2 bar vs 3 bar water pumps

[XLD]

Can someone explain what the difference is if they both deliver the same litres per minute?

[TheBiscuits]

 

One bar.

 

Glad I could help.

 

🤣

[Alan de Enfield]

Approximately 14.5 psi in proper units

[Arthur Marshall]

Apparently not!

[Tony Brooks]

16 minutes ago, XLD said:

Can someone explain what the difference is if they both deliver the same litres per minute?

 

Bar is only the cut-out pressure, there should also be litres or gallons per minute in the specifications. That is what you want to look at for a comparison of delivery volume. So the same litres per minute give the same delivery volume. The difference is the 3 bar pump might require a new PRV on the calorifier or its cut out pressure adjusting downwards to 2 bar. Unless adjusted down, it could cause a plumbing leak. Running a tap into the bathroom hand basin is more likely to get you an embarrassing wet patch on your trousers (depending upon bowl design).

[XLD]

8 minutes ago, Tony Brooks said:

 

Bar is only the cut-out pressure, there should also be litres or gallons per minute in the specifications. That is what you want to look at for a comparison of delivery volume. So the same litres per minute give the same delivery volume. The difference is the 3 bar pump might require a new PRV on the calorifier or its cut out pressure adjusting downwards to 2 bar. Unless adjusted down, it could cause a plumbing leak. Running a tap into the bathroom hand basin is more likely to get you an embarrassing wet patch on your trousers (depending upon bowl design).

So the pressure in the pipework is higher and more suseptable to leakage?

[Alan de Enfield]

To get the same flow rate (ie lts per minute) the 3 bar system must be using a smaller dimeter pipe than the 2 bar.

 

Its like water coming out of a hose, it runs out at a reasonable rate, but , the jet doesn't go very far.

Put your finger over the end to reduce the pipe size and you get the same flow rate but the jet goes further as it is at a higher pressure.

 

Its a bit like 'watts are fixed', but voltage and amps can vary, so 

W=A x V

W = A/2 x 2V

 

etc

[blackrose]

Flow rate in units of litres/minute is different from pressure in bar or psi. So you can buy a pump that produces the same flow rate at different pressures.

 

I changed my Parmax 25psi pump a couple of years ago to a Parmax 40psi pump in an attempt to get my instant gas water heater to work properly. Both pumps had exactly the same flow rate which from memory was 13 litres/min.

 

A few of the usual suspects here said what I was proposing wouldn't work because what I needed was a higher flow rate pump, not higher pressure. I fitted the pump anyway because I'd already bought it some months earlier it was too late to return it. The water heater worked perfectly!

 

When I mentioned the result on the forum one of them said "Well the higher pressure has resulted in a higher flow rate", completely contradicting what he'd said previously! 😂 There is a lot of expertise on the forum but despite a high level of certainty we don't know everything.

10 minutes ago, XLD said:

So the pressure in the pipework is higher and more suseptable to leakage?

 

Only if your plumbing is cr@p.

[Tony Brooks]

9 minutes ago, Alan de Enfield said:

To get the same flow rate (ie lts per minute) the 3 bar system must be using a smaller dimeter pipe than the 2 bar.

 

Or different volume pumping chambers, but I suspect the chambers are all the same size, and it is just the cut-out pressure that has been set higher with possibly a more powerful motor. I bet the flow rate is measured at the pump outlet into zero pressure.

[Jen-in-Wellies]

Do you have a calorifier in your water system? If so, what is its maximum working pressure and what value pressure relief valve is fitted? The pump cut out pressure needs to be below the max working pressure and also slightly below the PRV pressure. The PRV, needless to say, also needs to be below the cauliflower safe working pressure.

 

40 minutes ago, XLD said:

So the pressure in the pipework is higher and more suseptable to leakage?

Only if the pipework is really rubbish. In competently installed plumbing it will make no difference, but see cauliflower above. For comparison, typical mains pressure from the pipe coming in to most homes is around 6 bar and that only leaks if there is a problem.

[Paul C]

When a tap is open, the pressure isn't 3 bar (or 2 bar), its just the pressure/head needed to get the water through the relevant length of pipework, around its bends, and up to the tap. Its going to be in the region of 0.1 bar. So, they'll both flow at their near maximum flowrate.

