OT- Submersible waste pump reversed.

g.mccormick

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We have two submersible waste pumps in a sump. Submittals for the pumps are 1hp, 1.5A@460VAC Motor, 91GPM, 50FT max.

Long story short, the motors were pulling over current and tripping the overloads after long running. The mechanical contractor (supplying contractor) had the pump supplier out. They closed down on a discharge ball valve to increase the discharge pressure and pull the pump backwards on the curve, dropping the motor power. Now, we have issues with the pumps not keeping up, and although we have no way to measure it definitely, it feels like the pumps are not providing the gpm that they should. I have asked about rotation to which the contractor stated it was checked and is correct.

I know that a centrifugal pump running in reverse will still provide some flow albeit much lower performance. Is there any chance that it would also increase current consumption?
 
I've seen reverse running Flygt pumps pull high amps. But also low amps due to less work done. I think it depends a bit on the impellor style.

I'd want to check the rotation again. There should be an arrow on the volute somewhere. Pull it up, give it a quick on-off flick and then check direction.

Or just reverse direction and see what happens. I prefer the visual inspection.

Is it possible to stop flow into the chamber? You could then did a timed draw down test and calculate the average flow.

Screwing down the discharge valves is a terrible solution to a pump that has been incorrectly sized. They're essentially modifying the system curve and adding more friction loss, so you will be wasting energy.
 
I concur with Saffa, we had a Grundfos centrifugal submersible (not a long pipe fitting type) pump that pulled 2x FLC when running in reverse and was pumping a full pipe (there was only about 2M of head)
Also just to confuse things the Grundfos direction arrow is impeller direction and not kick, so the direction arrow tells nothing you can see, so it needs to be the opposite to equal the kick.
 
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I would check with the pump maker to make sure it is okay to run in reverse without damage before attempting to do that as a test. Some pumps are fine with it, others not so much. But if they give the thumbs up, that is certainly simpler that pulling a chit covered pump out of a sump and bumping it.
 
Like OkiePC implies I have had pumps screw apart and destroy themselves if run in reverse.


Pumps and motor current can be unusual to figure out. I have a customer that has a low pressure warning on a sprat wash line, but not using any pressure switch. If the pump is giving a good pressure the motor amps drop to a nice level. If the pressure increases there will be an increase of motor amps as expected - but if the pressure DECREASES because of a broken fitting, too many missing spray nozzles, or anything and the motor seems like it should them run easier and draw less current it actually pulls more current doing less work. They don't know why, just their alarm works.
 
Thanks all. I knew already that I wanted to get the contractor to pull the pump and let me visual see the correct rotation, I just wanted another ear on in. Luckily this is industrial waste in a clean building (think air handler condensate drains, cooling tower blow-down, etc) so there should not be any turds on it (unless a ****ed off contractor has had his way with it).
 
OkiePC said:
... Some pumps are fine with it, others not so much. ...
Click to expand...
Learned that lesson the hard way. Spun the king nut off the end of a deep well turbine once, dropped the bowls to the bottom of the well. Cost me about $15,000 to pull the pump, fish the bowls out, repair it all and put it back in. Ever since then I learned to bump-check the pump rotation on the surface.
o_O
 
jraef said:
Learned that lesson the hard way. Spun the king nut off the end of a deep well turbine once, dropped the bowls to the bottom of the well. Cost me about $15,000 to pull the pump, fish the bowls out, repair it all and put it back in. Ever since then I learned to bump-check the pump rotation on the surface.
o_O
Click to expand...

ouch!
 
1) Do you have a pressure gauge on the pump discharge, upstream of the throttled all valve? If so measure the pressure.

2) Is the pump submerged in a wet well? If so do a draw down test by measuring level change and time.

3) Measure the power draw, or calculate it from the volts and amps and motor data sheet.

4) Compare the results to the pump curve. The measured data should be within about 5% or 10% of the curve data.
 
jraef said:
Learned that lesson the hard way. Spun the king nut off the end of a deep well turbine once, dropped the bowls to the bottom of the well. Cost me about $15,000 to pull the pump, fish the bowls out, repair it all and put it back in. Ever since then I learned to bump-check the pump rotation on the surface.
o_O
Click to expand...

I worked at a water utility out west that had some deep wells, some were submersible, some had vertically mounted motors (All were 5kv). Most of them had an "anti-back spin" feature, either something like a sprague clutch for the above ground motors to prevent ~700 feet of shaft from spinning apart, and the submersibles were rotation checked before going down hole. Those bowls would indeed come off, and the well crew would kill you. Or the electric shop would have to buy them lunch.
 
My experience with submersible pumps is limited to the typical big players in the industry here in NZ which is Grundfos, Sulzer and Flygt.

Can't say I've ever had any impellors fall off from reverse running. In fact we have a few stations where the drives are set up for a blockage removal function which spins them forward and reverse a few times if the motor torque gets too high, to spit out the rags.

But certainly checking with the manufacturer won't hurt if you're unsure.

Toms approach is the most scientific and I wish more of our clients would design their valve chambers (for wastewater pumping stations) with a 1/2" ball valve already fitted on the rising main, and enough straight pipe exposed for a flow meter!
 
g.mccormick said:
We have two submersible waste pumps in a sump. Submittals for the pumps are 1hp, 1.5A@460VAC Motor, 91GPM, 50FT max.

Long story short, the motors were pulling over current and tripping the overloads after long running. The mechanical contractor (supplying contractor) had the pump supplier out. They closed down on a discharge ball valve to increase the discharge pressure and pull the pump backwards on the curve, dropping the motor power. Now, we have issues with the pumps not keeping up, and although we have no way to measure it definitely, it feels like the pumps are not providing the gpm that they should. I have asked about rotation to which the contractor stated it was checked and is correct.

I know that a centrifugal pump running in reverse will still provide some flow albeit much lower performance. Is there any chance that it would also increase current consumption?
Click to expand...

It sounds like the motor/pump combination you're using isn't correct. The lower the head pressure, the higher the flow. Increased flow, increases motor amperage. Choking the discharge down, reduces the amperage, but also lowers the discharge GPM.

It sounds like you need to install bigger pumps rated for the head pressure you have and GPM you need.
 
Keep in mind that the flow the pumps "should" provide may no match the flow you want them to. What they should provide is established by the pump curve, as Cow says. Without pressure and flow readings you are just guessing.

You could try incrementally opening the ball valve until you start closing in on the max amps. That will max your flow. Just make sure that as wet well level and discharge head changes you don't go into overload.

As an aside, I dislike throttling wastewater pumps. It is a good way to find out how many rags and sanitary wipes your citizens are flushing down their toilets!
 
Well I finally got them to pull the pumps and let me look. Both rotating backwards. I swapped a few wires around, and they reinstalled them by lowering on chains, but they need someone to go down and check alignment with rail adapter as I think they are leaking a bunch. So hopefully tomorrow when they bring in the winch we can re-check pump test. Thanks all.
 
Glad to hear they are still running, albeit backwards.
How were the faces of the contractor after telling you they were running in the right direction?
 

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