2 port and 3port motorised valves

[sr72]

hello all just trying to get my head around the above subject.it seems a little complicated!! are 3 ports usde for smaller houses and 2 for larger?whats the 3 tee rule? i bet it takes a bit of practice getting used to these.i understand the basics; 1 port for hw and the other for ch.wheres the best place to fit them?anybodys opinion would be appreciated if they reply.

 

[Kingsway]

There is no rule for port valves.U can use either a three port or two 2 ports
Normally three ports are used when no room stat is evident.

There are two types of three port. Mid position and diverter

i prefer two 2 port valves

 

[croydoncorgi]

The nice thing about 3-port valves is that they don't close - there is always at least one open path - inlet to A, inlet to B or inlet to both A & B. This means that you don't need a bypass for pump overrun whilst the boiler cools.

I do not understand the comment about lack of room stat. You can (and should) use a roomstat to control both 2 and 3 port valves.

 

[sr72]

thanks for the reply folks.just a couple of questions.in what circumstance would you fit a diverter in preference to a mid position or vice-versa? also what differenciates the 2,obviously ones got 2 outlets and the other 3.is there certain situations that you would fit one rather than the other.think i've just repeated the first question getting into a tangle now thanks up front if anybody can make sense of my messaage l

 

[swelec]

http://www.diyfaq.org.uk/plumbing/plumbingpage2.html#midposition

sorry to bring attention to another website, but there is a decent explanation here

 

[namsag]

22mm 3 port is usually ok for up to 8 normal sized rads above that 2 two ports are better as they are not as restrictive to the flow of water or use a 28mm 3 port..