Electric Water Pump has slowed Down

[ElectroEnthusiast]

We have an Water Pump rated 0.25HP which used to normally pump water from ground tank to supply tank in 45 min i.e., it would pump 3000 lts(estimated) of water in 45 min. The pump got spoilt and was repaired few times. From what i remember, the capacitor was changed once and the other time the internal motor winding was rewound.

My question is, 1) What made the pump to slow down?
2) Will there be any change in power consumption of motor?
3) Has the efficiency of motor decreased?

 

[BradtheRad]

Not knowing if it's a submersible or ground-level pump...

1.

Is the water clean or murky? If the pump is a positive displacement type, then it may be the kind that cannot tolerate any dirt getting inside the cylinder. I don't know that this was the same as your problem.

Or... did water get at the bearings? It's a remote chance. Of course we would expect it to be designed to bear up in a normal installation.

Did it ever run dry? If there are no safeguards then it might allow the motor to run fast and overheat the bearings. Afterwards it would never act right.

2.

When a motor winding goes bad, it's a good bet that it carried overmuch current and overheated.

Did it ever blow a fuse or trip a breaker?

Did the system ever reach an abnormally high pressure? That would make a pump work harder, since it must overcome the high pressure.

3.

If you could monitor its power draw then you would be able to notice a change.

Are you sure it's not running too hard and too long? For 1/4 HP to pump 3000 liters in 45 min... suggests it is sending 1 liter a second.

Unless it's designed to run continuously, a motor needs to cool down after operating for so long. Its rated duty cycle says it can be on for so many minutes at so much current, then off. To operate it longer than that, or harder, is risky.

 

[kripacharya]

We have an Water Pump rated 0.25HP which used to normally pump water from ground tank to supply tank in 45 min i.e., it would pump 3000 lts(estimated) of water in 45 min. The pump got spoilt and was repaired few times. From what i remember, the capacitor was changed once and the other time the internal motor winding was rewound.

My question is, 1) What made the pump to slow down?
2) Will there be any change in power consumption of motor?
3) Has the efficiency of motor decreased?

Pump slowing down will happen if there is a variation in the power supply voltages, OR there is excessive load on the motor due possibly to build-up of dirt/ any other reason for increase in the pressure head. In addition it is not advised to run such motors "dry" - which is a bit counter-intuitive but apparently common knowledge. I suspect there is no controller on your pump, and that it often runs dry in an effort to ensure your overhead tank is full.

In addition - the heavier load could be caused if your overhead tank has a float valve which shuts off when its full, and hence dramatically increases the load on your motor.

The solution to all of these is to install an automatic pump controller. Its an initial expense but leads to many trouble-free months/ years of hands free operation. Make sure if you get one of these that it also has a detector for lower tank empty condition.

Rewinding is a cheaper option than buying a new motor, but once again too often the rewinding is below spec, for exactly this reason. This implies less than original power output and probably higher current draw.

 

[ALERTLINKS]

What if they wound with aluminium wire, instead of copper enamel wire. The capacitor may be weak again.

 

[chuckey]

I have never heard of ali coil winding wire.Ali wire is rubbish. I lurk on some American sites and in the 70s and 80s they used a lot of Ali in power cabling, its all failing now and will be all be replaced within 20 years. With out further data on the motor and pump type I can not say more. The capacitor is mainly used for starting the motor in the correct direction. i.e. without the cap It won't start.
Frank

 

[ALERTLINKS]

**broken link removed**

https://www.alibaba.com/trade/search?fsb=y&IndexArea=&CatId=&SearchText=al+enamel+wire
Here in PK your motor will always be rewound with this type of copper looking aluminium wire. It is coloured so as keen people are easily misled.
Don't capacitor also add some torque to motor?

 

[chuckey]

Yes it does. Can you measure the running current of the motor and compare it with the name plate ratings? Is the foot filter blocked? is it sucking in air below the pump? is there a leak above the pump or a blockage?
Frank

 

[ElectroEnthusiast]

The pump looks similar to this:

I shall make a note of its power consumption in some time. I think it is a positive displacement pump(not sure)? How can i know the type of the pump or mechanism it uses? The pump is at the ground level, it pumps water from a underground tank to a tank 2 floors above.

