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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.
 

Attachments

rpm

Esteemed
Plumber
Grundfos CR10`s 12m head multi-stage booster pumps there. One speed non variable 3kw motors @ 3500rpm and no pressure transmitter on them. Don`t understand why you would want to throttle back the discharge or are you getting cavitation.
 
Grundfos CR10`s 12m head multi-stage booster pumps there. One speed non variable 3kw motors @ 3500rpm and no pressure transmitter on them. Don`t understand why you would want to throttle back the discharge or are you getting cavitation.
I'm just testing if the pump can still deliver more pressure. There is a pressure transmitter installed next to the pressure gauge.
 

Danb

Gas Engineer
Is that the boosted cold
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Does it feed a tank onntop of the four storys?
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Its trying to maintain a constant pressure.
When you close it do you only lose pressure on one side
 
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rpm

Esteemed
Plumber
What is this pressure transmitter, can you post photos of it please?
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I'm just testing if the pump can still deliver more pressure. There is a pressure transmitter installed next to the pressure gauge.
Is that the boosted cold
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Does it feed a tank onntop of the four storys?
Looks like it is in a workshop at the moment.
 
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Is that the boosted cold
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Does it feed a tank onntop of the four storys?
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Its trying to maintain a constant pressure.
When you close it do you only lose pressure on one side
Yes it is boosted cold
No it does not feed a tank on the top floor it has a pressure tank next to it.
Its connected in parallel so both lose pressure. Yes I think its trying to maintain a constant pressure
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What is this pressure transmitter, can you post photos of it please?
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Looks like it is in a workshop at the moment.
The transmitter has a wire that runs to the control board. That is why I was thinking that maybe " the control board sends command to the motor based on the transmitter reading" That is why I was thinking the motor is variable speed. I dont see an auto bypass valve either.
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there is only one pressure gauge on the discharge side of both pumps that sits next to the pressure transmitter.
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The pressure transmitter is connected to the pressure gauge with a tee and has wire that goes to the control board
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I think the reason it runs continuously is because its trying to maintain a constant pressure that does not go up to the set cut out pressure.
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I am sorry I think I had said something wrong. Please refer to the layout drawing I made as I try to explain. Actually the discharge valve1 is currently 20% or so open so like 80% close. Whenever I try to open it pressure drops. When I close main discharge valve pressure also drops. So yes I think its trying to maintain a constant pressure. But if it does, why does the pressure dont recover. I have watch there for like 2 min and the pressure never recover. How long does a pressure of such a system recovers? Whenever I close main valve or open valve1 pressure drops within a minute.
 

Attachments

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rpm

Esteemed
Plumber
It won`t recover pressure, are you getting flow & pressure mixed up. A quick look at Grundfos site say`s outlet should be DN40 which I don`t think you`re showing in the photographs. You won`t get more out than the manufacture states by adjusting inlet/ outlet valves, if anything you will kill it.
 

Danb

Gas Engineer
Looks to me the the pressure transducer notices pressure drop and kicks selected pump in. When its satisfied turns them off.
If there no non returns with the head off water it pass back through pump 1 when you open valve 1.
Also whats the min and max pressure settings set at?
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The pressure tank next to it that you mentioned,
Should think this is more likely the cold feed for the pump to make sure it has volume behind it .
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Agree with rpm these are on off pump sets.
 
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rpm

Esteemed
Plumber
You mentioned increasing the pressure , you can buy a service kit for these if they are down on duty. I've recon these on site lots of times.
 
Looks to me the the pressure transducer notices pressure drop and kicks selected pump in. When its satisfied turns them off.
If there no non returns with the head off water it pass back through pump 1 when you open valve 1.
Also whats the min and max pressure settings set at?
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The pressure tank next to it that you mentioned,
Should think this is more likely the cold feed for the pump to make sure it has volume behind it .
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Agree with rpm these are on off pump sets.
two pumps run continuously 24/7. But you're right there is no non returns on the head off. I think you're correct with the pressure tank because its just a small one. Not the size to service an entire building. that solves one of my concerns. Excuse my ignorance but what is an "on off pump set"
 

snowhead

Esteemed
Plumber
Excuse my ignorance but what is an "on off pump set"
When the pressure drops below the cut in set point the pump(s) switch ON and run at their maximum speed.
When the pressure in the system reaches the cut off set point, the pump(s) switch OFF.

Modern pump systems are variable speed, so the pump(s) reduce speed to keep the pressure constant.

Have you checked that there is no air trapped in the pumps?
 

oz-plumber

Esteemed
Plumber
Quite a lot of variables with this one and it could be a situation where you start with the basics and go on from there.

1/ non-return valves on outlets of pumps
2/ pressure switches - faulty, not calibrated, not connected.
They are there, but not switching off the pumps - obviously not working as intended.
3/ Pressure vessel - shouldn't have much to do with the operation of the pumps or pressure switches on the pumps. It's only there to stop a lag in water pressure when the pumps are stopped and the pressure switch hasn't activated ( very basic description of what it does )
 

rpm

Esteemed
Plumber
Unless I`m looking at this all wrong I would expect to see two pressure gauges on the discharge pipes or one on the pipe after they merge together if they do this.
Also wondering if a photo of the control board might help.
 
