Plumbase Christmastime
This official sponsor may provide discounts for members

Discuss Two pumps connected in parallel runs continuously in the Plumbing Forum | Plumbing Advice area at PlumbersForums.net

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.
 
Plumbase Perks - Special offers for forum members
This official sponsor may provide discounts for members

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.
 
Last edited:
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.
Post automatically merged:

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?
 
Last edited:

snowhead

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.
Post automatically merged:

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.
 

Danb

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

 
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.
 
Last edited:
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.
Post automatically merged:

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.
Post automatically merged:

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:

Thanks Chuck. If this is the case there should be a flow sensor. I did not see one. But I will check again.
 
Last edited:
"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.
Post automatically merged:

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.
Post automatically merged:

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.
Post automatically merged:

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.
Post automatically merged:

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:

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.
 
Last edited:

Danb

Gas Engineer
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
Post automatically merged:

Might explain the pressure drop,
Because you don't lose all pressure do you just partial.
Post automatically merged:

Might explain the pressure drop,
Because you don't lose all pressure do you just partial.
 
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.
 
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?.
 
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
Post automatically merged:

Might explain the pressure drop,
Because you don't lose all pressure do you just partial.
Post automatically merged:

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.
Post automatically merged:

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.
 
Last edited:
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.
 

Reply to Two pumps connected in parallel runs continuously in the Plumbing Forum | Plumbing Advice area at PlumbersForums.net. Plumbing questions, answers, tips and tricks.

Test4Less - PlumbersForums.net Sponsor
This official sponsor may provide discounts for members
Bulk Workwear - Workwear Sponsor for Plumbers Forums
uHeat Forum Sponsor - PlumbersForums.net
Plumbing Advice - Find Plumbers Jobs
Corgi Direct - Plumbers Forums Sponsor
Power Shower Booster - Official PlumbersForums.net Sponsor
Test4Less PlumbersForums.net Sponsor
Plumbase - PlumbersForums.net Sponsor
Wetroom Store - PlumbersForums.net Sponsor

New Posts Threads Members

CorgiDirect - Discounted Corgi Related Documentation and Plumbing Supplies
This official sponsor may provide discounts for members
Top