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.

 

[John.g]

Thanks everyone for helping out. This one really puzzle me. I'm a guy who messes with everything and I can normally find my answers on my own. This is one of the few cases where I have to ask help so thank you.

Thanks Jhon, there are NR's on the suction side of the pumps, so I dont think reverse rotation can/will occur. The nameplates I publish is one for the pump and one for the motor. Motor and pumps are of the same model. I mean pump 1 and pump and motor 1 and motor2 is the same.

Thanks but the motor nameplate(s) suggest 50 hz and the pump rating is based on 60 hz, can you say where these pumps are installed and the max running speed/pump curves can then be established.
Have to considered shutting the main discharge valve fully, very briefly, and the indicated pressure will then tell alot. You could also, again very briefly, shut each pump discharge valve fully and note the pressures in both cases.
The 30 gall. pressure (expansion vessel?) will probably act as a buffer/accumulator to give a steady pressure if pumps are variable speed controlled and if stop/start will reduce the frequency.

 

[Danb]

I imagine the nrv will be the type with a simple flap design.
I've seen the paddle flap damaged and corroded

 

[Chuck]

What puzzled me is that whenever I partially closed main discharge valve or any of the discharge valve of both pump the pressure drops.

I might be missing something, but assuming the pump(s) are on either their P1 or P2 curves that's how they are intended to operate. They reduce their outlet pressure when the flow is reduced. This is usually an energy saving measure. The spec for the pump is here:

CR 10-4 A-A-A-E-HQQE

Vertical, multistage centrifugal pump with suction and discharge ports on the same level. The pump head and base are in cast iron - all other wetted parts are in stainless steel (EN 1.4301)

product-selection.grundfos.com

 

[John.g]

Excellent observation Chuck, smart pumps with proportional pressure (PP) control, so in maybe answering Julian's original question, the highest pressure is obtained by throttling one pump until the other reaches its max speed but the most economical way should be to run with both pumps unthrottled but this will give the lowest pressure and may not satisfy all the hotel guests but will also give the greatest redundancy in the event of any pump failure, the guy who set it up probably knew what he was doing.

 

[Julian]

Post the model number of the whole pump set, not the numbers of the pump or motor that you have posted already.
Post a picture of the front of the control box.
If it was variable, you would hear the speed of the motors increasing and decreasing as the system pressure varied and the pumps tried to match it.
There would either be an inverter box on the side of each motor of within the control box.
There would most likley be a display on the front of the box showing the speed.

Thanks, I will take more photos and do I you said.
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Stab in the dark - Is motor rotation correct and inlets & outlets of the pump the right way round?

Why put NRV on inlet side?

Your stab is interesting. I'm sure at least one pump (pump 2) is working well because pressure is 70 psi. There could be something wrong with pump 1. I will also check for this.
The pump is drawing water from below. installing NRV on the discharge side will cause draining of water from the suction side when pump is on standby. Oh yeah, I remember there should be a foot valve on the cistern. added to check list.
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I might be missing something, but assuming the pump(s) are on either their P1 or P2 curves that's how they are intended to operate. They reduce their outlet pressure when the flow is reduced. This is usually an energy saving measure. The spec for the pump is here:

CR 10-4 A-A-A-E-HQQE

Vertical, multistage centrifugal pump with suction and discharge ports on the same level. The pump head and base are in cast iron - all other wetted parts are in stainless steel (EN 1.4301)

product-selection.grundfos.com

Thanks Chuck. If this is the case there should be a flow sensor. I did not see one. But I will check again.

 

[Julian]

"What puzzled me is that whenever I partially closed main discharge valve or any of the discharge valve of both pump the pressure drops".

Assuming both pumps running then yes shutting in valve 1 should increase the pressure reading on this pump but the pressure read by pump 2 should decrease as this is effectively reading system pressure.
If you are running at 60 HZ then a fully closed valve should give ~ 85 psi, if running on 50 HZ then the closed valve pressure should be 58.5 psi assuming full speed in both cases, as you mentioned 70 psi above then it looks like a 60 hz frequency or else pressure gauges are faulty.

