Drayton ZA5 actuator head alternative
- Thread starter nickrw
- Start date
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Why the derogatory ?
I can be told and I listen.
Maybe the reason I cannot be told is that the information is not available.
However, do you agree that a momo is much more reliable in operation than a spring return? I believe the design is much better, much more robust and therefore much less likely to fail than is true of a spring return. The most likely failure mode is complete loss of power, which most likely would also affect the boiler too.
If a closed valve might cause such risk, then there should be a requirement for additional safety to cover for such an event.
its not a closed valve that causes the risk and yes there is an additional safety device to protect the cylinder if the first line fails, this is the reason that these should only be installed by G3 qualified engineers
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It seems that some "spring return valves" are mechanically a MoMo with the addition electrics inside the case of the actuator to make them appear to be spring return.
This is a public domain source that refers to this use of MoMo mechanics, makes good reading
https://www.automatedhome.co.uk/vbu...ise-of-motor-open-motor-close-valve-actuators
This is a public domain source that refers to this use of MoMo mechanics, makes good reading
https://www.automatedhome.co.uk/vbu...ise-of-motor-open-motor-close-valve-actuators
That discussion is in regards to 2-port valves.
As I have already suggested, I swapped out my spring return type Sunvic 3-ports, for a Sunvic momo. The momo reproduces exactly, the actions of the spring return version so it was an easy electrical swap, but the actual valve also needed to be changed too. The reason I decided to change was that I was fed up to the back teeth with the spring return versions failing. The failure modes were various, but often the motors would burn out, due to being constantly powered, the plastic parts would suffer from the internal heat and break or jam and the micro- switches would fail. The plastic part were under tremendous stress due to the spring + heat from the motor.
Such was the unreliability of the spring return, that I had planned to try to see if I could design something better and more robust, but then I came across the momo type, took a look and liked what I saw...
I spent ages bench testing one and investigating one, to see what it did and how it worked and found it to be quite a clever design. The motor is only powered to move the valve, unlike the spring return where the motor can be constantly powered to retain its position against the spring, via a resistor generating yet more heat. Unlike the item which Bernard quoted, my actuator/valve only moves when it is called to move - it motors to a called position, then stays there with or without power, until called to move to a new position. In summer, with no call for CH it will stay put in the HW position for the entire summer season. In winter, with only one call for HW per day, it will stay all day in the CH position. So there is zero internal heat generated in the actuator except for the few seconds whilst the motor changes the valve position. Because they only motor when required to, there is so much less wear and tear and they also save a few watts and a lot of heat degradation of the plastic parts.
The downside, is they are a little more complex electronically internally - http://www.seered.co.uk/sunvic_unishare_waterdamage.htm
explains the likely issues caused to these actuators by water damage. Probably these were mounted in other than an actuator up orientation to cause this damage. None of my actuators has suffered any water ingress in 35 years, despite the spring return actuator using the original valve for all of those years and of course it is mounted with the actuator uppermost. Who with any sense would mount an actuator which is reasonably water tight when installed uppermost, on its side or upside down anyway?
For what it is worth this is the actuator I designed for and use in the heating system in the cottage.
Operates on 12 volts. A magnet in the large gear wheel operates reed switches to (a) stop the power when the valve has reached the desired position and (b) create a status report back to the control system.
The status "Flowing" means the valve is fully open ( With hindsight "Full open" would have been a better label )
Operates on 12 volts. A magnet in the large gear wheel operates reed switches to (a) stop the power when the valve has reached the desired position and (b) create a status report back to the control system.
The status "Flowing" means the valve is fully open ( With hindsight "Full open" would have been a better label )
That is a quite impressive job Bernard, how long have you had it in service? The only part I would be critical of, is the lack of any proper bushing or bearings for the large wheel - that I could see.
Seven years.
The large wheel is located by the shaft of the valve and so far hasn't worn too much, but I do have spare wheels and PCBs for the next few decades
I had in mind for my version using a normal 240v actuator motor for drive, relays and Hall Effect switches. Basically, fully self contained so it could be a straight swap over for a normal actuator. Your version obviously needs an external 12v supply and some sort of relay interface board.
