The Problem
The 2-port valve and Mo-Mo Actuator on my Central Heating system often stick when moving between the “open” and “closed” positions.
[Actually, the actuator doesn’t stall – it simply clicks as the gears jump when there isn’t enough torque to turn the valve shaft.]
System description and History
Uses a Sunvic 2-port valve type ML3501 driven by a Sunvic SM5203 (5-wire) actuator, to turn the Central Heating (CH) on or off. Hot Water (HW) is not controlled – the HW cylinder is heated whenever the boiler is on. Note that the valve is sized for 1-inch inside-diameter pipework – not quite compatible with the modern 28mm outside-diameter pipe size.
The system was originally installed circa 1979 as an open system with a separate header tank, one Satchwell motorised valve and with gravity HW circulation. After a few months, the pipework was re-jigged (using the same valve) so that the pump now drives the water round both CH and HW circuits.
The boiler was replaced (maybe 10 years ago). At this time, the separate header tank was removed and the system changed to a closed one with a pressure vessel.
At around this time (maybe earlier), the original Satchwell valve and actuator were replaced with the Sunvic models described above. I still possess the old valve, but not the old actuator.
Observations
With the actuator separated from the valve, its shaft turns through the 90 degrees between the “open” and “closed” positions in 50 seconds. I’m moderately sure that the old actuator took longer than that – i.e. that it was lower-geared, and so had a greater output torque. I can rotate the valve shaft easily with my fingers, with no obvious point of increased resistance.
At one point I improvised a DIY actuator, using a “Drayton Replacement Synchronous Motor 230V 27010BQ” from B&Q, a gear train, a cam wheel and some microswitches. This was very low-geared, taking 300 seconds to move between positions. It was 100% reliable, but ugly, and I want to find a professional device that works.
The valve plate actually says “use with actuator type SZ” – but as far as I can see, all the “SZ” actuators available are of the “Motor on – spring return” type.
Questions
1. Can anyone recommend a Mo-Mo actuator with sufficiently great torque to operate my [relatively large diameter] valve ? If need be, I could make an adaptor plate to fit the actuator to the valve base.
2. I assume that I could in theory use a spring-return type actuator – all the other wires would be the same but there just wouldn’t be any wire to connect to “CH off”. But wouldn’t this require double the torque from the motor, since it would need not only to turn the valve but also to wind up the spring ? And can I be sure that the wound spring would have enough torque ?
3. Any other ideas ? I want at all costs to avoid having to drain the system.
The 2-port valve and Mo-Mo Actuator on my Central Heating system often stick when moving between the “open” and “closed” positions.
[Actually, the actuator doesn’t stall – it simply clicks as the gears jump when there isn’t enough torque to turn the valve shaft.]
System description and History
Uses a Sunvic 2-port valve type ML3501 driven by a Sunvic SM5203 (5-wire) actuator, to turn the Central Heating (CH) on or off. Hot Water (HW) is not controlled – the HW cylinder is heated whenever the boiler is on. Note that the valve is sized for 1-inch inside-diameter pipework – not quite compatible with the modern 28mm outside-diameter pipe size.
The system was originally installed circa 1979 as an open system with a separate header tank, one Satchwell motorised valve and with gravity HW circulation. After a few months, the pipework was re-jigged (using the same valve) so that the pump now drives the water round both CH and HW circuits.
The boiler was replaced (maybe 10 years ago). At this time, the separate header tank was removed and the system changed to a closed one with a pressure vessel.
At around this time (maybe earlier), the original Satchwell valve and actuator were replaced with the Sunvic models described above. I still possess the old valve, but not the old actuator.
Observations
With the actuator separated from the valve, its shaft turns through the 90 degrees between the “open” and “closed” positions in 50 seconds. I’m moderately sure that the old actuator took longer than that – i.e. that it was lower-geared, and so had a greater output torque. I can rotate the valve shaft easily with my fingers, with no obvious point of increased resistance.
At one point I improvised a DIY actuator, using a “Drayton Replacement Synchronous Motor 230V 27010BQ” from B&Q, a gear train, a cam wheel and some microswitches. This was very low-geared, taking 300 seconds to move between positions. It was 100% reliable, but ugly, and I want to find a professional device that works.
The valve plate actually says “use with actuator type SZ” – but as far as I can see, all the “SZ” actuators available are of the “Motor on – spring return” type.
Questions
1. Can anyone recommend a Mo-Mo actuator with sufficiently great torque to operate my [relatively large diameter] valve ? If need be, I could make an adaptor plate to fit the actuator to the valve base.
2. I assume that I could in theory use a spring-return type actuator – all the other wires would be the same but there just wouldn’t be any wire to connect to “CH off”. But wouldn’t this require double the torque from the motor, since it would need not only to turn the valve but also to wind up the spring ? And can I be sure that the wound spring would have enough torque ?
3. Any other ideas ? I want at all costs to avoid having to drain the system.