I'd like to stress that there is only one pressure gauge for the whole system. Please refer to the drawing I made.
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The pumps may take breaks as well once pressure is stable.
Soon as a tap or showers run pumps kicks in on pressure drop.
Hotels are great bet there's leaks and cisterns overflowing into pans all over the place. Pumps I should think will end up running all the time

Yep, leaks is one thing I am considering also. And if its high up will cause siphoning.
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Bleed valves are just under the motor & pump shafts coupling. These rarely suffer from trapped air due to the mulitstage design.
Very wise to be cautious untill you fully understand the pumps and the installation, if in doubt then walk away.

"if in doubt then walk away." yep that I will do. But hey this is the first time I encountered such a system with such a problem. An opportunity to learn and of course the excitement. I am not very good at control systems. But I was able to design and built a control system for a remote controlled gate I have constructed. I design and built the whole thing with a friend. Still running after two years. But looking at the control board of this pump system... I will need help with this also, i'm sure.
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Thanks but the motor nameplate(s) suggest 50 hz and the pump rating is based on 60 hz, can you say where these pumps are installed and the max running speed/pump curves can then be established.
Have to considered shutting the main discharge valve fully, very briefly, and the indicated pressure will then tell alot. You could also, again very briefly, shut each pump discharge valve fully and note the pressures in both cases.
The 30 gall. pressure (expansion vessel?) will probably act as a buffer/accumulator to give a steady pressure if pumps are variable speed controlled and if stop/start will reduce the frequency.

These are multi stage pumps capable of high pressure. do you think I can close the main discharge valve fully with out damaging anything.
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I might be missing something, but assuming the pump(s) are on either their P1 or P2 curves that's how they are intended to operate. They reduce their outlet pressure when the flow is reduced. This is usually an energy saving measure. The spec for the pump is here:

CR 10-4 A-A-A-E-HQQE

Vertical, multistage centrifugal pump with suction and discharge ports on the same level. The pump head and base are in cast iron - all other wetted parts are in stainless steel (EN 1.4301)

product-selection.grundfos.com

I'd like to stress my correction to the wrong info I provided. I did made the correction already but it appears that Chuck haven't seen it. Actually when I open valve 1 pressure decrease. And since pump 1 is also running. pressure must increase but the opposite happened.

 

[Danb]

Sounds like you just lose your head when pump are off or valve closed. Imagine a vertical pipe pump push water to the to keeping pressure up. When pump of of valve closes allows water to settle under it's own pressure and drops abit.
Just a thought
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Might explain the pressure drop,
Because you don't lose all pressure do you just partial.
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Might explain the pressure drop,
Because you don't lose all pressure do you just partial.

 

[Chuck]

I'd like to stress my correction to the wrong info I provided. I did made the correction already but it appears that Chuck haven't seen it. Actually when I open valve 1 pressure decrease. And since pump 1 is also running. pressure must increase but the opposite happened.

I haven't read the entire thread but that is what should happen if the pumps are in PP mode. When there is one pump running you have flow Vdot and head deltaP across the pump. Put a second pump in parallel then the flow per pump is halved so deltaP is also reduced. Depending on what's drawing the flow, that may also drop causing the pumps to reduce the pressure even further.

A smart pump doesn't need an external flow meter to operate, the flow is proportional to the pump RPM, which the motor controller knows. Also, don't forget that the 'pressure' referred to on pump curves is the pressure difference (hence deltaP) across the pump, not the outlet pressure.

 

[John.g]

Just thinking there again re these pumps, P1 and P2 refer to pump efficiency and pump+motor efficiency and grundfos give them on all sort of fixed speed pumps and even though pump pressures vs valve throttling can only logically be explained by some form of speed control I really wonder are these smart pumps like their much smaller domestic circulator cousins?.

