Diverter valve actuator problems

[Surefire]

Hi chaps
Opinions please. I'm fed up of having to replace the head on the diverter valve on my heating system (Myson ACT322) every couple of years now. It gets stuck at various positions and causes really hot water in the hot tank or failure of the rads to warm up. A jiggle of the manual lever usually unsticks it but it's only temporarily. So I was thinking if installing an additional solenoid valve just to open and close the flow to the hot water tank. Being a sparky I should be able to install it electrically without problems. Just wondering if this it a good option or not. Or should I just keep buying new head units every 2-3 years. By the way, I've checked the mechanics of the valve itself and it doesn't seem overly stiff or hard to turn. I just think the quality of the replacement units isn't great. The original one lasted over 10 years.

 

[Agile]

You need to see why it is failing.

There are two causes, the motor winding goes open circuit [ Or rarely seizes up ]

Or the gears jam up.

You can spray a good aerosol lubricant on the gears at the annual maintenance.

Or you can just change the synchron motor if that is failing.

It sounds to me as if the valve is perhaps overheating. They are designed to operate in the open for cooling and NOT to get covered by clothes or insulation.

 

[oldbuffer]

If you have the space, ability and tools, I'd change from a Y plan (1 x 3 port motorised valve) to an S plan (2 x 2 port motorised valves), and use Honeywell valves. As above, make sure the valves are reasonably well ventilated.

 

[Harry Bloomfield]

I had similar issues with our spring return actuator, so many times, I took to repairing them and always having a spare in stock ready to fit. Understanding heat internal heat generation was part of the problem, I even tried adding a plate under the actuator, to divert heat from the pipework and drilling vent holes in the actuator, which seemed to help a little.

I was even considering designing a none-spring version myself, that is until I realised it had already been done commercially. A MOMO (Motor On, Motor off) actuator doesn't use a coil spring, nor does it leave the motor on/stalled to retain the valve position. The whole unit is under much less mechanical stress, because there is no spring involved.

Instead of running back and fourth a fraction of a turn, the MOMO works by rotating the valve spindle in only one direction, doing complete rotations from position to position. They are slightly more complex electrically, internally and tend to suffer water damage if not mounted actuator uppermost, but they have potential to be far more reliable than the spring return versions. Because the motor is unpowered once it has moved to the required position, they consume zero current.

Electrically, they are a direct swap for the spring return type, but the actual water valve would need to be swapped along with the actuator.

 

[Agile]

Yes, but MOMO valves have virtually disappeared from current useage.

I can only assume because they were so unreliable even though the idea behind the design seems a better one!

 

[Harry Bloomfield]

Yes, but MOMO valves have virtually disappeared from current useage.

I can only assume because they were so unreliable even though the idea behind the design seems a better one!

Maybe, because the were more complex, more expensive, they are not normally specified, but they certainly remain to be available. I did research them, before taking the plunge and the only common failure mode seemed to be that of water getting into the head. Swapping failed spring return 3-port actuators became a near annul task here, after suffering giving it a clout a few times when it had stuck. Not a definitive test period yet, but it has been troublefree for 3 years, since swapping to a MOMO. Despite this, I did buy a second one as a ready to fit spare

 

[Surefire]

Thanks for the replies folks. I'm pretty sure the problem is heat related. It sits in the airing cupboard and it gets pretty hot. Short of leaving the door wide open there's no other way of keeping it cool. I've ordered another one anyway and when it comes I'll have a go at lubing up the original with silicon spray. It'll kill or cure it. I've tried to fix them before with little success, they ain't really designed to be repaired. Come the summer I might look into changing it for a different type as suggested.

 

[Agile]

It is odd that that failure of the water seal is one aspect of the mid point valves which very rarely ever fail on any of the several makes.

Perhaps there are hardly any MOMO valves still made and they can manage with an unreliable water seal because they just supply a small market of replacing existing MOMOs where the limited life benefits them from early replacement.

Manufacturers cannot exist for ever if their products have unlimited lifetimes!

 

[Harry Bloomfield]

It is odd that that failure of the water seal is one aspect of the mid point valves which very rarely ever fail on any of the several makes.

Perhaps there are hardly any MOMO valves still made and they can manage with an unreliable water seal because they just supply a small market of replacing existing MOMOs where the limited life benefits them from early replacement.

Manufacturers cannot exist for ever if their products have unlimited lifetimes!

Good point! Our original valve had never had a problem with the spindle leaking, despite being 40 years old. The MOMO's as said are a little more susceptible to water, but leaks can be from more than just the valve spindle. Mounted head uppermost, the electronics are reasonably well protected from water.