Flexihose Restrictions

[hilti68]

Hello again,

Just a question that popped into my head today whilst thinking about how to avoid work ......

I'm fairly new to the boards and have spent much of the past few days reading a lot of the other posts & replies, especially as regards isolation valves and fittings for a bathroom (my current project)

Opinion seems divided about the use of Flexihoses

I can see what some people say about the fact that, say, on a 15mm flexihose the nominal bore of the plastic pipe is only about 9 mm and hence this could cause flow &/or pressure reduction ....

... however, it occured to me today that even if I use fully soldered connections - either Yorkshire or end feed - and fit an isolation valve in-line on the supplies to basin, CW bath & toilet cistern - the internal diameter of the ball in the valve is only about 8mm anyway !

Or, put another way : The diameter of the opening of a ball islation valve is smaller than the bore of a flexible hose [ yes , I've measured them both]

I can't understand why the general opinion is that fitting the former [ie, isolation valves] is good practice & is recommended, which I planned on doing anyway & agree with; yet flexihoses are shunned;even though their I/D is less than the valve bore of an iso valve ????

Can anyone explain.

And yes, I am pedantic And maybe I also think about things too much .....

 

[TicklyT]

Think of the friction between the water and the pipe wall. The smaller the bore, the faster the water has to flow through it, so the greater the friction losses. Smaller bore pipes have a larger surface area to cross-section area ratio, increasing the friction, and the longer the restriction, the greater the losses.
An isolation valve has a bore restriction over a length of about 30mm, and a flexi. is about 300mm.

There are full bore iso. valves available if the losses through the valve are significant, say, on a gravity system.
On a mains pressure system it may be less significant, as there is more pressure to spare in the first place.

Then there is the matter of the life expectancy of the materials in the flexi. versus copper...