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Old 20th Apr 2019, 8:59 am   #1
red16v
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Default Heat sinking grease?

I had to replace a small synchronous motor in a central heating valve yesterday*

When I took out the faulty motor I noted that it had some sort of 'grease' between the body of the motor and the metal chassis it was mounted on. I deduce this is some sort of grease to assist in heat transference between the motor and the chassis. I understand these valves, when operated by the central heating system, remain powered at all times when commanded to operate in the 'open' mode and therefore may get hot and hence this grease may assist in getting rid of some of the heat?

My question is - what sort of grease might this be? It looked like 'car grease', ie the sort of grease you might apply generally around a car. It wasn't the 'white' compound which is what I'm familiar with on transistor heat sinks etc. Any thoughts on what it might be and where I could obtain some?

*Seems to be a reasonably common problem with these sorts of valve. I tested the continuity of the winding (2.1k) as against the new one (2.3k). I had assumed the motor winding might have gone o/c or s/c but apparently not. Changing the motor brought it all back to life.
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Old 20th Apr 2019, 9:58 am   #2
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Default Re: Heat sinking grease?

I guess that any grease is better than none because grease is better thermally than an air gap. In the absence of anything better, I would use “car grease”, probably the high temperature 230 degree, lithium based LB10 stuff which was ubiquitous.
If you are buying, then I suggest heatsink compound though.

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Old 20th Apr 2019, 9:58 am   #3
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Default Re: Heat sinking grease?

They are synchronous motors and they often fail mechanically rather than electrically I found. As you say, they hold the valve open against the spring.
The grease could simply be gear grease that has melted and been drawn between the motor and plate by capillary action. I have never seen heat compound in one
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Old 20th Apr 2019, 12:45 pm   #4
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Default Re: Heat sinking grease?

I also suspect it's just standard (mechanical) grease, rather than a heat transfer type, but if you want certainty, you could try emailing Steve at http://www.seered.co.uk - I'm sure he'll be happy to tell you exactly what's used, and he probably even knows the valve concerned.

He looked at a Sunvic for me a few years ago, after I'd had to replace 3 in < 5 years.
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Old 20th Apr 2019, 1:01 pm   #5
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Default Re: Heat sinking grease?

Quote:
Originally Posted by Boater Sam View Post
They are synchronous motors and they often fail mechanically rather than electrically I found. As you say, they hold the valve open against the spring.
The grease could simply be gear grease that has melted and been drawn between the motor and plate by capillary action. I have never seen heat compound in one
Yes, no heatsink is needed. Motor
Valve
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Old 20th Apr 2019, 4:15 pm   #6
red16v
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Default Re: Heat sinking grease?

Quote:
Originally Posted by Goldie99 View Post
I also suspect it's just standard (mechanical) grease, rather than a heat transfer type, but if you want certainty, you could try emailing Steve at http://www.seered.co.uk - I'm sure he'll be happy to tell you exactly what's used, and he probably even knows the valve concerned.

He looked at a Sunvic for me a few years ago, after I'd had to replace 3 in < 5 years.
I might well do that, thanks.
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Old 20th Apr 2019, 4:19 pm   #7
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Default Re: Heat sinking grease?

Quote:
Originally Posted by Boater Sam View Post
They are synchronous motors and they often fail mechanically rather than electrically I found. As you say, they hold the valve open against the spring.
The grease could simply be gear grease that has melted and been drawn between the motor and plate by capillary action. I have never seen heat compound in one
It definitely looked like grease, looked look ‘classic’ car grease, perhaps a little thinner in consistency. I was impressed there was anything there at all to be honest! I have two other faulty valves, I guess I could them apart and have a look.
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Old 20th Apr 2019, 4:30 pm   #8
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Default Re: Heat sinking grease?

Quote:
Originally Posted by Julesomega View Post
Quote:
Originally Posted by Boater Sam View Post
They are synchronous motors and they often fail mechanically rather than electrically I found. As you say, they hold the valve open against the spring.
The grease could simply be gear grease that has melted and been drawn between the motor and plate by capillary action. I have never seen heat compound in one
Yes, no heatsink is needed. Motor
Valve
That motor appears identical to the one I bought from Screwfix to replace the faulty one. In the screwfix kit there are two ‘spare’ crimp connectors so you can cut off the spade connectors and crimp on the required ones. I bought 3 spare synchronous motors, a crimp tool altogether for £10 less than one complete replacement valve headset!

The valve it sits on is a 2 port valve by Siemens. The valve headset is held in place against the valve body by 4 clips/springs, you can apply firm pressure and release the two parts in situ - handy. But, Siemens know there are problems with these valves and our plumber replaced 2 out of 3 within months of our new installation at no expense to us. He said his firm had replaced many of these valves in the previous 12 months. Perhaps I will become the local expert, replacing the motor took less than 5 minutes and of course there is the satisfaction of a diy job well done!
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Old 21st Apr 2019, 6:13 pm   #9
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Default Re: Heat sinking grease?

If it's anything like the pair of 3-way valves in my heating, the motor is designed so that when powered it drives the valve to the required state and then stalls - though it's still powered.

