Magnetic drive water pump failure

[MtB]

I've just spent the afternoon trying to clear what I thought was an air lock in the Whispergen heating circuit after draining and refilling it to add in the calorifer to the radiator circuit. The real fault turned out to be the (external) magnetic drive water pump I fitted has failed. It is a pump bought from ebay and sold as suitable for a Webasto/Eberspacher radiator circuit.

The motor runs fine but the odd thing is, the magnetic drive cup fitted to the motor shaft seems to be loose and not actually rigidly connected to the shaft. The motor shaft is a well machined and accurate fit into the metal bush in the centre cup but clearly not actually fixed to it. Consequently the motor shaft spins but I suspect the magnetic drive cup stays roughly stationary. 

Does anybody know if the drive cup is supposed to be fixed securely to the motor shaft?

Many thanks...

[Nickhlx]

Did it get too hot  at some recent point in time ?

"When heated above 176° Fahrenheit (80° Celsius), magnets will quickly lose their magnetic properties. The magnet will become permanently demagnetized if exposed to these temperatures for a certain length of time or heated at a significantly higher temperature (Curie temperature) "

Nick

[MtB]

On 28/10/2017 at 19:47, Nickhlx said:

Did it get too hot  at some recent point in time ?

"When heated above 176° Fahrenheit (80° Celsius), magnets will quickly lose their magnetic properties. The magnet will become permanently demagnetized if exposed to these temperatures for a certain length of time or heated at a significantly higher temperature (Curie temperature) "

Nick

 

Nope. The magnets are fine. One of them is not, as I said, securely fixed to the motor shaft. It appears to be designed that way. This seems very unlikely so I'm asking if anyone KNOWS whether is is supposed to be fixed securely to the motor shaft, or a close and accurate fit but free to spin on it, as mine actually is. 

[MtB]

Or alternatively, does anyone know where I can buy another 12v water circulating pump tomorrow (Sunday)? I'll have a look on the MC site and see if they stock them.

[Alan de Enfield]

3 minutes ago, Mike the Boilerman said:

Or alternatively, does anyone know where I can buy another 12v water circulating pump tomorrow (Sunday)? I'll have a look on the MC site and see if they stock them.

I know where there is one of these for sale if that any help. Can be posted Monday.

£80 or offers.

 

[MtB]

On 28/10/2017 at 20:02, Alan de Enfield said:

I know where there is one of these for sale if that any help. Can be posted Monday.

£80 or offers.

 

 

Thanks for the offer Alan.

Is it 12v or 24v?

What I actually have, and need, is one rather like this:

[Alan de Enfield]

2 minutes ago, Mike the Boilerman said:

 

Thanks for the offer Alan.

Is it 12v or 24v?

What I actually have, and need, is one rather like this:

OK - different beast completely.

[MoominPapa]

Moomin reminds self to tell the Bolin pump he loves it, and please don't break.

 

MP.

 

[nicknorman]

Yes, clearly the driving magnet must be fixed to the shaft. How else could it possibly work!?

what sort of flow rate do you need? I’ve found the pumps from Solarproject to be very good. And cheap. But they are quite small, 11l/min (with no restriction) max. They doma 24v version too(are you still on 24v?)

http://shop.solarproject.co.uk/catalog/product_info.php?cPath=2&products_id=10&osCsid=b3a60828fd6efd8de6bd0e7b33726eba

But obviously, not available tomorrow.

Edited October 28, 2017 by nicknorman

[MtB]

Thanks Nick. I need 6 litres a minute but that is against whatever hydraulic resistance is created by about 20m of 22mm tube. One of those pumps will probably be ok but I might get two and run them in series.

IF Aralditing the cup magnet onto the motor shaft tomorrow turns out to be a failure! 

[mross]

Loctite might work better if the clearance is very fine.  Or you could peen the shaft with a centre punch to create a press fit.

