Why can you not be told Benny Boy,
If a MOMO fails while in the open position, it is going to stay open.
If a spring return fails in the open position, there is a chance at least that it will return to closed.
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 engineersIf a closed valve might cause such risk, then there should be a requirement for additional safety to cover for such an event.
I suspect that Sunvic has changed its design to make it more attractive to installers. The wiring is now identical to the more common spring-return valves. Indeed, these MOMO valves now behave like spring-return valves, so there seems very little benefit in using them. The key benefit – that the valve stays where it is unless it gets a positive signal to move – has been lost. Of course, professional installers are the main market for manufacturers. Hobbyists on this forum, such as me, are a tiny market by comparison. I guess installers value simplicity so that they can diagnose problems quickly and recognise the wiring arrangements immediately. I assume therefore that Sunvic is trying to compete with the more common spring-return valves by making the installers’ lives easier and thus make it more likely that installers will recommend these actuators to their clients. A cynical view would be that installers care much less than their clients whether a valve and its actuator will last two or twenty years. They are also unlikely to be persuaded by engineering elegance over pragmatic simplicity.
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
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 )
View attachment 158673
View attachment 158674
how long have you had it in service?
lack of any proper bushing or bearings for the large wheel
I'd upgrade those reeds to digital output Hall sensors
reed tines becoming magnetised.
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