I have designed the controller ( based on a MicroChip PIC 18F2620 processor ) which drives the actuators directly.
The layout of this cottage needed a bit of lateral thinking to achieve a reasonably efficient heating and hot water system.
The layout of this cottage needed a bit of lateral thinking to achieve a reasonably efficient heating and hot water system.
I'd upgrade those reeds to digital output Hall sensors....a few boilers use reed sensing for DHW and primary flow, they suffer with the reed tines becoming magnetised. The Chaff Brittony goes into meltdown.
Like so many other regulations the G3 unvented regs are a shambles....open to wildly different interpretations and drawn up by those with little practical knowledge.
There are plenty of highly rated industry professionals that will happily disagree on the necessity to incorporate a 2 port spring return.
IMHO it is generally the cylinder manufacturers that have caused the argument by supplying a zone valve with their cylinders and then stating in their literature that it must be used..the guidance document G3 makes no such requirement...and indeed where low loss headers are utilised zone valves are not always necessary.
If you take a careful look at the classic wiring diagram supplied by most cylinder manufacturers you will see a serious flaw that actually defeats the whole 2 port argument and contravenes the G3 guidance document.
The non self resetting energy cutout (ie. the overheat stat) is generally wired in series with the normal cylinder temperature thermostat. Therefore when the zone valve fails to return to the closed position after the motor is de-energised (and this happens frequently due to broken return spring(s), a magnetised motor, sticking spindle gland O rings etc) the overheat stat is rendered redundant. The overheat stat should be wired in series with the zone valve microswitch feed to remain effective but of course the diagrams don't show this and the overheat stat terminals aren't always available for connection.
Another anomolly within G3 is the requirement that where a boiler is used as the heat source the energy cutout can be on the boiler but makes no mention of boilers that rely purely on thermistors for overheat shutdown. We've had boilers with no overheat thermostats for nearly 20 years.
Like so many other regulations the G3 unvented regs are a shambles....open to wildly different interpretations and drawn up by those with little practical knowledge.
There are plenty of highly rated industry professionals that will happily disagree on the necessity to incorporate a 2 port spring return.
IMHO it is generally the cylinder manufacturers that have caused the argument by supplying a zone valve with their cylinders and then stating in their literature that it must be used..the guidance document G3 makes no such requirement...and indeed where low loss headers are utilised zone valves are not always necessary.
If you take a careful look at the classic wiring diagram supplied by most cylinder manufacturers you will see a serious flaw that actually defeats the whole 2 port argument and contravenes the G3 guidance document.
The non self resetting energy cutout (ie. the overheat stat) is generally wired in series with the normal cylinder temperature thermostat. Therefore when the zone valve fails to return to the closed position after the motor is de-energised (and this happens frequently due to broken return spring(s), a magnetised motor, sticking spindle gland O rings etc) the overheat stat is rendered redundant. The overheat stat should be wired in series with the zone valve microswitch feed to remain effective but of course the diagrams don't show this and the overheat stat terminals aren't always available for connection.
Another anomolly within G3 is the requirement that where a boiler is used as the heat source the energy cutout can be on the boiler but makes no mention of boilers that rely purely on thermistors for overheat shutdown. We've had boilers with no overheat thermostats for nearly 20 years.
Control circuit voltage for a G3 installation should be linked through the unvented cylinders OH stat, in doing so would remove voltage to control circuit should an overheat condition arise, in this case the use of MOMO valves/spring return valves/mid-position valves (Y plan) would be a moot point.
I had considered alternatives to reeds, either photo or hall effect, but reeds were the simplist to impliment. BUT I did have to add magnetic shunts to prevent the reed from operating until the magnet was alongside the reed.
I have vague recollections of that but in the millions of reed switches ( relays ) used in telephone switching I do not recall a stuck reed other than welded contacts due to a fault elsewhere causing the reed to switch excessive current.
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