Two port zone valve on cylinder return

[stratplus]

Come across some of these recently, usually only ever see them on the flow to the cylinder, not on the return from it.
Any reason for this? Does it make any difference as still won't be any flow unless there is a call from the cylinder stat?

 

[dancinplumba]

On flow stops gravity

 

[Ermintrude]

Was told it prevents / reduices hammer

 

[stratplus]

Fully pumped systems though..

 

[dancinplumba]

Mean stop convection, flow hot and heating cylinder

 

[stevetheplumber]

usually found this way on gravity systems leaves the path to the cold feed and vent open

 

[stratplus]

Have you ever seen the flow go into the bottom of the coil? 2 port on flow pipe but to the bottom of the coil into the cylinder? Think some heat pump cylinders do this, Calorex cylinders?

 

[Best]

Have you ever seen the flow go into the bottom of the coil? 2 port on flow pipe but to the bottom of the coil into the cylinder? Think some heat pump cylinders do this, Calorex cylinders?

Yes, some recommend joining the flow to the bottom of coil. Telford unvented units have to be done this way. As long as it is pumped supply it won't matter.
I have always understood that the reason the flow should go to bottom connection is heat transfer will be quicker that way because the lower water in cylinder will be colder & the overall heat up time for the entire cylinder will be therefore faster.