 

[Julian]

Sounds like you just lose your head when pump are off or valve closed. Imagine a vertical pipe pump push water to the to keeping pressure up. When pump of of valve closes allows water to settle under it's own pressure and drops abit.
Just a thought
[automerge]1573718465[/automerge]
Might explain the pressure drop,
Because you don't lose all pressure do you just partial.
[automerge]1573718467[/automerge]
Might explain the pressure drop,
Because you don't lose all pressure do you just partial.

I'm pretty sure I still have my head in 1 piece. hahaha. Kidding aside I think the first step is to make sure this is a or not a variable speed intelligent pump system.
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I haven't read the entire thread but that is what should happen if the pumps are in PP mode. When there is one pump running you have flow Vdot and head deltaP across the pump. Put a second pump in parallel then the flow per pump is halved so deltaP is also reduced. Depending on what's drawing the flow, that may also drop causing the pumps to reduce the pressure even further.

A smart pump doesn't need an external flow meter to operate, the flow is proportional to the pump RPM, which the motor controller knows. Also, don't forget that the 'pressure' referred to on pump curves is the pressure difference (hence deltaP) across the pump, not the outlet pressure.

Thanks again, very nice tutorial on intelligent pumps but still does not explain the phenomena I have observed. Logically an intelligent pump system should minimize bill while giving the same pressures on the taps as the dumb pumps. That said an IPS must maintain same pressure on the taps at all times. I am imagining when all taps are close both pumps must be on standby. When one tap is opened primary pump kicks in at minimum speed and then increase speed as more taps is opened. When more taps are in service that primary pump cannot cope up, back up pump kicks in. If IPS lose pressure when closing discharge valve then its a dumb pump or in other words there is something wrong with it. The only thing I can think of is the control system starting from the transducer to the receiver/ interpreter. But I Will go and do as Snowhead suggested and perform same test as before to make sure. Now I am seriously considering that I indeed lose my head momentarily hahaha.

 

[Julian]

Just thinking there again re these pumps, P1 and P2 refer to pump efficiency and pump+motor efficiency and grundfos give them on all sort of fixed speed pumps and even though pump pressures vs valve throttling can only logically be explained by some form of speed control I really wonder are these smart pumps like their much smaller domestic circulator cousins?.

Most probably yes because I still don't see any explanation to losing pressure when main discharged valve is closed other than the pump is trying to maintain a constant pressure.

 

[John.g]

I have a smart (circulating) pump which I can run in any one of three modes, Fixed Speed, Constant Pressure and Proportional Pressure mode and here is what the effect would be on the pressure indication if the pumps that we are discussing were run in these three modes bearing in mind where this pressure gauge is fitted. (manifold)
Both pumps running in all cases.
Fixed Speed: Open v/v1, pressure increase. Close main v/v, pressure increase.
Constant pressure: Open v/v1, no pressure change. Close main v/v, no pressure change.
Proportional Pressure: Open v/v1, pressure decrease. Close main v/v, pressure decrease.

If they are not "smart" pumps (which don't measure flow or pressure) it would seem that they are being controlled from somewhere in proportional pressure (PP) control using the pressure transducer on the manifold and pump power although one might think that constant pressure mode would be more appropriate.
As pointed out in post#27, one should hear the pumps speeding up/down if running in variable speed mode.

 

[Julian]

I have a smart (circulating) pump which I can run in any one of three modes, Fixed Speed, Constant Pressure and Proportional Pressure mode and here is what the effect would be on the pressure indication if the pumps that we are discussing were run in these three modes bearing in mind where this pressure gauge is fitted. (manifold)
Both pumps running in all cases.
Fixed Speed: Open v/v1, pressure increase. Close main v/v, pressure increase.
Constant pressure: Open v/v1, no pressure change. Close main v/v, no pressure change.
Proportional Pressure: Open v/v1, pressure decrease. Close main v/v, pressure decrease.