 

A higher flowrate pump needs more power (but it will be the same energy from the battery.........because the same amount of work is being done, its just quicker) so in theory thicker wires, etc so you can't just swap out a low flowrate pump for a super high one. But if you can, then I'd always recommend a higher flowrate - its just nicer to use, instead of waiting and waiting for water to flow eg into a bucket or basin.

[Jen-in-Wellies]

4 minutes ago, Paul C said:

When a tap is open, the pressure isn't 3 bar (or 2 bar), its just the pressure/head needed to get the water through the relevant length of pipework, around its bends, and up to the tap. Its going to be in the region of 0.1 bar. So, they'll both flow at their near maximum flowrate.

 

A higher flowrate pump needs more power (but it will be the same energy from the battery.........because the same amount of work is being done, its just quicker) so in theory thicker wires, etc so you can't just swap out a low flowrate pump for a super high one. But if you can, then I'd always recommend a higher flowrate - its just nicer to use, instead of waiting and waiting for water to flow eg into a bucket or basin.

Also the headline flow rate quoted by the manufacturer is flow with it not actually connected to any downstream plumbing. The resistance from the pipe, fittings, bends and so on reduce it considerably. For example, on my boat, I get 6l/min at the taps from a pump that is supposed to deliver 11l/min. Shorter distances, bigger diameter pipes, fewer fittings and bends would all improve the flow rate to closer to the official figure.

[Alan de Enfield]

Analogy :

 

Remember when you were young and won all the 'highest peeing up the wall' competitions - that was a 3 bar pump

 

 

Now you are old  and having to take care you don't pee on your feet - that is a 2 bar pump

[alan_fincher]

13 hours ago, Alan de Enfield said:

Analogy :

 

Remember when you were young and won all the 'highest peeing up the wall' competitions - that was a 3 bar pump

 

 

Now you are old  and having to take care you don't pee on your feet - that is a 2 bar pump

 

2 Bar?  2 Bar??

I can only dream of 2 Bar!

[XLD]

Right. I have a 2 bar pump on my hot water system and  a 2 bar pump on my coldwater system. (so if one packs in l dont lose the whole water supply).
What happens if l replace  one with a 3 bar pump. Thinking of the mixer shower. 
Serious answers only please

[Paul C]

The 3 bar will probably achieve a higher percentage of the nominal flowrate in its specification, all else being equal. So you'd need to make some kind of adjustment on the mixer shower, with the mixer control you already have.

 

But as stated before, it won't ACTUALLY be anywhere near 3 bar (or 2 bar) the pump is pressurising the water to, it will be in the order of 0.1-0.5 bar as determined by the pipework inner diameter, length, number of bends/fittings etc and how much open the tap/flow control lever of the shower is.

 

 

[XLD]

Thanks for all the serious educated comments👍

[MtB]

The 2 and 3 bar specifications are the peak pressures the pumps can generate pumping against a closed tap or capped pipe. So of no particular use or interest when assessing the likely performance of the pump through an open pipe or open tap. For this, you need to look up and compare the maximum flow rate the pumps can deliver.

 

The static pressure is something only marketing departments obsess over. No-one knows why.

 

If you have a calorifier the 2 bar pump is more appropriate as the PRV is probably 3 bar opening pressure, so you don't want the static pressure in the system rising that high, or anything even close. 

[cuthound]

54 minutes ago, MtB said:

The static pressure is something only marketing departments obsess over. No-one knows why.

 

 

Marketing departments love big numbers, the bigger the better!

 

They do this with diesel engines generators. They always quote kVA rather than kW.

 

Now a well matched diesel engined generator set will have a diesel engine that can only deliver enough mechanical power to turn an alternator at its rated output 

 

So for a 1000kVA  generating set, rated at 0.8 power factor, it will deliver a maximum of 800kVA. Improve the power factor to unity and it will still only deliver 800kVA because that is the maximum power the engine can deliver (unless the generator set has been specified at a continuous or "sprint"rating in which case it can deliver a bit more than its rated power for a specified limited time).

 

However the bigger numbers look more impressive.