2 way valve info ?

[vectraguy]

Hello all, I need some info about a motorised 2 way valve which is going to be used for a non central heating application.

My question is, when the motor is energised and the valve either closes or opens (depending on the type) does the motor remain energised even though the the job is complete, and the return spring can only work when the current is switched off.

If that is so wouldn't the motor become hot by not being able to turn, or is there an internal micro switch that cuts of the 240volt supply at the end of it's travel, but thinking about it that would allow the spring to do it's job when the valve need to stay open or closed.

any info appreciated

Regards vectraguy

 

[45yearsagasman]

Yes on spring return valves the motor remains energised.Motor open motor close valves do not remain energised.Consider using one of those.The reason synchron motors fail is that they remain energised.

 

[vectraguy]

Yes on spring return valves the motor remains energised.Motor open motor close valves do not remain energised.Consider using one of those.The reason synchron motors fail is that they remain energised.

Thank you very much that's exactly what I wanted to hear m8 so I'l get a motor on / motor off type valve for the job, probably cost a bit more, but reliability is worth it.

Regards vectraguy

 

[Onetap]

Thank you very much that's exactly what I wanted to hear m8 so I'l get a motor on / motor off type valve for the job, probably cost a bit more, but reliability is worth it.

Regards vectraguy

SFAIK, Sunvic are the only makers of Mo-Mo valves aimed at the domestic market and their reliability is dubious.

http://www.seered.co.uk/sunvic.htm

I am not aware of any spring-return Mo-Mo valves. Honeywell zone valves are reliable, but the motor is continuously energized.

PS You can get actuators which contain rechargeable batteries that drive the valve to the fail safe position in the event of a power cut. As usual, these aren't made for domestic use and given the relatively short life of rechargeable batteries, is likely to require regular testing and replacement. An example is the Siemens SSC61.5 actuator, which has a 24V AC/DC power supply and a 0-10V control signal. It would be possible to drive the actuator to a fail-safe position from a separate 24V battery, if you can find a 24V dc actuator, but most commercial actuator motors require 24V ac.

 

[TicklyT]

I understood the valve motor is held against the return spring by a lower current than it's running current. The motors are designed with these operating conditions in mind, so they are not damaged by them. I believe they cut the mains power and apply a low power DC braking current via a limit switch to hold against the return spring.

 

[45yearsagasman]

I believe that is the case with mid position valves but not with 2 ports.I'll have to look closer at the internals of these valves.

 

[vectraguy]

I understood the valve motor is held against the return spring by a lower current than it's running current. The motors are designed with these operating conditions in mind, so they are not damaged by them. I believe they cut the mains power and apply a low power DC braking current via a limit switch to hold against the return spring.

Thanks for your comments, and I remember seeing ex wd equipment having electromagnetic relays on which the coil had three leads instead of the usual two.

I measured these with an ohmeter and found one common and one with the lowest resistance, and the other with a higher resistance.

Any inductance wether relay coil or motor windings always has an high mag inrush current at point of switch on, but once that has expired, and the motor is running, or the relay armature has reached the iron core it can be retained with a much lower current.

This is achieved by an external switch automatically connecting via the higher resistance connection, which in the case of a valve operating motor would considerably extend the operating life.

Obviously valve motors only have two connections so to reduce the coil current it would require a fixed resistance to be placed in series with the coil input but only after the motor had completed it's travel.

Certainly not impossible but a bit tricky.

Regards vectraguy.

 

[SeeRed]

As a scientist/engineer I mend quite a few of these as a hobby since first publishing my SeeRed webpages on Sunvic valves. The link is given above or just ask Google for SeeRed website + sunvic valves.

There are basically two types of domestic motorised valves - MoMo (motor on and motor off). These are in my view the best type if only because of the uniform motor torque available throughout the whole range of travel.

TWO PORT spring return use full motor voltage to stay in the open position and get warm, they eventually fail but often just because of an easily fixed microswitch problem. THREE PORT (mid position) use full motor voltage when fully open (central heat only) and reduced voltage (via diode and a resistor) when in mid position. These fail more often not because of motor failure but because at mid position full restore torque is not available and a sticky motor may not return reliably to the closed (dhw) position. Sunvic SD2701 and variants are notable here. They also have microswitch issues - again often easily fixed.

I am appalled by the number of actuators that are thrown away - when they can be mended for much less than the cost of a new actuator. This applies especially to the Sunvic MoMo design which is actually quite clever despite its design weakness, and is covered in my webpages. Sunvic 2301 and 2701 and variants are also thrown away in large numbers.

If any plumbers have a large box full of failed actuators I would be interested in obtaining these to see how many could be mended and to publicise this - as an aid to conservation and reducing waste.

Many householders pay over £100 to have an actuator replaced when often a £12 repair is all that is needed. Some installers replace programmers when it is just the motorised valve actuator that has an intermittent fault.

 

[SeeRed]

By the way, a spring return MoMo valve is a contradiction in terms - a valve actuator is EITHER spring return (usually motor open, spring close or occasionally, for failsafe reasons, motor close, spring open) OR it is a MoMo type.

A MoMo valve will stay in whatever position it was in when the power (or the motor) failed so cannot be inherently failsafe - as are the (very unusual) motor close spring open types. All assuming that the spring return mechanism is working OK!