If they are not "smart" pumps (which don't measure flow or pressure) it would seem that they are being controlled from somewhere in proportional pressure (PP) control using the pressure transducer on the manifold and pump power although one might think that constant pressure mode would be more appropriate.
As pointed out in post#27, one should hear the pumps speeding up/down if running in variable speed mode.

What is the proportional pressure system? Does this mean that both pumps have proportional discharge pressure or that the pressure after and before main valve are the same?

 

[John.g]

Proportional pressure (PP) control is used mainly in heating systems with radiator thermostatic valves which throttle in the flow rates through the rads to give the desired room temperatures, in normal fixed speed pumps the pump head increases as the flow rate decreases but because the pipe friction losses decrease with decreasing flow then PP mode when selected is designed to reduce the pump head with reducing flow rates proportionally and because it is based on the theory that half the losses are in the pipework and the other half are in the rads then the PP minimum set point is 1/2 of the PP maximum setpoint. For example, I have my circ pump selected to a PP setting of 4M which is looking for a flow rate of 23 LPM and at zero flow rate will have a head of 2M So quite simply put if I connected my pump to a water supply and put a tap on the other end and shut it then the pump pressure would remain at 2M and if I started opening it then it would give a flowrate of 11.5 LPM at 3M and 23 LPM at 4M.
In your case IF and only IF there is some form of proportional control then simply shutting the main discharge valve will give the minimum set point pressure, whatever that is, and as you start re opening the main discharge valve the pump pressure should start increasing towards its maximum pp setting (assuming the neccessary flow demand.)

As was asked a number of times before can you hear the pump(s) speed changing? if not then back to the drawing board.

 

[Julian]

Proportional pressure (PP) control is used mainly in heating systems with radiator thermostatic valves which throttle in the flow rates through the rads to give the desired room temperatures, in normal fixed speed pumps the pump head increases as the flow rate decreases but because the pipe friction losses decrease with decreasing flow then PP mode when selected is designed to reduce the pump head with reducing flow rates proportionally and because it is based on the theory that half the losses are in the pipework and the other half are in the rads then the PP minimum set point is 1/2 of the PP maximum setpoint. For example, I have my circ pump selected to a PP setting of 4M which is looking for a flow rate of 23 LPM and at zero flow rate will have a head of 2M So quite simply put if I connected my pump to a water supply and put a tap on the other end and shut it then the pump pressure would remain at 2M and if I started opening it then it would give a flowrate of 11.5 LPM at 3M and 23 LPM at 4M.
In your case IF and only IF there is some form of proportional control then simply shutting the main discharge valve will give the minimum set point pressure, whatever that is, and as you start re opening the main discharge valve the pump pressure should start increasing towards its maximum pp setting (assuming the neccessary flow demand.)

As was asked a number of times before can you hear the pump(s) speed changing? if not then back to the drawing board.

Thanks for the tutorial.
I was there today and conducted the speed changing test. Put my ear right on the body of pump two and slowly open valve 1 ( currently about 20% open) until full open. Pressure drop from 70 to 60. Not a bit changed in speed. Close it again until I can hear the water straining to the almost close. pressure rise to around 83. not a bit changed in speed. Put my ear on pump 1 one and perform same test. Not a bit change in speed. As I perform the test I kept feeling both pumps discharge line. I can tell that pump two is straining or doing some work while pump one seems to be not doing any work. It is possible that pump one is not working. Motor is running but pump is not moving water. If I had my clamp ammeter with me I would have conducted an ampere test but I did not bring it with me. so will have to go back and test again.
Here is What comes to mind while doing the test. Pump one is broken and NRV one is also broken and that water is going back that route. Have inspected the cistern I can't see any foot valve although it wasn't very clear deep in the water. Maybe RPM "stab in the dark" hit its mark. Did not conduct the Main valve test as I was alone, and main valve is high up. I will need an assistant to do the test.. This is an unplanned test. I was there for emergency call regarding fire alarm. took some pictures.

 

[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.