 

[kripacharya]

read my post#3 above. It explains the answer to exactly whats concerning you about the pump

 

[ElectroEnthusiast]

Not knowing if it's a submersible or ground-level pump...

1.

Is the water clean or murky? If the pump is a positive displacement type, then it may be the kind that cannot tolerate any dirt getting inside the cylinder. I don't know that this was the same as your problem.

Water is nearly clean.

Or... did water get at the bearings? It's a remote chance. Of course we would expect it to be designed to bear up in a normal installation.

No, but how does water getting into bearing affect?

Did it ever run dry? If there are no safeguards then it might allow the motor to run fast and overheat the bearings. Afterwards it would never act right.

Not Dry run, the motor requires watering(i'm not getting the technical word) after every dry run.

2.

When a motor winding goes bad, it's a good bet that it carried overmuch current and overheated.

Did it ever blow a fuse or trip a breaker?

No, it never blowed the fuse, but i suspect once when the winding was gone, we had a trip.

Did the system ever reach an abnormally high pressure? That would make a pump work harder, since it must overcome the high pressure.

What high pressure? i'm not getting you. Please can you elaborate?

Pump slowing down will happen if there is a variation in the power supply voltages, OR there is excessive load on the motor due possibly to build-up of dirt/ any other reason for increase in the pressure head. In addition it is not advised to run such motors "dry" - which is a bit counter-intuitive but apparently common knowledge. I suspect there is no controller on your pump, and that it often runs dry in an effort to ensure your overhead tank is full.

We raised the tank to 10 ft a few years ago, will that be the reason for increase in load? But, initial years, it worked well. I still suspect low quality winding.

Rewinding is a cheaper option than buying a new motor, but once again too often the rewinding is below spec, for exactly this reason. This implies less than original power output and probably higher current draw.

I still have a question, what affected motors speed/efficiency? Did that happened because of poor-quality repair (including winding and capacitor change).

Also, please tell me why a capacitor is required? How can i know the pinnacle upto which the motor can pump the water?

 

[chuckey]

That pump is a suction pump, as its sucking water up. Any air leak on the inlet line will totally destroy its performance. Likewise it should have a foot valve to maintain ther water in the inlet line. I suspect that the pump bore is worn out and needs fixing. New seals /rings at a minimum, perhaps the actual bore needs machining. What you should do is to break the inlet line and measure the vacuum on it to test this. The OEM will list this in its data sheet.
Frank

 

[BradtheRad]

Everything points to a pump that is worked too hard. It might be due to:
* too high/heavy a column of water being lifted
* pump lacks adequate power
* overmuch pressure in the system
* low supply voltage

I believe you need the safeguards mentioned by Kripacharya in post #3.

No, but how does water getting into bearing affect?

The bearings must never lose lubrication. If this happens then they are liable to break down. I don't know that this is the case, it was only an idea to consider. Bad bearings usually cause noisy operation, so if the pump does not squeak or clatter, etc., then the bearings are probably good.

Not Dry run, the motor requires watering(i'm not getting the technical word) after every dry run.

Yes, the pump must be primed after it is allowed to go dry. It does not sound as though this happens often. You don't say you need to prime the pump often.

What high pressure? i'm not getting you. Please can you elaborate?

There should be a sensor which detects either water level or water pressure. The sensor tells the pump to turn off and on. If the sensor gets out of adjustment then the pump might continue to run and build up overly high pressure in the system.

Is there a pressure gauge attached to the tank? Normal pressure varies between 20 and 50 pounds/sq.in. Since your pump is having problems I would not set it for more than 40.

We raised the tank to 10 ft a few years ago, will that be the reason for increase in load? But, initial years, it worked well. I still suspect low quality winding.

An increase in 10 feet is not too much, as long as it is still within the pump's lifting spec.

Since you say the pump worked well after it was repaired, it suggests the windings should be okay, as long as the pump is not overburdened.

If at any time the pump started to run slow, then it would cause the current to increase. This can burn up windings.

