Three tee rule

[stratplus]

Can anyone explain this in simple terms perhaps with a diagram?

Read up from the John Reginald central heating book but without a diagram I'm non the wiser.

Does this only apply to "y" plans and anything to do with the 150mm between cold feed and vent from f+e cistern?

I know its the rule of thumb to prevent reverse circulation but tbh I don't understand it.

Fitted loads and normally common tee in a/c but doing alot of zoned heating now on both combi and un-vented systems so just wondering if it would make a difference where we joined all the returns.

 

[lame plumber]

reread Mr R and you might notice he is referring to open vent systems

 

[stratplus]

reread Mr R and you might notice he is
Silly question I suppose when:

"The 1st tee will be the open safety vent pipe connection"

On the return pipe it says the first tee will be the feed and expansion pipe connection but on the diagram and on other diagrams in other books shows the feed and expansion pipe filling on the return.
I have always been sent an airjec to use which prevents any of these issues happening I suppose.

 

[Roger Welton]

Isnt this how many cups you should have by 10am?

 

[Rickster123]

Isnt this how many cups you should have by 10am?

At the latest!

 

[gasmanrob]

Whenever you do the H, not that they are too common these days upgrade it and the joining piece between the tee's for example primary flow from boiler up in 22mm then fit 28mm tee carry up in 22 for expansion tee across in 28 to the next 28mm tee come down into the tee with your 15mm feed and carry out to the pump in 22mm that is a job well done!

 

[Killy Bing]

Pet hate is air separators......

 

[Simon F]

The book does have diagrams, and I thought it explained things in an easy to follow logic.
the picture with the 3 tee rule relates to older boilers with a low resistance to flow through them.

the next part refers to "boilers with a high resistance" - low water content,
the diagram shown there is the set up you are familiar with,
vent and fill together at neutral point. ( or an airjec )

 

[stratplus]

The book does have diagrams, and I thought it explained things in an easy to follow logic.
the picture with the 3 tee rule relates to older boilers with a low resistance to flow through them.

the next part refers to "boilers with a high resistance" - low water content,
the diagram shown there is the set up you are familiar with,
vent and fill together at neutral point. ( or an airjec )

Looked at it again and I understand it better now. The diagram with picture of cylinder is the set up im familiar with but that diagram isn't for the 3 tee rule (I dont think). It shows the cold fill into the flow and not return so contradicts the 3 tee rule.