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https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl DIY Forum >> Plumbing Questions >> Can you have 'flow' without 'pressure'? https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl?num=1293630116 Message started by londonman on Dec 29^th, 2010, 1:41pm

Title: Can you have 'flow' without 'pressure'?
Post by londonman on Dec 29^th, 2010, 1:41pm

I don't think that you can however, part of the defence case for the builders merchants I am suing for damage caused by their Powerflush unit, is that a satisfactory pre-inspection test by them is to test the connections for tightness by pulling on them - because the unit works on 'flow' and not 'pressure'.

Sounds like bollocks to me.

Title: Re: Can you have 'flow' without 'pressure'?
Post by thescruff on Dec 29^th, 2010, 2:17pm

A heating pump, is actually a circulator, they work by displacing water in the circuit, however, there has to be a build up of pressure to move water from A to B.

There are several types of flushing kits, and you need to say what type you had, for example, as above a circulator displaces water, from A to B, but a flushing machine, takes water from C, pushes it down A and B goes back in the bucket, so it's not displacing water and a different kettle of fish.

A simple answer is yes there must be a build up of pressure, from the velocity.

Don't know if I can find a pic from years ago, but it shows a circulator with pressure gauges, and nearly 1bar differential between the inlet and outlet.

Title: Re: Can you have 'flow' without 'pressure'?
Post by londonman on Dec 29^th, 2010, 6:07pm

It was this one.

http://www.kamco.co.uk/cf30kit.htm

Connects into the ch system by removing the ch pump and replacing with the pipes from this unit. My understanding is that the pump in this unit will create pressure to push the water round the central heating system and then into the reservoir at the bottom.

Can you confirm that if say radiator A was flowing freely but when this was turned off and radiator B turned on (radiator B being very badly blocked) that the pressure in the system between the pump in the unit and radiator B flow would increase.

Title: Re: Can you have 'flow' without 'pressure'?
Post by CWatters on Dec 29^th, 2010, 11:42pm

You can't have flow without pressure but that's all a red herring.

The proper proceedure for testing the unit is detailed in the manual....

http://www.kamco.co.uk/GuidanceNotes/PDF/FlowCheck.pdf

Selected quote..

Quote:

8. Attach the pressure gauge into the hose end and turn the motor on for 30 seconds. While the motor is running you should get a reading of 19-21PSI

I would expect a hire center to use the manufacturers recommended test proceedure especially as..

Quote:

These are not time consuming, do not require a high level of expertise and will not invalidate the warranty.

No mention of testing connections by simply "pulling on them". Well ok it does say to check the connections as well but you know what I mean.

Title: Re: Can you have 'flow' without 'pressure'?
Post by thescruff on Dec 30^th, 2010, 1:22am

You should always open rad B before you close rad A.

Anyway you have the pressure from the pdf CWatters posted 19-21psi [smiley=thumbsup.gif]

Thats 1.38 bar ish which is about what I expected.

Title: Re: Can you have 'flow' without 'pressure'?
Post by londonman on Dec 30^th, 2010, 12:41pm

Thanks chaps.

Title: Re: Can you have 'flow' without 'pressure'?
Post by thescruff on Dec 30^th, 2010, 2:40pm

The problem you are likely to have is proving you did cause the hose to come off.

In my opinion you could be fighting a loosing battle.

Title: Re: Can you have 'flow' without 'pressure'?
Post by greg on Dec 31^st, 2010, 1:16pm

How did the hose come off? The hose threads onto the machine against a washer, so you'll get leakage from the connection, tighten up jobs a good un, or have they changed the way you connect the CF30 hoses, mine is about 4/5 years old now.