To bend or to elbow?

[PM]

For a pumped CH system, is it better (where clearance allows) to bend pipes than to use soldered couplers?

Ta

Pete

[The3rd Earl Of Derby]

Where its permissable its always best to bend rather than joint, the less joints you have the less chance of an upset later. ;-)

-- Sir Benjamin Middlethwaite

[Christian McArdle]

It is always best to bend rather then elbow if it is possible. This applies to any plumbing system. It reduces flow resistance and noise.

Christian.

[The3rd Earl Of Derby]

I'm confused?

-- Sir Benjamin Middlethwaite

[Christian McArdle]

How so?

Christian.

[Steve Walker]

turbulence, presumably.

[The3rd Earl Of Derby]

How you can say using elbows restricts flow rate and causes noise in the system?

When the pipe is butted up into the elbow it makes contact with the ridge in the elbow and is a perfect join providing the solder has made a good airless joint.

-- Sir Benjamin Middlethwaite

[Broadback]

Can you drive faster and smoother round a sharp or wide bend?

[The3rd Earl Of Derby]

Thats irrelevent to the question.

-- Sir Benjamin Middlethwaite

[Christian McArdle]

There are several noises associated.

1. The rapid change of direction of the water when using high flow rates causes a hissing noise as there is lots of turbulence. A gradual bend does not upset the flow of water or invoke turbulence.
2. When there is a rapid change in flow rate, such as when a modern tap or toilet valve shuts off, the elbow gives a bigger jolt to the length of pipework, so often makes louder bangings or scrapings, particularly when the pipework is not firmly attached. A gradual bend doesn't provide any local obstruction for a hammer to act against. The gradual bend can also flex slightly, disipating any energy that does get expressed.

Christian.

[Chris Bacon]

Because it does! Use swept bends.

[Mark]

i have noticed this

-

[Christian McArdle]

If you point a hosepipe at the bottom of a wall, it splatters all over the place. If you point a hosepipe at the bottom of a wall with a nicely curved up former at the bottom, the water will bend round and rise upwards without anywhere near as much splattering. The same happens within the pipework. Although the splattering can't escape the pipe, it can make a lot of noise and will have more pressure loss.

Christian.

[The3rd Earl Of Derby]

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.

-- Sir Benjamin Middlethwaite

[The3rd Earl Of Derby]

Go find you're snorkel gear.

-- Sir Benjamin Middlethwaite

[Mungo]

Bends are better.

I've just bought the 15/22mm pipe bending tool from toolstation (

) and although at first it feels like trying to put an octopus into a tank (protrusions going everywhere) the finished job looks pretty nifty.

Admittedly, I won't use the tool every day, but it's still a neat bit of kit!

Mungo

[nightjar]

However, that is entirely irrelevant. Elbows cause the fluid to change direction much more abruptly than bends, which is what causes the restriction in flow. The larger the bend radius the better, with the best being a bend of infinite radius: i.e. a straight pipe.

Colin Bignell

[Christian McArdle]

Except that a bend made in a pipe with a pipe bender will be a flowed bend, whilst an elbow fitting will be a sharp 90 degrees. You can get some of the benefit of a flowed bend by using two 45 degree elbows with a short length of pipe between. Two 45 elbows are much better than one 90 degree.

Christian.

[Christian McArdle]

Yes, I wouldn't dream of using copper pipe without a bender handy. With a bit of forethought (and a small dent on the pipe) you can made 180 degree bends, too!

Christian.

[Chris Bacon]

There's a nice little table[1] ("Table 4: resistance to the flow of fittings, etc as equivalent lengths of straight tube") at:

pipe length, 15mm capilliary elbow = 0.37m compression 0.6 m swept bend 0.13m

AFAIR the maximum flow rate recommended is about two metres per second.

[1] They can't spell "metres", though.