Low pump pressure

[YoungPretender1888]

Hi everyone, I’m looking for a bit of advice on how to fix low pressure from 1 of the pumps on my system. So the system is a 2 man DI only system. The pump closest to the tank outlet has normal pressure, the second pump has noticeably lower pressure at the brush head. The battery is fairly new and has enough charge, no noticeable leaks, the strainer is clean.

One thing I’ve noticed is when I disconnect the hose from the DI bottle and try to suck through any air locks, there’s a lot of resistance when sucking the water through, as if there’s a blockage somewhere. Any advice is appreciated. Cheers ?

 

[Pjj]

Try and have the outlets on a tee so that both can suck water and not just favour the first pump and the second one gets starved

 

[ched999uk]

To rule out a failing pump swap the 2 over. If the low pressure moves to outlet 1 then it's probably a pump issue. If low flow stays with outlet 2 then it's not a pump issue.
If it's not a pump then swap DI vessels and again see if issue moves.
That way you should find out if a pump, DI or something else like pipes or cables/connections.

 

[YoungPretender1888]

Try and have the outlets on a tee so that both can suck water and not just favour the first pump and the second one gets starved

I haven’t got the technical know how to swap the pumps unfortunately. I’ll try and drop the pressure on pump 1 and increase it on pump 2 to see if that makes any difference. I think you could be right though that pump 1 is starving pump 2.

 

[spruce]

Just a question. Are we talking water pressure or water flow?

We have a spare used Shurflo pump on the shelf that is a 3.8lpm where the standard window cleaning pumps are 5.2lpm.

 

[YoungPretender1888]

Just a question. Are we talking water pressure or water flow?

We have a spare used Shurflo pump on the shelf that is a 3.8lpm where the standard window cleaning pumps are 5.2lpm.

Pressure = flow surely? The lower the pressure the less the flow at the brush head? When connected to pump no.2 the flow of water at the brush head is less than when connected to pump no.1 basically. Apologies if I’m not making much sense.

 

[Pjj]

I haven’t got the technical know how to swap the pumps unfortunately. I’ll try and drop the pressure on pump 1 and increase it on pump 2 to see if that makes any difference. I think you could be right though that pump 1 is starving pump 2.

Try turning off pump one and see if pump two flow increases

 

[spruce]

Pressure = flow surely? The lower the pressure the less the flow at the brush head? When connected to pump no.2 the flow of water at the brush head is less than when connected to pump no.1 basically. Apologies if I’m not making much sense.

They are linked but not the same.



What can be confusing is that our pumps are usually rated at 100psi and our controllers are in segments of 100. The controller's segments are flow rates and not psi. The higher the number, the faster the pump motor turns and the higher the rate of flow out of the pipe.

There are numerous YouTube videos on the relationship between pressure and flow.

From an post a few years ago;

Mini bore will give more flow and volume of water for the same controller setting than microbore , I have had both the mini bore is heavy you can see a difference in the volume of water though , we now use microbore for windows but minibore for soft washing .

No you are trying to force the water out of a smaller orafice so pressure will increase but volume will decrease

Yep.

The problem is that as you try to force water through a smaller pipe the water will have to move quicker. This is when it becomes turbulent and the flow rate actually decreases at this point. (I copied and pasted my response from the other forum on this topic.)

A poster on one of the forums couldn't understand why a difference of 2mm hose size (8mm minibore to 6mm microbore) should make a difference in flow. Doug Atkinson from Daqua posted this in reply

It does -------, makes at least 30% reduction in flow


Take a look at this;

http://www.flourmilling.co.uk/water.html
Unfortunately this link is no longer working.

The link was referring to water flow rates through straight steel pipes. It stated that the flow rate difference between 6mm and 8mm bore steel pipe is considerable. At 4 bar the flow through 6mm pipe is 0.022 liters per second. The 8mm pipe its 0.056 liters per sec at the same pressure. So a 6mm tube will only allow fractionally less than 1/2 the volume of water at 4 bar. Our hose coiled up around a hose reel will probably reduce those figures a bit more.

Hot water will have a higher (or is it lower) viscosity (less dense) so will flow better through a smaller diamt hose. So most hot water users happily use microbore hose.


http://www.frca.co.uk/Documents/100308 Physics of flowLR.pdf

Interesting read these 7 pages. Sorry, this link is no longer working either.

Look at the difference between Laminar flow and Turbulent flow. Once fluid in a tube reaches a certain speed it become turbulent. Once it becomes turbulent it requires 4 times the amount of pressure to double the flow rate. Fluid through hose coiled on hose reels won't be laminar in flow but turbulent.