There seems to be two different pumps fitted, one is 12.1 m3/hr, 47.2 M head @ 3550 RPM, the other nameplate shows a 50HZ pump, 2990 RPM, can't see the flow/head so if fitted in the philippines will run at 60 HZ so maybe thats fitted in position 1 and throttled in to prevent o/load trip out (pump affinity laws). If so, it seems a very strange match but whatever the set up, there should most certainly, as pointed out above, be NR valves fitted because not only will you get reverse flow through the pump, you can/will also get reverse rotation of the pump which will result in motor burnout on auto restart or if restarted without manually shutting the discharge valve.
 
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There seems to be two different pumps fitted, one is 12.1 m3/hr, 47.2 M head @ 3550 RPM, the other nameplate shows a 50HZ pump, 2990 RPM, can't see the flow/head so if fitted in the philippines will run at 60 HZ so maybe thats fitted in position 1 and throttled in to prevent o/load trip out (pump affinity laws). If so, it seems a very strange match but whatever the set up, there should most certainly, as pointed out above, be NR valves fitted because not only will you get reverse flow through the pump, you can/will also get reverse rotation of the pump which will result in motor burnout on auto restart or if restarted without manually shutting the discharge valve.
Edit: Maybe both 60hz pumps have 50 hz motors fitted and the installation is in the UK.
 
When the pressure drops below the cut in set point the pump(s) switch ON and run at their maximum speed.
When the pressure in the system reaches the cut off set point, the pump(s) switch OFF.

Modern pump systems are variable speed, so the pump(s) reduce speed to keep the pressure constant.

Have you checked that there is no air trapped in the pumps?
Ok so this is not a variable speed pump and I should stop looking from that angle.
I will try to air purge the pumps.
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Quite a lot of variables with this one and it could be a situation where you start with the basics and go on from there.

1/ non-return valves on outlets of pumps
2/ pressure switches - faulty, not calibrated, not connected.
They are there, but not switching off the pumps - obviously not working as intended.
3/ Pressure vessel - shouldn't have much to do with the operation of the pumps or pressure switches on the pumps. It's only there to stop a lag in water pressure when the pumps are stopped and the pressure switch hasn't activated ( very basic description of what it does )
You could be correct about all of these. But how does this correlate to the dropping of pressure whenever I make adjustment on valves that is suppose to increase pressure. If pump maintains speed and power closing outlet valve should increase pressure in between valve and pump where the pressure gauge (and transducer) is located, no exception. also opening valve one full (which is currently about 20% open) should increase pressure, but the opposite happens. What other explanation could there be, if there is any. other than the pump is "trying to maintain a constant pressure". You see I don't want to touch anything until I am able to connect all the dots. This is a hotel and I don't want to trouble the guests as that won't be good for the owners.
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Unless I`m looking at this all wrong I would expect to see two pressure gauges on the discharge pipes or one on the pipe after they merge together if they do this.
Also wondering if a photo of the control board might help.
I will take photo of the control board and more photo of the system when I go visit again. I am not hurrying with this one. I told the client that I wont touch anything unless I am absolutely sure of what to do and that they can hire someone if they want to.
 
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Danb

Gas Engineer
Without seeing the set up is hard to say for certain but It looks like to me that there for constant cold pressure.
As mentioned earlier.
Fit nrvs for a start.
Check min and max pressure settings, mechanical or digital control.
Make sure pump supply tank.is large enough to cope with demand,
As mentioned earlier you may get air in system if the tank runs dry And get pump issues.
 
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.
 

Danb

Gas Engineer
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
 

rpm

Esteemed
Plumber
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.
 
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.
There seems to be two different pumps fitted, one is 12.1 m3/hr, 47.2 M head @ 3550 RPM, the other nameplate shows a 50HZ pump, 2990 RPM, can't see the flow/head so if fitted in the philippines will run at 60 HZ so maybe thats fitted in position 1 and throttled in to prevent o/load trip out (pump affinity laws). If so, it seems a very strange match but whatever the set up, there should most certainly, as pointed out above, be NR valves fitted because not only will you get reverse flow through the pump, you can/will also get reverse rotation of the pump which will result in motor burnout on auto restart or if restarted without manually shutting the discharge valve.
Edit: Maybe both 60hz pumps have 50 hz motors fitted and the installation is in the UK.
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.
 
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Without seeing the set up is hard to say for certain but It looks like to me that there for constant cold pressure.
As mentioned earlier.
Fit nrvs for a start.
Check min and max pressure settings, mechanical or digital control.
Make sure pump supply tank.is large enough to cope with demand,
As mentioned earlier you may get air in system if the tank runs dry And get pump issues.
Another thing that does not look right is that the pressure tank is very small for the system. 30 gal or so. This are are digitally control. Did not see any mechanical PS. I will take more pictures.
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Forgive my insistence, But I wanted to correlate every suggestion to the phenomena of pressure decrease whenever I close outlet valve. Unless we can explain this phenomena its more of a hit and miss. I will go and gather more info and take more photo. Thanks again. But before I go. Does anyone have a suggestion on what to check? Also I wanted to make sure that this is not a variable speed system. How do I do that?
 
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snowhead

Esteemed
Plumber
Also I wanted to make sure that this is not a variable speed system. How do I do that?
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.
 

rpm

Esteemed
Plumber
Stab in the dark - Is motor rotation correct and inlets & outlets of the pump the right way round?

Why put NRV on inlet side?
 

Danb

Gas Engineer
Check your nrv before pumps seen then fail before.
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Trying to up load pics of a system I see today says there to big.
Had transducers variable pumps and a large feed tank
 
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.
 

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