Edited October 28, 2017 by mross

[MtB]

On 28/10/2017 at 20:56, mross said:

Loctite might work better if the clearance is very fine.  Or you could peen the shaft with a centre punch to create a press fit.

 

You're right. Loctite is EXACTLY the right thing for the job!

I was already planning to have a go with a centre punch. I'd estimate the clearance is about 0.003".

[mross]

If you can get it to a machine shop it could be knurled.  I hope you have success.

[BEngo]

If not try uxbridge boat centre for a v similar Johnson circulating pump.

N

[MtB]

Ok, a few judicious centre punch as suggested by that nice Mr Oss did the trick. 

The very last indentation, closest to the motor shaft, is the one that made the difference. It changed the fit on the shaft from loose to interference. After carefully driving the magnetic cup onto the shaft it drives PERFECT!

Thanks for all the answers everyone. I'll buy one of those solar pumps as a backup for when it next fails!

 

[reg]

1 hour ago, Mike the Boilerman said:

Ok, a few judicious centre punch as suggested by that nice Mr Oss did the trick. 

The very last indentation, closest to the motor shaft, is the one that made the difference. It changed the fit on the shaft from loose to interference. After carefully driving the magnetic cup onto the shaft it drives PERFECT!

Thanks for all the answers everyone. I'll buy one of those solar pumps as a backup for when it next fails!

 

That's got to be hood news I've just checked the whispergen spare prices, can see why you would want to find an alternative £336 for a 12v pump. 

Eta

Just found this and  and can see why spares cost so much now 

http://www.cruisersforum.com/forums/archive/index.php/t-119884.html

 

Edited October 29, 2017 by reg

[MtB]

On 29/10/2017 at 15:29, reg said:

That's got to be hood news I've just checked the whispergen spare prices, can see why you would want to find an alternative £336 for a 12v pump. 

 

Fortunately this one wasn't a genuine Whispergen pump. It was still a decent quality pump (supposedly), and cost about a hundred quid on ebay. A very confusing fault though as the slip was intermittent, and all the time the motor ran with no discernible difference in sound between when it was pumping and when it wasn't. Probably why it was on ebay in the first place!

[Flyboy]

2 hours ago, Mike the Boilerman said:

 

Fortunately this one wasn't a genuine Whispergen pump. It was still a decent quality pump (supposedly), and cost about a hundred quid on ebay. A very confusing fault though as the slip was intermittent, and all the time the motor ran with no discernible difference in sound between when it was pumping and when it wasn't. Probably why it was on ebay in the first place!

I think you slightly misinterpreted Mr Oss's suggestion. I think he was suggesting peening the shaft to raise the metal and create an interference fit. Your way may work ok if you have used Loctite as well. Time will tell.

[WotEver]

7 minutes ago, Flyboy said:

I think you slightly misinterpreted Mr Oss's suggestion. I think he was suggesting peening the shaft to raise the metal and create an interference fit. Your way may work ok if you have used Loctite as well. Time will tell.

That’s how I understood the suggestion too and was surprised when I saw Mike’s photo. However, if it works...

[nicknorman]

10 minutes ago, WotEver said:

That’s how I understood the suggestion too and was surprised when I saw Mike’s photo. However, if it works...

I think it depends on the nature of the relevant materials. The shaft is probably very hard and might bend or break before it deforms significantly. Whereas the cup is clearly made of softer material.

[WotEver]

1 minute ago, nicknorman said:

I think it depends on the nature of the relevant materials. The shaft is probably very hard and might bend or break before it deforms significantly. Whereas the cup is clearly made of softer material.

A good point. I also thought afterwards that he may not have been able to access the shaft ‘side’. 

[Ex Brummie]

I bought from Amazon an XCsource pump for £14.99. High performance with good temperature rating. They are currently out of stock, cheapest I can now find is £67.

Just seen on Ebay for £22.95

Edited October 29, 2017 by Ex Brummie
looked harder for supply