Two pumps connected in parallel runs continuously

[Julian]

Hello everyone, I'm a Plumber/ pump man from the Philippines. I need advice regarding pump problem. I dont know if this the right forum, but here it is. Two pumps connected in parallel runs continuously. What puzzled me is that whenever I partially closed main discharge valve or any of the discharge valve of both pump the pressure drops. Now this my first encounter with such a pump. Please refer to attached files. Is it perhaps a variable speed/ discharge pump that reacts to the pressure transmitter installed at the discharge. Pump is servicing a four story building. pressure is 70 psi drops to 50 to 60 whenever I partially close any discharge valve. Looking forward to your advice.

 

[quality]

Hello everyone, I'm a Plumber/ pump man from the Philippines. I need advice regarding pump problem. I dont know if this the right forum, but here it is. Two pumps connected in parallel runs continuously. What puzzled me is that whenever I partially closed main discharge valve or any of the discharge valve of both pump the pressure drops. Now this my first encounter with such a pump. Please refer to attached files. Is it perhaps a variable speed/ discharge pump that reacts to the pressure transmitter installed at the discharge. Pump is servicing a four story building. pressure is 70 psi drops to 50 to 60 whenever I partially close any discharge valve. Looking forward to your advice.

Ive not read all the replies but this must be a chiller or cooling type Of

 

[Julian]

Ive not read all the replies but this must be a chiller or cooling type Of

Its the water supply pump for a hotel.

 

[quality]

Its the water supply pump for a hotel.

ok .

 

[rpm]

Been a long time but if my maths is correct that is around 200 ft head.
Plus earlier you said closing valves showed a reduction in pressure on the gauge now it raises.

 

[John.g]

There certainly seems to be the facility for VSD as the Grundfos controller has a SP and PV but both switches VSD 1 and VSD 2 appear to be in the off position so assume that pumps are running in fixed (full) speed mode then if pump 1 not doing anything and NRV not working then shutting valve 1 will certainly increase the system pressure but does not explain the puzzle as to the pressure decreasing when the main discharge valve is throttled in?, maybe worth repeating this test. Also that 83 psi, (57 M) would seem to point to a 60 HZ supply as the maximum no flow head running at 50 hz is 41 M. (see pump curve, post #34. and compare with pump name plate in post #1) and also is borne out in practice as head is proportional to speed squared, hence 41*(60/50)^2 = 59 M (no flow head)

 

[quality]

The pump curve is irrelevant if the 1 pump is against the other

 

[John.g]

Not sure what you mean by the above but one other thing Julian could check is to shut valve 1 fully and see if the motor stops turning after a minute or so as it may not be switched on and is just turning in reverse because of a defective NRV.

Any ideas on why 50 hz motors are coupled to 3600 RPM pumps as 50 hz motors should not be fitted in countries that have a 60 hz electrical supply, if this is the case.?

 

[Julian]

Been a long time but if my maths is correct that is around 200 ft head.
Plus earlier you said closing valves showed a reduction in pressure on the gauge now it raises.

Yeah my bad. I have corrected this twice already. I think I must correct also the original post.
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Not sure what you mean by the above but one other thing Julian could check is to shut valve 1 fully and see if the motor stops turning after a minute or so as it may not be switched on and is just turning in reverse because of a defective NRV.

Any ideas on why 50 hz motors are coupled to 3600 RPM pumps as 50 hz motors should not be fitted in countries that have a 60 hz electrical supply, if this is the case.?

Yes this also comes to mind, I will definitely check this. Even at first visit I have already doubts that pump 1 is not running I have check repeatedly if its turning.
I don't have the slightest idea why this is so. manager said that 1 pump is already replaced with new, by a contractor from grundfos. I ask her why she did not call them for this. She just make faces and tell me that they don't like the fact that grundfos refer them to the contractor.
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Is there a possibility to edit post one. So that new comers to this discussion won't be confused by my mistake.

 

[John.g]

Yeah my bad. I have corrected this twice already. I think I must correct also the original post.
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Yes this also comes to mind, I will definitely check this. Even at first visit I have already doubts that pump 1 is not running I have check repeatedly if its turning.
I don't have the slightest idea why this is so. manager said that 1 pump is already replaced with new, by a contractor from grundfos. I ask her why she did not call them for this. She just make faces and tell me that they don't like the fact that grundfos refer them to the contractor.
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Is there a possibility to edit post one. So that new comers to this discussion won't be confused by my mistake.

Re your corrected statement..... just to be quite clear again, you are stating that opening valve 1 results in reduced pressure and shutting the main discharge results in reduced pressure??

Check with your clamp ampmeter if the No1 pump is drawing power, if so, check direction of rotation which, if reversed will still pump but at much reduced head (~50%) and flow rate. It then only requires two phase change to get correct rotation.
If you havn't got your ampmeter carry out the (pump 1) closed valve test and see if pump stops.

