Dingdongler

Can anybody explain the difference between dynamic and static pressure in your home water system? How and where should these two measurements be taken?


Thanks

albob

i have a combi boiler - when it is off, the pressure indicator sits at 1 bar : when it is on the indicator sits at 2 bar.

static and dynamic ???

ALi-B

iTrader: (1)

No, thats more likely expansion in a sealed system for your central heating (thats what the gauge on a typical combi says - to let you know when it needs refilling or when the expansion vessel is knackered).

Dingdong is on about the mains water pressure;

Static is the pressure with zero water flow - all taps off.
Dynamic is the pressure measured when all the taps are turned on, or at least serving with the expected demand.

The closer the values are to each other the better. As you don't want pressure drops as more taps are turned on or on the taps on the longest/most restrictive pipe run....especially with non-thermostatic mixer taps.

Been though all this at my house as it was originally served with a 15mm incomming main and went through valves/stopcocks which had a 10mm internal diameter...to serve the entire house! Suffice to say static pressure was excellent...around 7bar IIRC....dynamic pressure?.....a pathetic 1.5bar when more than two taps were running. You can imagine how annoying that is when somone flushes a toilet whilst you are taking a shower

Dingdongler

Thanks Ali.

When speccing a new dhw system I've been reading that the dynamic pressure reading is the one of importance and that the static reading is misleading and not very helpful.

I need my dhw system replaced/over hauled and have had two plumbers come around to quote. The first only measured the pressure after I insisted. The second I thought was going to do better as himself wanted to come back at 0700hrs to measure the pressure/flow at the time of peak demand.

But again he only measured static pressure!

ALi-B

iTrader: (1)

I had this probelem; Had a couple of plumbers round and none were interested. In flow rates or dynamic pressure.

i.e They turn one tap on, see plenty of flow and say whats the problem?

They seemed to think becuase the pipes to the taps are 10mm or 15mm its ok to have everything else 15mm too (bearing in mind I found most newer 15mm valves have 10mm internals- thats a huge restriction). Ended up getting a builder to do most of it (with me doing other bits and bobs).

Dingdongler

This guy I called is meant to be more than a jobbing plumber, he does large central London pads (I don't own a large central London pad btw!) and blocks of flats etc.

He was making all the right noises about flow, pressure, coil kw ratings etc and did himself say he needed to measure pressure and flow. I'm just surprised he didn't measure the dynamic pressure...