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We have a cistern in our parking lot we've had a 2 hp, 480 V, 2 1/2 inch/3 inch sewage pump for dewatering for a few years. Recently the pump cracked the 3 inch schedule 80 PVC that connected it to 10 foot 3 1/2 inch hose slipped into a 8 inch gravity drain pipe that leads to the storm sewer. We thought the crack occurred due to torque so we installed a soft start on the system within a few days we noticed we still weren't getting results so we installed a brand-new pump which worked fantastic for about a week and then it started doing the same thing the old pump was doing, running jumping around and not pushing a lot of water. We removed the soft start installed a pump of a different brand fired it up it also seemed to run excellent. (For about a week) Needless to say all this time we are checking voltages , amperage and resistances, all on point and well within the parameters of the pump specs. The pump is at the bottom of the well, clean cement bottom and always has approximately 4 feet of water above the pump. All lines are clear ,gravity feed line is clear nevertheless all three pumps 2 Zoeller and little giant went went through  parts of their windings. There are no check valves in the system and the head is approximately 11 feet which is also within the pump's minimum specifications. Any advice would be welcome we are actually dewatering with little giant  1-1/4 sump pump with corrugated pool hose tucked into the 8 inch gravity line. Thinking about wiring it up permanently.

Tags: premature, Sewage, failure, pump

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Please clarify your problem, is it a pipe cracking or pump performance or winding failure? Need the exact model of pump to identify proper pump performance. Is system 3 years old before failures? There are no hand valves, T's 90's 45's in the system?

What is the flow rate you are trying to obtain? You need to be as close to the performance line as possible If the 11' is too far left of the curve the pump can cavitate cause vibration and crack pipe or fail winding. 

It sounds like to me.....a possible system issue. There is typically a big difference in pump output from 1 1/4 to 2 1/2/3" pumps. The size of your discharge pipe is so big it offers very little "system" back pressure so you are working with primarily vertical rise.

Place a valve in the discharge of the pump somewhere and crack the valve open slightly, start the pump. The valve will be the "false head" needed to put back pressure on the pump and move the water, need curve to verify my explaination

Dave

RM

We realized the pipe cracking was a symptom of something more we thought it was just torque hence the addition of the soft start. We realize later that once a section of the windings had gone even with the motor running the pump started bouncing around in the bottom of the like an asphalt compactor. So we switched to Zoeller pump number two model G295 – D (same as the first installed by the pump company) and in a week had the same problem assuming it was the soft start creating the problem we removed it. Rewired the same as the 3 previous, problem free years and installed a little giant model 20S – CIM again maybe got a week. Throughout this whole process voltage, amperage, and impedance have been checked thoroughly. Mathematically the pit only holds about 1400 gallons of water when at level which the pump will evacuate approximately a thousand gallons in five minutes. Leaving the pump in 3 to 4 feet of water. 10 foot of head is in the little Giants curve. Were thinking electrical only because the physical properties haven't changed years. Our original problem three years ago was 4 feet of muck in the bottom of the pit master a few changes in drainage it's now clean as a whistle.

RM

So 1000 gpm 5 min =200 gpm required, do you know if you have 3 phase or 1 phase wiring

Little Giant pump model you supplied, below is "single phase 3 wire cord" note N/R means not recommended to operate in this range

Below is the "three phase 4 wire cord" curves, it too states 10' is N/R, depending on model of pump

Is the pump removing the water from the pit? Are you verifying the correct direction of rotation before you put pump in the pit? Do you have any upside down "U's" in you discharge pipe where air can get trapped? Is your pit vented to atmosphere? Your math may work on paper but in the field you have to prove your math works

Dave

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RM

The pump is removing water from the pit ,the pit is vented to the atmosphere. The pump is three-phase 480. There is no requirement on how fast the water is removed from the pit. My problem is this thing worked for years without a hitch and we lost the pump because of the huge amount of debris gravel and dirt in the bottom of the pit, replaced it with the Zoeller (same pump that was in there) three years ago after solving the debris issue. And it had no issue for three years, this all started after a cracked discharge line that we repaired, installed the soft start to relieve the torque. Went through the windings of 2 pumps, removed the soft start, installed the little giant and went through it in a week. At this point were not even sure if the soft start was the issue were still thinking another electrical issue because all the physical properties of the pump the pit the discharge haven't changed 15 years. We just don't know what it could be line spikes brownouts single phasing. We run a fairly large factory with over 200 pieces of equipment press brakes spot welders CNC punches the pump is the only thing that runs when our doors are closed ??? 

RM

Because I forgot to answer the question there are no loops traps or check valves for air to get trapped into , Just a straight shot up from the pump through the hose which is tucked into the 8 inch gravity feed line about 5 feet and runs downhill approximately 9 inches and 65 feet to atmosphericly vented cistern, part of the storm sewer system with open grated manhole cover that when everything is working correctly you can view the discharge.

RM

I do not believe either pump is VFD or soft start rated, this could be cause of winding failures. Yes under voltage can cause problems, but you state amps and volts were all good. Is pump controlled by contactor? Is there a coil that drops out when shut off? Could wiring be wrong? Single phasing cause loss of power and vibration. Verify contactor contacts are in good shape.

Pipes typically do not break without excitation. Impeller out of balance, pump not fully submerged, hydraulics not happy, single phasing....did you check for proper rotation?

Sorry still confused on your piping arrangement. You state broken pipe but you also state "up from the pump through the hose"? IF the "hose" has a hole in it, you no longer have 10' of TDH.

RM

Sorry it's been so long big factory to take care of. As I've stated before it's a pretty simple system when the waters down you can see the entire piping hose everything no leaks. As I also stated once part of the windings burnout that pump starts jumping around at the bottom of that pit like a cat on a hot roof and at that point the pump still pumps it doesn't have the force to evacuate the water at volume anymore. At this point we're just putting in a whole set of contactors timers and level controls. And take it from there. Also like I said before this thing ran for years problem free with all the same mechanical connections then burnout three pumps over a two-month period. Thank you for all your help

RM

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