Reasons for the pump to run slow:
* If the supply voltage were to drop
* If the load were to increase

I still have a question, what affected motors speed/efficiency? Did that happened because of poor-quality repair (including winding and capacitor change).

Motors are complicated. It is not easy for us to determine how to match the motor to the load, and for what length of running time. The label should state the manufacturer's specs (but it would not be surprising if the label information is incomplete).

If there was just one incident where the motor overheated, or smoked, or stopped while it was powered up, then its performance would have suffered.

Have you touched the motor after it runs for 40 minutes? Is it hot? If so then you should somehow reduce its running time to 20 minutes, or 10 minutes. Then let it cool down before you run it again.

Also, please tell me why a capacitor is required? How can i know the pinnacle upto which the motor can pump the water?

The capacitor may be for power factor correction. I don't know whether its value should be different at slower pump speeds.

The height that the pump can lift water is determined by the power capability of the motor, and the robustness of the pump innards. The label should state specs. However when a pump has been overworked, it is no longer likely to meet those specs.

 

[ElectroEnthusiast]

thanks kripacharya, chuckey and Brad

There should be a sensor which detects either water level or water pressure. The sensor tells the pump to turn off and on. If the sensor gets out of adjustment then the pump might continue to run and build up overly high pressure in the system.

Is there a pressure gauge attached to the tank? Normal pressure varies between 20 and 50 pounds/sq.in. Since your pump is having problems I would not set it for more than 40.

How will the tank pressure effect? the pipe is not over head tank has no immersed water pipe. Please give me a link to read about this.

I'll check for the hotness of the pump; sound and exact time it takes to complete one cycle of filling the tank. I'll also check for sound from the bearings and for any air leaks in near the motor. I'll also try to measure the voltage at the nearby receptacle.

One thing i forgot to mention, the motor is connected to an invertor/UPS. Might that have affected anything? But, we usually use motor only on mains supply. When there's an power cut, we switch off the motor(since it overloads UPS).

 

[BradtheRad]

How will the tank pressure effect? the pipe is not over head tank has no immersed water pipe. Please give me a link to read about this.

The pump must overcome (a) the weight of the column of water in the pipes, and (b) the pressure in the system.
If these are too great, they will slow down the pump, and cause overmuch current in the windings.

At this time it is essential that you find out what is the pressure in the system. Can you look at all the plumbing in the house, and find a gauge attached anywhere?

Or there ought to be a threaded fitting, on the pump or tank, into which you can install a gauge. The diameter and threads-per-inch must match. The fitting is capped, therefore you must first drain water until there is no pressure, then remove the cap, and install the gauge.

If you cannot obtain or install a gauge, then you need the help of someone who is experienced with plumbing. He may temporarily attach a gauge to a faucet, to find out what is the low and high range of system pressure. Or else he may get a rough idea of the pressure by putting his thumb over a running faucet, to stop the water flow.

You need to make the pump's job easy. In my estimation it should stop when pressure reaches 35 or 40 psi.
It should turn on when pressure is down to 20 or 25 psi. However if fixtures do not operate properly in that range, then you may have no choice except to adjust pressure upward.

I'll check for the hotness of the pump; sound and exact time it takes to complete one cycle of filling the tank. I'll also check for sound from the bearings and for any air leaks in near the motor. I'll also try to measure the voltage at the nearby receptacle.

Yes. You need to measure voltage at the pump when it is running. At the beginning of its operation, and at the end. If voltage goes below the specified figure, then the pump will run slow, and draw overmuch current.

One thing i forgot to mention, the motor is connected to an invertor/UPS. Might that have affected anything? But, we usually use motor only on mains supply. When there's an power cut, we switch off the motor(since it overloads UPS).

The UPS should let mains power go to appliances unchanged. However if there is a bad connection anywhere in the UPS, it will cause a voltage drop.

If there is a drop in AC V at the pump, it will try to compensate by drawing more current.
For example, if supply voltage goes down 20 percent, then current goes up 20 percent. This starts to overheat the windings, and if it gets bad enough it will cause motor breakdown.