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.
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- Thread starter Julian
- Start date
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.
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.
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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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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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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.
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.
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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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"
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?
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 )
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 )
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.
Edit: Maybe both 60hz pumps have 50 hz motors fitted and the installation is in the UK.
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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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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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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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.
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.
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.
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