How does an accumulator work?

[indus]

Hi

I understand that an accumulator holds a body of cold water stored at near mains pressure by a diaphragm. I'm just a little confused by what triggers it into action.

Let's say you have an existing flow rate of 40l/min and you have a 500l accumulator (that holds 250l) and an unvented cylinder.

If you then switch on two showers at 15l/min ie 30l/min total then will the accumulator stay 'off' as the demand is within the existing fow rate? Or would the accumulator discharge itself first and then you become dependant on the mains flow rate once it is empty?

Thanks

 

[Dan Robinson]

40 in 30 out would mean that the accumulator is unnecessary and wouldn't discharge.

All an accumulator is is a big balloon.

 

[indus]

Thanks Dan.

Let's say it's still the same 40l in but now it becomes 50l out due to extra demand. That leaves a deficit of 10l/min. Will the accumulator now just discharge to bridge the gap ie will it discharge at just a rate of 10l/min?

Many thanks

 

[dcawkwell]

Thanks Dan.

Let's say it's still the same 40l in but now it becomes 50l out due to extra demand. That leaves a deficit of 10l/min. Will the accumulator now just discharge to bridge the gap ie will it discharge at just a rate of 10l/min?

Many thanks

Yes the accumulator will start discharging at 10 litres a minute while
demand remains at 50litres /minute.

 

[indus]

Thanks d'well.

What actually causes the accumulator to 'trigger'? Does it sense a drop in pressure or flow rate?

Cheers

 

[swbjackson]

Nothing "triggers" the accumulator. It's a large expansion vessel. The incoming main will compress the gas on one side of the diaphragm and the remainder of the vessel will fill with water at the standing pressure. If a draw off exceeds the incoming flow rate the pressure will reduce in the pipework. This pressure will now be less than the air pressure behind the diaphragm which will expand to equalise pressure and push water back out making up the shortfall.

 

[dcawkwell]

Thanks d'well.

What actually causes the accumulator to 'trigger'? Does it sense a drop in pressure or flow rate?

Cheers

There is compressed air in the accumulator. When no water is flowing the pressure in the accumulator and mains cold pipes will be equal. When water is flowing from the mains that doesn't meet the demand the pressure in the accumulator will
be higher than the pressure from the mains and water will leave the accumulator. When pressure in the mains cold pipes is greater than the accumulator the accumulator will fill.

 

[indus]

Thank you very much

 

[indus]

Dcawkwell, I've just found an old thread where you were thinking of fitting one.

Did you?

Thanks

 

[dcawkwell]

Dcawkwell, I've just found an old thread where you were thinking of fitting one.

Did you?

Thanks

No. For our usage we have enough flow. If I find an old unvented cylinder
I might use that in future but I have decided to leave the UK so doing
anything to the house here isn't really worth it.