 

[snowhead]

That control box has 2 Variable Speed Drives in it.
1 is the Schneider at the top, showing 60 which could mean it's being driven at full speed, 60hz (the frequency in the Phillipines) or may just be showing the incoming frequency, it depends which parameter the display is set to show.
The other is the Grundfos.
Whether they were the same and 1 has been replaced I don't know.
They control speed from pressure and can do Duty / Standby changeover, depending how they are set up.

The Grundfos at the bottom is in fault, O. P,, Over pressure.
This may need resetting, depending whether the parameters are set to turn of the pump in fault or leave it running.
As there is only 1 pressure sensor, only 1 VSD can have a Pressure input.
However they will most likely be linked so when 1 fails the other takes over

I've found links to the manuals to both VSD

To check if either or both pumps are running you should be able to see the Fan on the top end of the motor running.
If one pump is not being powered but is being driven by the flow from the other pump passing through the NRV, then it will be running slower.

The 2 switches at the top will be to bypass the VSDs if they fail.

 

[Julian]

Re your corrected statement... just to be quite clear again, you are stating that opening valve 1 results in reduced pressure and shutting the main discharge results in reduced pressure??

Yes, this is correct

Check with your clamp ampmeter if the No1 pump is drawing power, if so, check direction of rotation which, if reversed will still pump but at much reduced head (~50%) and flow rate. It then only requires two phase change to get correct rotation.
If you havn't got your ampmeter carry out the (pump 1) closed valve test and see if pump stops.

I will go back with my ampmeter and check power draw. direction of rotation and fully close valve 1 test and also the main valve partially close test.
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That control box has 2 Variable Speed Drives in it.
1 is the Schneider at the top, showing 60 which could mean it's being driven at full speed, 60hz (the frequency in the Phillipines) or may just be showing the incoming frequency, it depends which parameter the display is set to show.
The other is the Grundfos.
Whether they were the same and 1 has been replaced I don't know.
They control speed from pressure and can do Duty / Standby changeover, depending how they are set up.

The Grundfos at the bottom is in fault, O. P,, Over pressure.
This may need resetting, depending whether the parameters are set to turn of the pump in fault or leave it running.
As there is only 1 pressure sensor, only 1 VSD can have a Pressure input.
However they will most likely be linked so when 1 fails the other takes over

I've found links to the manuals to both VSD

To check if either or both pumps are running you should be able to see the Fan on the top end of the motor running.
If one pump is not being powered but is being driven by the flow from the other pump passing through the NRV, then it will be running slower.

The 2 switches at the top will be to bypass the VSDs if they fail.

Can you please post links of the manuals. for both VSD's.
My guts tells me that pump 1 is running slower.
what does SP and PV stands for?
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How do I switch off pump 1 or pump 2. In case I need to?
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Thanks for staying with me guys. I've confidence now I can solve this, I mean we can 🙂

 

[rpm]

Thanks for staying with me guys. I've confidence now I can solve this, I mean we can 🙂

It`s certainly more interesting than the average plumbing post Julian.

 

[John.g]

I will go back with my ampmeter and check power draw. direction of rotation and fully close valve 1 test and also the main valve partially close test.
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Can you please post links of the manuals. for both VSD's.
My guts tells me that pump 1 is running slower.
what does SP and PV stands for?
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How do I switch off pump 1 or pump 2. In case I need to?
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Thanks for staying with me guys. I've confidence now I can solve this, I mean we can 🙂

Its certainly very interesting , SP probably stands for Set point and PV for Process value, I would be doubtful if the controllers were designed to maintain a given variable speed, generally the SP would be a desired manifold pressure ( or in the case of a very tall building may have the pressure transducer located near the top) and the variable speed controller would then modulate the variable speed output to maintain this constant pressure which would possibly be ~ 50 psi.
I had a lot of experience with a mixture of fixed speed combined with VSD on cooling tower circulating pumps and I can definitely say that if the VSD, for whatever reason, ramped down so much that its head was much lower than the fixed speed pump then the NRV would shut to stop reverse flow through the pump, so obviously if the NRV on your pump 1 is defective and the pump is running at a much lower speed then its quite possible to get reverse flow through that pump. Its also possible, however unlikely, that this pump is running at full speed in the wrong direction which will give a much reduced head to give this reverse flow. Your tests on this pump will solve that mystery easily enough.
The big mystery for me is as to why the manifold pressure reduces when the main discharge valve is throttled in but again you are going to carry out a confirmation test on this.

 

[quality]

Not sure what you mean by the above but one other thing Julian could check is to shut valve 1 fully and see if the motor stops turning after a minute or so as it may not be switched on and is just turning in reverse because of a defective NRV.

Any ideas on why 50 hz motors are coupled to 3600 RPM pumps as 50 hz motors should not be fitted in countries that have a 60 hz electrical supply, if this is the case.?

