designed for a minimal 1 minute pump operation, longer if possible. For a duplex station, a 10 starts per hour design is suggested with each full cycle being set up for a six minute on to on cycle time. Pump cycles of greater duration, even continuous operation, will only become an issue if a light duty pump not designed for a long operating cycles is being used.
Q. When does an unbalanced voltage or a voltage drop become a concern and what are the consequences?
A. An unbalanced voltage or large voltage drop are two situations that need to be detected and addressed when occurring at a pump station. A voltage unbalance occurs when a leg differs by more than 1% of the three leg average. When a significant voltage drop is seen upon the pump activation and is more than 5% below rated voltage, there would be a concern. In both of these situations the motor is going to operate outside its design parameters, which will lower its torque, draw higher amps, runs hotter and have a reduced service life.
Q. Have new submersible pump station with pumps which will not pump to design point of 200 gpm @ 65 Feet TDH. Shutoff head is about 90 feet TDH. Pumps have been checked for rotation, RPM (without load), Amps are lower than pump rating, power has been checked from the power company and from panel to pumps, pumps sent back to factory and checked in lab setting and met design point; pumps pump about 45 to 70 gpm with pressure readings on discharge piping @ between 12 and 14 psi (add about 5 to 8 psi for static and piping losses from wetwell. FM has been checked and air release stations appear to be working well. Any suggestions are appreciated.
A. This could be a good question to pass along to the SWPA membership. All parameters provided seem to be in line for a workable system. But your low pressure readings (51' actual vs. 65' design) could be reflective of the lower than expected flow rate being reported. My gut feeling would be to consider an obstruction in the force main; be it an air lock, collapsed pipe or other impediment to flow. To help more I'd need to know your recorded amp draws vs. the pump nameplate and see a system layout including dimensions of the pump station and force main. Finally, in wanting to consider any possibilities, make sure that there is no additional water flowing simultaneously into the basin through a low elevation inlet. This has fooled me before when checking a pump's flow rate and not being aware of an underwater inlet.
Q. Should I set the actual volt value measure on the phase monitor or the nominal? Ex measured 495 and the phase monitor is 480 VAC.
A. The recommended way to set the Phase Monitor is to measure the voltage, Phase to Phase, and set the adjustment knob to that setting. M.P. Electronics’ Phase Monitors for 480V applications are “true 480V” phase monitors, i.e. the center of the range is at 480V, with the adjustment range being from 425V to 525V.
Q. How do we determine if the signal is correct for seal leakage? And how is the sensor check at start up?
A. Checking the seal leakage signal at start-up is pump dependent. For Flygt Pumps, the sensor wires will have an impedance of app. 1500 Ohms when no leakage is present, and this drops to approximately 300 ohms when a leakage condition exists. The majority of pump manufacturers make a conductivity measurement using a probe to ground, or probe to probe setup to look for leakage as the water mixes with oil and allows for a measurement from one probe to ground or from probe to probe to occur. Several manufacturers have a test resistor between probes that measure 300K ohms when there is no indication of leakage. As a rule of thumb, oil is non conductive, so if all is well, i.e. no leakage or intrusion, you would read an extremely high impedance, or you would read 300Kohms for the pumps with the test resistor across their leakage probes.
Q. Does the dead front protect from Arc Flash?
A. The deadfront door does not protect from Arc Flash. The Arc Flash phenomena is a violent, explosion like condition. The deadfront door is a “finger-safe” safety feature for a control panel that allows the operators of the lift station to monitor and control the pumps by the switches and indicators on the outside of the door, while keeping themselves isolated from the control panel wiring just behind the door.
Q. Will checking of the direction of rotation bring any damage to the mechanical seal?
A. Damage to the shaft seal should not occur when checking the pump's rotation by momentarily starting it while being suspended in air to see what direction the momentum swings it. This is a very brief test, lasting less than 5 seconds. One note, with the power off, it's a good idea to rotate the impeller through a couple revolutions before activating the pump. This is particularly true for a pump that has been in storage. A manufacturer's service manual will, typically have instructions regarding their suggestions for keeping the pump's bearings and seals well lubricated while in storage.
Q. In 3 phase units are there ever any capacitors for low voltage usage?
A. For applications where 230VAC, single Phase is present, Single Phase Modules (SPM’s) are used to convert the 230VAC Single Phase power to 230VAC, 3-Phase power. The SPM’s consist of a Start Capacitor, a Run capacitor and a Start Relay. One leg of the incoming single phase power is run through the SPM to create a third phase. While SPM’s have been used for years, the 3-phase power developed this way is unbalanced, and pumps using it typically have low torque. The trend has been to use VFD’s rated for Single Phase input to get a balanced 3 Phase output, which allows the pump to have good torque, preventing clogging.
Q. Is there a minimum time between pump on cycle?
A. The fifth question addresses this question from a different perspective with a similar answer. Ideally, a pump should run for at least a minute, but more important, the system should be designed so that once it deactivates it stays off for 5 minutes. While a longer run time is preferred, it is more important to avoid a pump system that short cycles. A system designed to have 10 pump cycles per hour is suggested. Refer to question #5 for more details on this subject.
Q. What is the most frequent reason for a submersible pumps failure?
A. The most frequent reason for a pump failure is when the motor has a bad stature winding since that is when a problem gets magnified and the pump fails to operate and the problem is recognized. But there are many things that can cause a winding to fail, none more prevalent than the other. Some are:
- Having a voltage source issue such as unbalanced or undersized voltage supply, causing the motor to run hotter and reduce its expected service life.
- Water getting into the motor, causing the windings to eventually overheat and short out.
- Pump being overworked possibly from being a bad selection for the application, operating off its curve or pumping a liquid with higher than normal solids concentrations. In any of these situations the pump will be drawing higher amps, making the motor run hotter and shortening the life of the motor.
Having a means for monitoring the pumps performance and reacting to the first signs of a problem can prevent some motor failures but if left alone and not attended to the eventual result will be a failure of the motor.
Q. Would like to see some further information on RPac.
A. Bob, Schneider Electric has a information on this but I would also recommend doing an internet search for “remote programmable automation controller”. Here is a link that for some further information including data sheets: http://www.schneider-electric.com/products/WW/en/6000-telemetry-remote-…
Q. I'm not an EE, my background is Civil. However, I would like to learn more about the control side (e.g., SCADA, sensors, etc.) of pump stations. Can you recommend any good resource/guide/book for my purpose?
A.Here is a link to SWPA Specification and users for this topic: http://www.swpa.org/swpa/document_view.asp?id=5
Q. In remote locations without reliable cell phone service what are the options for remote monitoring?
A. Only option would be satellite.