Problem with Vertical Turbine Pump 1

[30432rc]

I have a project where we pump river water directly into a storage reservoir. Static Head (water elevation between reservoir and river) is 110m. The pump info is as follows:

Type of Pump: Open Lineshaft Vertical Turbine Pump
Rated Flow: 70 L/s
Rated TDH: 123m
Pump Efficiency @ Rated Flow: 82%
Motor HP: 150 HP, 600V, 3PH, 60Hz
Full Load AMPS: 133
# of pumps: 2
Soft Starters for both pumps

Problem:

The first day when we started the pumps, it was operating at or close to BEP. One of the pump is operating approximately 10 amps over the FLA and we quickly shut down the pump to prevent further motor damage. The other pump was operating below the FLA. Over time, the pump is losing flow and head (a suprise to us because BOTH units are decreasing). We're now operating the pump @ 44L/s @ 164 PSI.

We're currently investigating the problem and if some of the infomation presented above seem "fishy" Please provide your input.

Thanks!

 

[Artisi]

Your description is a little confusing - "we started the PUMPS - ONE of the pumps is operating 10 amps over FLA- we shut IT down - the pump is losing head - suprise to us because BOTH units are decreasing".

How many pumps are running at any one time?

Does the overloading pump run at the reduced capacity in overload condition?

1. Is the overloading pump running in the correct direction
2. Overloading pump - is the impeller setting correct maybe the impellers/s are rubbing on the casing?
3. Falling capacity - any sign of the inlet flow vortexing?4. how close together are the pumps?
5. are the pumps in a seperate "well" located in the river or inserted directly into the river.
6. any trash clogging the inlet screens (asume they have screens)
7. How accurate is your flow and pressure measurements.

 

[BigInch]

How are you operating at 44 l/s & 110 m now? Straight, valve pinched back, slower rpm?

http://virtualpipeline.spaces.msn.com

 

[TenPenny]

Some of the information is definitely fishy.

133 FLA on a 600 volt motor suggests to me that it's a 125 hp motor.


That said, you're running at 164 psi discharge, which is about 115 m head, which kind of makes sense with your 110 m static.

On startup, was the reservoir empty? If so, the initial static head would be lower, so the flow would be higher....now that the level in the reservoir is higher, the required head is higher, so your flow is lower.

Check your motor - are you sure it's not a 125 hp motor?

 

[30432rc]

Thanks Guys for replying so quickly, here are my response to the various questions:

How many pumps are running at any one time? One at the moment which is producing 44 L/s @ 160 PSI.

Does the overloading pump run at the reduced capacity in overload condition? No. We tested each pump independently and ONLY one pump ran over the FLA by about 10 AMPS.

1. Is the overloading pump running in the correct direction - YES
2. Overloading pump - is the impeller setting correct maybe the impellers/s are rubbing on the casing? - WILL CONFIRM
3. Falling capacity - any sign of the inlet flow vortexing? - NO VISIBLE SIGNS OF VORTEXING. WE HAVE APPROX. 2.8m - 3.3m OF SUBMERGENCE. TWO PUMPS ARE 1.5m APART CENTRE TO CENTRE.
4. how close together are the pumps? TWO PUMPS ARE 1.5m APART CENTRE TO CENTRE.
5. are the pumps in a seperate "well" located in the river or inserted directly into the river. - SEPERATE WELL
6. any trash clogging the inlet screens (asume they have screens) - CONFIRMED NO TRASH/DEBRIS FROM RIVER. WE HAVE 1/10" INTAKE SCREENS IN THE RIVER.
7. How accurate is your flow and pressure measurements. - CONFIRMED WITH CONTRACTOR AND INSTRUMENTATION ENGINEER THAT THE MAGNETIC FLOW METER AND PRESSURE TRANSMITTER ARE CALIBRATED. WE HAVE BOTH THE PRESSURE TRANSMITTER AND PRESSURE GAUGE ON THE SAME PUMP DISCHARGE HEADER AND THEY'RE BOTH READING THE SAME PRESSURE.

 

[BigInch]

1.5 m c/c sounds very very close.

http://virtualpipeline.spaces.msn.com

 

[Artisi]

A few more questions to try and get an idea of what might be happening;
1. From TenPenny - does the static head (level from river to water level in the reservour)increase as the reservour is filled or is it a fixed height for the delivery point?
2. What diameter is the "well"?
3. How does the water gain access to the "well"
4. If both pumps are identical and both installed and configured the same it is reasonable at this stage to assume that the o/loading unit probably has a mechanical or electrical problem not a hydraulic problem.

A dimensioned drawing showing the layout etc might also be helpful - you can post drawings by using the following link

http://www.freeimagehosting.net/

 

[JJPellin]

We have five cooling towers that use vertical turbine pumps. There are four pumps per tower ranging in size from 10,000 gpm to over 45,000 gpm. Vertical turbine pumps can be tricky. First, some of them have a horsepower curve that increases at low flow. So a pump that is running at low flow can be pulling normal amps that would otherwise suggest it is pumping a much higher rate. Within our population, we have three configurations of impellers. Some are open face impellers that are very sensitive to lift setting. Others have front and back wear rings with enclosed impellers that are much less sensitive to lift. Another group has closed impellers with radial wear rings, but also using lateral wear rings. At first glance at the drawing, these look like the second group. But that lateral wear ring makes the lift setting very important. The lateral rings are sometimes rubber coated. If the lift was set too tight and the impeller rubbed the ring, it could drag hard (high amps) until the rubber coating was worn away which would then cause a loss of pump performance. Depending on the length of the pump, the lift setting needs to allow for proper impeller clearance and shaft stretch.

Many of the things that could affect performance are already mentioned in the previous posts. A few others come to mind. We have some big vertical turbine pumps in water processing service that have a very unusual head design. Internal plugs inside the head can be removed or installed to provide discharge pressure at the mechanical seal or suction pressure at the seal. These pumps are installed in cans and have positive suction pressure above atmospheric. If the wrong plugs were left out, internal recirculation could drastically affect pump performance. Check a pump cross-section to look for any unusual configuration.

Suction conditions for vertical turbine pumps can be tricky. Sometimes they have a requirement for minimum submergence. Sometimes they have a requirement for Net Positive Suction Head. We have had cases where the project engineer only paid attention to the minimum submergence and installed pumps without adequate NPSH available. They cavitate all the time. Check both submergence and NPSH(r).

Sump design can be very important with these pumps. If the fluid is delivered to the pump suction with pre-rotation, the pump may cavitate severely even running close to BEP. There might be inlet screens to the pump sump and basket strainers attached directly on the pumps.

You didn't mention if the pumps are single stage or multi-stage. Are the impellers mounted using collets or are they keyed? An impeller could have come loose from its collet and be dragging extra horsepower, but not contributing to the flow.


Johnny Pellin

 

[30432rc]

To all who responded:

Thanks to all your responses! The pumps are now operating as per design and we found out the suction bell of the vertical turbine pumps were stuck with debris and tree roots. After we cleaned the wet well, everything was back to normal!

 

[Artisi]

Surprise - surprise

 

[BigInch]

Good work.

http://virtualpipeline.spaces.msn.com