1440 ish at nominal voltage

 

[John.g]

what does 1440 refer to?

 

[snowhead]

Manual for the drive Labelled Grundfos, I suspect Grundfos had these rebadged with their name;

http://www.rhymebus.com.tw/files_web/RM6%20series(9426).pdf

Manual for Schneider drive;

https://inverterdrive.com/file/Schneider-Altivar-ATV212-Installation

 

[Julian]

Its certainly very interesting , SP probably stands for Set point and PV for Process value, I would be doubtful if the controllers were designed to maintain a given variable speed, generally the SP would be a desired manifold pressure ( or in the case of a very tall building may have the pressure transducer located near the top) and the variable speed controller would then modulate the variable speed output to maintain this constant pressure which would possibly be ~ 50 psi.
I had a lot of experience with a mixture of fixed speed combined with VSD on cooling tower circulating pumps and I can definitely say that if the VSD, for whatever reason, ramped down so much that its head was much lower than the fixed speed pump then the NRV would shut to stop reverse flow through the pump, so obviously if the NRV on your pump 1 is defective and the pump is running at a much lower speed then its quite possible to get reverse flow through that pump. Its also possible, however unlikely, that this pump is running at full speed in the wrong direction which will give a much reduced head to give this reverse flow. Your tests on this pump will solve that mystery easily enough.
The big mystery for me is as to why the manifold pressure reduces when the main discharge valve is throttled in but again you are going to carry out a confirmation test on this.

"The big mystery for me is as to why the manifold pressure reduces when the main discharge valve is throttled in but again you are going to carry out a confirmation test on this."

this is the thing that make me doubt if I lose my head momentarily🙂
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Manual for the drive Labelled Grundfos, I suspect Grundfos had these rebadged with their name;

http://www.rhymebus.com.tw/files_web/RM6%20series(9426).pdf

Manual for Schneider drive;

https://inverterdrive.com/file/Schneider-Altivar-ATV212-Installation

Thanks snow, I downloaded it for learning.

 

[Julian]

It`s certainly more interesting than the average plumbing post Julian.

I'm glad that you find this interesting. And when we get to solve this... I sincerely wish I can buy you all some beer/whisky... for a lil celebration 🙂🙂.
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I have little knowledge with motors, so I'd like to throw this question out there. If a 50hz motor run on 60 hz, is it going to run at 20% more speed than its designed to run at.
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Ok, so we, me and my son, did the test. Pressure at 70 psi to start with. first test was the direction of rotation test. I did a simple poke test with a twist tie at the back of the motor. The twist tie bent to the direction of rotation when it hits the fan blade. we did the test at least 3 times for each pump and found out that pumps are running in opposite directions. Second test. Valve 1 full close test. Pump 1 stop spinning as soon as valve is full close. pressure is around 85psi. Did the test 2 more times. each time the pump stop turning as soon as the valve is fully closed. But it takes time for pressure to go down to 70 even when valve 1 is already full open. I Cancelled the ampere test as motor 1 is clearly not operating. So we have already the "broken NRV 1" confirmed. Proceeded to main valve fully closed test. pressure at 70 psi. pressure does not change but motor 1 appeared to be running faster. closed valve 1 slowly pressure increase to around 80. repeat the same test and got same result. All throughout did not hear the motor changing speed.
Motor 1 nameplate says 60hz and is connected to dunfoss VSD. Motor 2 nameplate says 50hz and is connected to schnieder VSD. Pump 1 appear to have previous leaking as there is dry mud all over. see photo.
So yeah I've lost my mind for a moment on the main valve test. Maybe because I was alone and have to go up and down the ladder to close the valve little by little and look at the pressure gauge. by chance the pressure drops courtesy of valve one, at the precise moment when main valve is almost closed. Yes it took time for pressure to drop after opening the valve 1. Its because the pump has to gain momentum going to the opposite direction.
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MY course of action plan. First is to study the manuals of VSD's. Get a new NRV and replace NRV1. Test pump one if ok. If ok put it as the lead drive and reprogram the whole thing to operate at constant pressure. If pump one is broken but motor is ok, interchanged pumps and motors and put 60hz motor and good pump in service. Overhaul broken pump and attached to 50 hz motor as backup.
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[rpm]

Re pump 1 leakage, that will be the mechanical seal in the top housing, the top of it can be seen if you remove the coupling guard but the bad news is it is a complete strip down of the pump to replace it. Could this be the reason pump 1 has been taken out of operation? Unless you have experiance and the tool I wouldn`t recommend you attempt the rebuild tbh.

 

[snowhead]

http://hydro-tech.com.my/wp-content/uploads/woocommerce_uploads/2019/06/Compact-R-Brochure.pdf
50hz, but the basic system will be the same.

Info on CR pumps

http://daparak.com/wp-content/uploads/2013/11/CR-CRI-CRN-CRT-Installation-Operations.pdf