In its stalled state it's still taking 5 Watts or so.

"Thermal grease" is cheap and easy to obtain - the silver-loaded stuff designed to go between PC CPUs and their heatsinks is good. At least in the heating-valve application you're not needing to worry about dielectric characteristics.
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Old 21st Apr 2019, 7:20 pm   #10
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Default Re: Heat sinking grease?

The motor is held in a stall in the middle position (both DHW and CH exits open) by a series diode. In DHW Only mode, the diode is bypassed and the motor run into a stall against the end stop.
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Old 24th May 2019, 7:57 pm   #11
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Default Re: Heat sinking grease?

Considering that this motor is mounted on the distribution valve, which itself is part of the pipework that is heated up by the boiler, isn't it more logical to insulate if from the heated pipework, rather than connect it to it thermally. Just a thought....
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Old 24th May 2019, 10:00 pm   #12
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Default Re: Heat sinking grease?

The grease is there as it 'melts' and oozes all over the place from the heat. A new valve won't have the grease there, just around the moving parts. I've just found a brand new one here and the original grease position can be seen. After a few years use the brass moving parts will be totally dry of any grease and the parts grind away at each other. This usually results in grinding a deep groove in the brass teeth of the pinion. Finally it gets to the point it no longer grips the rack that actuates the valve.
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Old 28th May 2019, 10:07 am   #13
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Default Re: Heat sinking grease?

Quote:
Originally Posted by matthewhouse View Post
The grease is there as it 'melts' and oozes all over the place from the heat. A new valve won't have the grease there, just around the moving parts. I've just found a brand new one here and the original grease position can be seen. After a few years use the brass moving parts will be totally dry of any grease and the parts grind away at each other. This usually results in grinding a deep groove in the brass teeth of the pinion. Finally it gets to the point it no longer grips the rack that actuates the valve.
Would a dollop of silicone grease help with this? Supposed to be non melting but no idea of its lubricity. Any tribologists about?
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Old 28th May 2019, 1:15 pm   #14
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Default Re: Heat sinking grease?

Quote:
Originally Posted by matthewhouse View Post
The grease is there as it 'melts' and oozes all over the place from the heat. A new valve won't have the grease there, just around the moving parts. I've just found a brand new one here and the original grease position can be seen. After a few years use the brass moving parts will be totally dry of any grease and the parts grind away at each other. This usually results in grinding a deep groove in the brass teeth of the pinion. Finally it gets to the point it no longer grips the rack that actuates the valve.
Ours is made by Tower and it replaced one made by Honeywell. I haven't opened the current one, but the curved rack-and-pinion gears are relatively easy to access. Perhaps a dollop of new grease every 12 months or so might be a good idea?
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Old 28th May 2019, 5:01 pm   #15
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Default Re: Heat sinking grease?

You could use a high melting point car grease. I have a tin of "Keenol" that I must have had for 30 years, but I don't know what the current equivalent is. HMP greases like Keenol incorporate a non-lubricating substance ( Bentonite?) that makes the oil component of the grease stay put. If the temperature gets too high, the oil will distill off, leaving the non-lubricating residue behind.

Thanks for the explanation of how these valves work. I did wonder if the three-position valves used the same motor as the two-position ones. I will have to have a look at our valve and see if it would benefit from a dollop of grease.
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Old 28th May 2019, 7:24 pm   #16
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Default Re: Heat sinking grease?

Maybe Copper Grease as used on brake parts would be ideal.
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Old 28th May 2019, 7:33 pm   #17
matthewhouse
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Default Re: Heat sinking grease?

I use copper/graphite grease all the time on threads to stop them seizing. I've always worried that the copper particles would be abrasive to moving parts. But I could be totally wrong, I'm not an engineer!
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Old 28th May 2019, 8:01 pm   #18
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Default Re: Heat sinking grease?

I think the particles would be so fine it would not matter.Those valves, divertor valves have quite a high failure rate I understand.
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Old 28th May 2019, 9:06 pm   #19
matthewhouse
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Default Re: Heat sinking grease?

The newer ones seem to have quite a short life. For a while a year or so ago were were replacing dozens of quite new actuator heads with mechanical problems, mostly the motor turning but the rack slipping. I've only ever replaced 3 failed motors though, 2 had gearbox faults, the other had winding failure. Which is why I had the spare to hand in my van!
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Old 29th May 2019, 9:51 am   #20
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Default Re: Heat sinking grease?

Our house is now around 4 years old, and we had to have both the 2*CH zone valves (complete head units not just the motors) replaced within 18 months. The heating engineer said Siemens knew they had a problem with them and we’re replacing them for free (but not labour of course! Luckily we were covered by our new house 2 year warranty). The engineer said their firm were replacing lots and lots of them and had a desk back in the office piled high with them. When I replaced the motor on one of the valves at the start of this thread I was concerned about the mating of the existing ‘rack’ with the new pinion on the new motor but it was fine and continues to be ok. I really don’t know what to say or think about greasing the rack and pinion mechanism - it would be quite difficult to do in situ I think, which is what I had to do to replace the motor).
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