To bend or to elbow?

[Harry Bloomfield]

The3rd Earl Of Derby formulated the question :

No they will not. The sharper the turn that the water has to make, the greater will be the resistance to that flow.

[The3rd Earl Of Derby]

Their both at 90deg, dick

-- Sir Benjamin Middlethwaite

[Christian McArdle]

You seem to assume that a 90 degree turn has a fixed efficiency. This is not so. A sharp 90 degree turn, such as that provided by an elbow fitting, is less efficient than a gentle 90 degree turn, such as that provided by a pipe bender (or formed plastic pipework).

Christian.

[Harry Bloomfield]

The3rd Earl Of Derby explained :

My name is not Dick. The angle may be the same, but one causes a very rapid change in direction of flow, presenting a face at 90 deg to the flow - whilst the other has a more gentle change. The resistance to flow of the latter is much lower be it gases, fluids or even solids. It might help to think in terms of trying to get grains of dry sand to flow down and around the elbow compared to the same through the bend. The latter would be just about possible, but the prior impossible.

Another way to explain it would be to consider pushing wires down a tube at an elbow versus towards a bend. There is no way to push wires past an elbow without a removable cover, though it is possible using a bend - even two or three at a pinch in series.

[PM]

This was the main point of my question - the radius of the bend in, say,

22mm pipe made with a pipe bender is much more than when joined by an elbow . I can picture in my mind this having an effect in fast-flowing situations, however would the effect be big enough in a pumped CH system to be worth worrying about?

[Dave Fawthrop]

|The3rd Earl Of Derby formulated the question : |> Ok maybe I have not made it clear so...I'm talking about a bend in a pipe |> at 90deg and fitting an elbow which is 90deg both will give the same flow |> rate. | |No they will not. The sharper the turn that the water has to make, the |greater will be the resistance to that flow.

How does the drop across elbow compare with the head available from a run of the mill central heating pump?

[PM]

I tried bending 22mm with a bending spring. Could only just bend it enough to make the pipe wobble when rolled. Got a pipe bender now - easy peasy!

[Harry Bloomfield]

Christian McArdle used his keyboard to write :

Even a perfectly straight pipe has resistance to flow. Compare the difference between the flow out of a short garden hose versus a long one.

[Chris Bacon]

If you've a lot of elbows in the system it will make a difference.

[Chris Bacon]

If you anneal the pipe first, it's easy to bend with a spring, but...

These do make it easy. A still spring has uses, though.

[TheScullster]

Another key advantage of swept/pulled bends is that they are less likely to form a settling point for crud. Having inherited a neglected 1970s installation with enough magnetite to block some recently installed (not by me) plastic pipe, I know that every little bit helps in flushing/cleaning operations. The reduced resistance to flow in a swept bend will not just aid water flow, but will also help crud to drain away too!

Phil

[Doctor Drivel]

Crud collects at the inserts of plastic piping, another poor point of this system. There is a gap between the inside pipe wall and the insert. This is the chamfer to aid slipping on the pipe.

[Calvin]

I hate to complicate things but it used to be possible to buy swept 90 degree elbow fittings which were a bit more expensive than the normal sort but really useful for maintaining flow rates and keeping the noise down. Unless plumbing has been dumbed down in the same way as other things recently it probably still is.

[Mungo]

I've decided to add three radiators to my new conservatory to try and even out the heat on chilly days. The heating comes to the conservatory via a pair of 15mm copper pipes (flow and return). I'd like to fan out from this pipe to the three radiators but would love there to be some sort of Y copper fitting instead of a T so that the flowing water isn't suddenly asked to turn 90 degrees abruptly. Something in the back of my head seems to remember that such fittings can be obtained, but I've resigned myself to believing that I am havering once again. So does anyone manufacture 15mm copper Y fittings?

Mungo

[Calvin]

I've certainly seen swept Ts in the past. They're not quite the same as a Y fitting but are probably more useful in your situation as you probably want one pipe to go straight on with a branch off for the rad. Our good friend Google came up with at least one manufacturer "IPB Conex", whoever they are. Try Googling for "15mm swept tee" or "15mm swept T".

[nightjar]

I've not seen one. However, another way to minimise the problem would be to reduce the rate of water flow where the water branches off. That could be achieved by stepping up to 22mm, putting in your branches, then stepping back down to 15mm.

Colin Bignell

[Dave Fawthrop]

| |Calvin wrote: | |> I hate to complicate things but it used to be possible to buy swept 90 |> degree elbow fittings which were a bit more expensive than the normal |> sort but really useful for maintaining flow rates and keeping the noise |> down. | |I've decided to add three radiators to my new conservatory to try and |even |out the heat on chilly days. |The heating comes to the conservatory via a pair of 15mm copper pipes |(flow and return). |I'd like to fan out from this pipe to the three radiators but would |love there to |be some sort of Y copper fitting instead of a T so that the flowing |water |isn't suddenly asked to turn 90 degrees abruptly. |Something in the back of my head seems to remember that such fittings |can be obtained, but I've resigned myself to believing that I am |havering once |again. |So does anyone manufacture 15mm copper Y fittings?

The sheds only stock Ts. I have never seen a Y fitting. As your system is almost certainly pumped, the head loss in a T is very small compared with the available head of the pump.

[Capitol]

Dave Fawthrop wrote: As your system

Worst case on a 15mm T for right angle change of direction is about equivalent to 4' of pipe run in copper/steel but 7' in plastic.

Regards Capitol

[Dave Fawthrop]

| | |Dave Fawthrop wrote: | As your system |> is almost certainly pumped, the head loss in a T is very small compared |> with the available head of the pump. | | Worst case on a 15mm T for right angle change of direction is about |equivalent to 4' of pipe run in copper/steel but 7' in plastic.

Thanks! colloquially two thirds of knack all.