2 port / mid position valves

[timhoward]

What is the failure mode of these units that are being replaced so soon? Are the motors open-circuit, shorted turns or just seized?

They are all Honeywell units bar this last one.
I've only investigated 2 of them and they were both open circuit.
This last Drayton one is yet to be examined but I will do asap.

 

[Lucien Nunes]

Your analysis of the operation of the two midpoint release scenarios is exactly right. It's worth mentioning that the key to the midpoint operation is that a permanent-magnet synchronous motor locks up against any attempt to rotate it when fed with DC, because one polarity of rotor poles is permanently attracted to the stator poles. The resistor limits the current which would otherwise be excessive as the inductive reactance of the motor is no longer part of its impedance on DC, only the resistance. But it is the unidirectional current, not the reduction of it, that causes it to stop dead.

The relay shown in the drawing would work although as I mentioned above, I would feed the relay coil from the programmer CH output. This means that once the water is heated, the valve will remain in the heating-only position until the end of the programmer period and then release back to the rest position. With the relay wired as he suggests above, the valve will be de-powered as soon as the room stat opens, causing the valve to make an unnecessary end-to-end travel for every cycle of the room stat. Apart from increasing wear on the valve, if the pump is on overrun it will inject a slug of hot water into the cylinder coil each time it does so.

 

[johntheo]

Your suggested mod looks very good, do the open circuit failures found by Tim, above, point to anything in your view?.
I know of one case, with solid fuel heating only, where a dump heat radiator mounted high up has a N/O Honeywell 2 port valve which has been energized (to keep it closed) 24/7 for the past 7/8 years or so and only opens in the event of power failure, the owner does test it frequently, be interesting to see its lifespan.

 

[PEG]

Your suggested mod looks very good, do the open circuit failures found by Tim, above, point to anything in your view?.
I know of one case, with solid fuel heating only, where a dump heat radiator mounted high up has a N/O Honeywell 2 port valve which has been energized (to keep it closed) 24/7 for the past 7/8 years or so and only opens in the event of power failure, the owner does test it frequently, be interesting to see its lifespan.

Hi,although not relevant to the topic,i feel i have to point out that a heat sink or dump radiator cannot be valved,either with a manual or electric valve.

This has probably been done,as a result of a poor design or incorrect pipework.

The mention of the customer testing it frequently,is an indication of their knowledge,of the above.

 

[Lucien Nunes]

I would infer that it is to dump heat in the event of a power outage stopping the circulating pump. It is described as mounted high-up (presumably for gravity circulation) and might not provide useful heating if left operational under normal conditions, hence the use of the normally-open valve held shut electrically.

 

[Simon47]

My only experience with these valves is at a mate's pad - and I've replaced two motors (actually, one motor and a head as it had other faults as well) in a few years. I would suggest that the best fix is to modify the pipework to 2off 2 port valves.
As to why people don't fit the relay as described above ... well that would a) cost time and money, and b) mean recognising that there's a problem. How many wetpants do you think actually understand these ? How many are happy to charge to keep replacing heads or motors ?

 

[johntheo]

If HW programme sector available user can just programme it to be last request before nightly ---- down, should help??

 

[Simon47]

But don't forget that normally the cylinder stat will have turned off the HW demand before the programmer does. So unless the occupier has a habit of using a decent amount of hot water late at night, after the heating has gone off, then the CH will usually be the last demand.

 

[johntheo]

So it won't just c/o to HW and sit there unless cylinder stat is also calling?

 

[brianmoooore]

If the cylinder stat has turned off before the programmer or the room stat switches off the heating, the valve will remain powered and in the heating position until either the power to the system is switched off for a short period or the programmer switches on the hot water and the cylinder stat has turned back on.

 

[PEG]

I would infer that it is to dump heat in the event of a power outage stopping the circulating pump. It is described as mounted high-up (presumably for gravity circulation) and might not provide useful heating if left operational under normal conditions, hence the use of the normally-open valve held shut electrically.

Yep,it's a familiar setting,with all described,as making sense....but it cannot be signed off as suitable for use,by a Hetas inspection,if required for any reason.

There are fundamental failures,in the described system. The Hetas accreditation has an extra module for wet systems,to allow installations to be checked as compliant.

The heat dump emitter is a safety addition,and whether or not it provides any functional heat,is secondary to it's inclusion,as a fail-safe part of the system. It is not valved,either by addition of manual or electric valves,deliberately,to prevent accidental or intentional non-operation.

The reason for all the above panic? ......is a solid fuelled boiler is most generally,an uncontrolled heat source,that is,whether it is 5,12 or 25Kw,it cannot be turned off instantly,as can a gas or electric device.

It just disregards any external faults,failures,power cuts or pumping,and continues inputting that heat in to the system,which by design,needs a means of dumping that heat,should all the other sinks (radiators,stored DHW,etc) be satisfied.

The means of dumping this excess heat,should never rely on valving or electrical power,as it needs to be permanently failsafe. The very fact that this thread begins with possible sticking electrical valving,is proof enough of the above reason.

The no valving,although much ignored,is there for a good reason. When these systems run in to flow issues,although open vented,the slowed or stalled water in the source,will kettle. This can be very dramatic,and sound like the end of the world,with vent pipes blowing the water out of header tanks,and such,but the banging and vibration will loosen all or any of the debris and scale,within the boiler and pipework.

This,with luck,will still make it through the pipework,but can form a blockage at any restriction,with any valve,even if open,providing an opportunity to choke.

The last part is even more dramatic,and has levelled many properties in the past.

It goes like this....blockage = steam build up = pressure increases/temp rises = standard copper/olives let go = release of pressure = heated water instantly flashes to steam 1600 times the volume,and kaboom.

The one and only reason i have painfully rattled on,is the thought that someone may trawl the web for solid fuelled info,and take a brief description of a system,as a blueprint for their own?

 

[johntheo]

If the cylinder stat has turned off before the programmer or the room stat switches off the heating, the valve will remain powered and in the heating position until either the power to the system is switched off for a short period or the programmer switches on the hot water and the cylinder stat has turned back on.

Yes, quite correct, had to look at the schematics of this ingenious but devilishly cunning device again.