To calculate the area of a circle the formula is

A = π r2

A 6mm id hose is fractionally more than half the size of an 8mm hose.
A 3mm jet is a little more than twice the size of a 2mm jet.
A 1mm jet is about 1/4 of the size of a 2mm jet.

 

[YoungPretender1888]

They are linked but not the same.



What can be confusing is that our pumps are usually rated at 100psi and our controllers are in segments of 100. The controller's segments are flow rates and not psi. The higher the number, the faster the pump motor turns and the higher the rate of flow out of the pipe.

There are numerous YouTube videos on the relationship between pressure and flow.

From an post a few years ago;

Yep.

The problem is that as you try to force water through a smaller pipe the water will have to move quicker. This is when it becomes turbulent and the flow rate actually decreases at this point. (I copied and pasted my response from the other forum on this topic.)

A poster on one of the forums couldn't understand why a difference of 2mm hose size (8mm minibore to 6mm microbore) should make a difference in flow. Doug Atkinson from Daqua posted this in reply

It does -------, makes at least 30% reduction in flow


Take a look at this;

http://www.flourmilling.co.uk/water.html
Unfortunately this link is no longer working.

The link was referring to water flow rates through straight steel pipes. It stated that the flow rate difference between 6mm and 8mm bore steel pipe is considerable. At 4 bar the flow through 6mm pipe is 0.022 liters per second. The 8mm pipe its 0.056 liters per sec at the same pressure. So a 6mm tube will only allow fractionally less than 1/2 the volume of water at 4 bar. Our hose coiled up around a hose reel will probably reduce those figures a bit more.

Hot water will have a higher (or is it lower) viscosity (less dense) so will flow better through a smaller diamt hose. So most hot water users happily use microbore hose.


http://www.frca.co.uk/Documents/100308 Physics of flowLR.pdf

Interesting read these 7 pages. Sorry, this link is no longer working either.

Look at the difference between Laminar flow and Turbulent flow. Once fluid in a tube reaches a certain speed it become turbulent. Once it becomes turbulent it requires 4 times the amount of pressure to double the flow rate. Fluid through hose coiled on hose reels won't be laminar in flow but turbulent.

To calculate the area of a circle the formula is

A = π r2

A 6mm id hose is fractionally more than half the size of an 8mm hose.
A 3mm jet is a little more than twice the size of a 2mm jet.
A 1mm jet is about 1/4 of the size of a 2mm jet

They are linked but not the same.



What can be confusing is that our pumps are usually rated at 100psi and our controllers are in segments of 100. The controller's segments are flow rates and not psi. The higher the number, the faster the pump motor turns and the higher the rate of flow out of the pipe.

There are numerous YouTube videos on the relationship between pressure and flow.

From an post a few years ago;

Yep.

The problem is that as you try to force water through a smaller pipe the water will have to move quicker. This is when it becomes turbulent and the flow rate actually decreases at this point. (I copied and pasted my response from the other forum on this topic.)

A poster on one of the forums couldn't understand why a difference of 2mm hose size (8mm minibore to 6mm microbore) should make a difference in flow. Doug Atkinson from Daqua posted this in reply

It does -------, makes at least 30% reduction in flow


Take a look at this;

http://www.flourmilling.co.uk/water.html
Unfortunately this link is no longer working.

The link was referring to water flow rates through straight steel pipes. It stated that the flow rate difference between 6mm and 8mm bore steel pipe is considerable. At 4 bar the flow through 6mm pipe is 0.022 liters per second. The 8mm pipe its 0.056 liters per sec at the same pressure. So a 6mm tube will only allow fractionally less than 1/2 the volume of water at 4 bar. Our hose coiled up around a hose reel will probably reduce those figures a bit more.

Hot water will have a higher (or is it lower) viscosity (less dense) so will flow better through a smaller diamt hose. So most hot water users happily use microbore hose.


http://www.frca.co.uk/Documents/100308 Physics of flowLR.pdf

Interesting read these 7 pages. Sorry, this link is no longer working either.

Look at the difference between Laminar flow and Turbulent flow. Once fluid in a tube reaches a certain speed it become turbulent. Once it becomes turbulent it requires 4 times the amount of pressure to double the flow rate. Fluid through hose coiled on hose reels won't be laminar in flow but turbulent.

To calculate the area of a circle the formula is

A = π r2

A 6mm id hose is fractionally more than half the size of an 8mm hose.
A 3mm jet is a little more than twice the size of a 2mm jet.
A 1mm jet is about 1/4 of the size of a 2mm jet.

Thanks a lot for the info ?