need to add info about
- differences in wiring of spring-return & non-spring valves
- how 3-port mid-position valves work
Re the orange picture, it took me some puzzling to work out what it was, a text label would really help. NT 08:01, 10 January 2007 (GMT)
But there _is_ a text label under the picture - ?
--John Stumbles 19:15, 10 January 2007 (GMT)
I think the reference to Hydronic wrt a 3 way valve is a spelling mistake perhaps you mean hydraulic, certainly it doesnt make any technical sense as its the tradename if the Smiths fan assisted plinth heater (a finned coil with axial blower)
The original Honeywell spring return 3 way valve with mid position was a curiously convoluted solution which has been shrouded in mystery untill the description provided (tkx btw) - personally as a professional engineer i hate it aand regard it as a nasty bodge. But a million homes probably still have this device in their Y plan systems.
I think it worthwhile to discuss the earlier system where a TRV was installed on the outlet of the HW heating coil to give a praticular DHW temperature.
As I recall - some 30 years ago - there was no zone valve and I think the pump only came on when CH was demanded and only pumped through the radiators. The HW tank was mounted above the boiler and the heating coil was gravity circulated and had 28mm tubes
- Good point - that might fit well in this section on C Plan systems. IIRC there was a popular valve often used for this with a trade name that I forget - something like silitron valve or something like that? --John Rumm 03:15, 13 October 2010 (BST)
The controller (similar to the Honeywell st699 but and earlier model?) had a mechanical interlock on the sliders controling CH and HW.
you could have
All off HW on 1x 2x HW + CH on 1x 2x
CH on by itself
Come to think of it, I dont remember a HW coil bypass gate valve being fitted (not very kind to the boiler (a potterton 40,000 Btu model) but I dont remeber any operating problems.
Obsolete Drayton valve
Interesting discovery. I'm curious who is User:A_tranter?
I've removed the comparison with the Sunvic electronic MOMO which seems spurious since the Drayton under discussion is not - unlike the modern Sunvic MOMO - a drop-in replacement for the 'standard' Honeywell-etc mid-position valve (the standard type requires CH CALL and HW CALL and SAT, whereas the Drayton seems to want CH CALL and SAT and HW CALL). In this respect, clever as the Drayton may be, the old blue Switchmaster is more compatible with current systems.
I've also changed the text describing the bullet-point list to be that it's a list of features, not of advantages of this valve over modern designs, since some of the listed points (e.g. the plastic cam) are actually disadvantages! Likewise the claim that the discontinuation of this design was the result of a conspiracy withing the heating controls industry to eliminate longer-lived designs. (I'm not saying that isn't the effect of the move to spring-return valves, but there's no evidence for the conspiracy theory and there's a sort of Occam's Razor rule that where something could be conspiracy or cock-up it's generally the latter!)
YAPH 20:13, 6 December 2010 (UTC)