Dynamic pressure equals static pressure

indus · 3 Jun 2013

Hi

I've read the professionals on here often talk about how important the dynamic pressure reading is as compared to a static reading.

So having bought a gauge from Amazon today

I took some readings.

My static pressure at the garden tap is 2.8bar. When I open the kitchen tap full blast the pressure at the garden tap is still 2.8 bar. The flow happens to be 19l/min.

So, what does it mean if the static pressure is exactly the same as the dynamic pressure?

Thanks

hansthebear · 3 Jun 2013

pressure reducing valve on the incoming main?

Porque223 · 3 Jun 2013

indus said:
My static pressure at the garden tap is 2.8bar. When I open the kitchen tap full blast the pressure at the garden tap is still 2.8 bar. The flow happens to be 19l/min.

One possibility is that the capacity of the system upstream of your garden tap is way more than 19 liters/min.
Was it 2.8 bar or 2.80 or 2.800?

Dan Robinson · 3 Jun 2013

Garden tap has a check valve in it.

indus · 3 Jun 2013

Dan/Hans, can you explain what you mean please?

Dan Robinson · 3 Jun 2013

Pressure reducing valve, if present and set to 2.8, and there is more pressure available will allow more in to maintain the pressure.

If the garden tap has a check valve then with a gauge on the outlet and negative pressure in the system, the pressure gauge will hold steady.

Put the pressure gauge on a washing machine valve and do the test again.

Onetap · 3 Jun 2013

hansthebear said:
pressure reducing valve on the incoming main?

Pressure reducing valve set at 2.8 bar. Mains/street pressure is 5 bar, say. Turn on kitchen tap, pressure would typically fall to say 1.8 bar, except PRv opens up to keep the downstream pressure at 2.8 bar.

Do you have a Megaflo?

indus · 3 Jun 2013

Hi Onetap/Dan

I don't have a Mega Flo, I have a thermal store.

I've had a look and I do seem to have a PRV but it seems to be after the garden supply is tapped off the mains. In the pic below you can see the mains coming up from the floor, the unlagged pipe you see tapped off is what I presume to be the garden outlet. The PRV is then fitted after that.

Dan Robinson · 3 Jun 2013

Turn the water off and remove that little grey cap and fit a pressure gauge.

Happy days.

indus · 4 Jun 2013

Hi Dan

Will measuring the pressure from the grey cap tell me the true potential pressure in the system?

Thanks

Dan Robinson · 4 Jun 2013

It'll beat fannying around with garden taps.

indus · 4 Jun 2013

Thanks.

So should I switch the stop cock off, remove grey cap, attach gauge and then re open stop cock?

Agile · 4 Jun 2013

I am not sure what you are going to do or why you are suddenly so interested.

But you can buy a pressure gauge, usually 0-6 bar and screw it into the port currently closed by the knurled grey plug.

Tony

Onetap · 4 Jun 2013

indus said:
Hi Dan

Will measuring the pressure from the grey cap tell me the true potential pressure in the system?

Thanks

That port shows the pressure downstream of the PRV which will/should be about 3 bar, or 2.8 bar with your meter.

It would only fall below 2.8 bar with a draw-off if excessive restrictions in the pipes prevented enough water passing to maintain 2.8 bar (what you're checking for), or if the upstream mains pressure was too low.

indus · 4 Jun 2013

Thanks Onetap.

Tony, at present I have a TS which is buggered and needs replacing. I want to decide whatsort of system to replace it with. Whenever that question is asked on this forum you professionals all ask what the flow, pressure and dynamic pressure is. That is why I wanted to measure it.

What I have noticed is that if I have a shower running and then open a tap there is a significant negative change in the amount of water coming out of the shower. Whether this is a flow of pressure issue I have no idea.

One of the things I want to resolve with the new system is this issue, ie two outlets should run at the same time with no discernable drop in water delivery.

Thanks

diynot

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Dynamic pressure equals static pressure

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