Mag Drive and emptying tanks

[YungPlantEng]

Not used to mag drive pumps but if you’re looking at a small (3 hp) mag drive pump in batch operation where a tank and line gets emptied regularly, wouldn’t you have regular bearing failures regardless of the NSPH of the pump? This is a 3600 rpm pump for reference, but from my understanding if a pump is ran dry for 30 seconds and it’s a self cooled mag drive it’s going to fail. I can slap an amp guard on it and call it a day since it’s not run regularly, but was wondering what thoughts are on this. NSPH available is fine just by vapor pressure of the fluid. Silicon carbide bearings if that changes anything.

 

[TugboatEng]

Blackmer Magnes pump line is a solution to your problem. They tolerate dry running.

 

[TiCl4]

We do this all the time. Get pumps specifically designed for dry run.

To give you another manufacturer in addition to the above: We installed some Iwaki Sanwa pumps 2 years ago for this exact scenario. That, plus either flow/amp monitor for dry run indication, where we allow the pump the run 15 seconds after dry run indicator, should give good pump life. We are probably 700+ cycles in on these pumps with no issues.

 

[pierreick]

Hi,
Another reference

https://www.finishthompson.com/run-dry/

Pierre

 

[YungPlantEng]

Appreciate it guys. A project engineer was telling me that running it dry for 15 seconds each empty would cause damage relatively quickly but considering the size of the pump I’m not very concerned with it.

Interesting that the other poster mentioned blackmer pumps. We recently installed some regenerating turbine ones but have had some issues related to our dome loaded bypass valve (by blackmer) that maintains the discharge pressure - due to our application the backpressure of the discharge valve is pretty variable and impacts discharge pressure. Not sure if there are similar ideas to balanced bellows for dome loaded valves to guard against backpressure variability but if you have thoughts on that I’d appreciate it.

 

[MJCronin]

Relying on the technical expertise of a project engineer, eh ?..... Hmmmmmmmmmm...

MJCronin
Sr. Process Engineer

 

[TiCl4]

This isn't a plug for the below vendor, but in the link below they do mention some tests and results for dry running. This comes from a biased source, obviously, but it still provides additional information.

There does seem to be a correlation between magnet weight and dry-run capability, so larger mag-drive pumps would need closer scrutiny than, say, your small 3 HP pump.

Overall, just work with the vendor on your application. Based on these tests and my own experience, though, I'd still say that 15-30 seconds for whatever pump vendor you choose should be fine for dry-run as long as the pump was designed for dry-run.

https://magnatexpumps.com/dry-run-resistant-bearings.php

 

[EdStainless]

In my experience, ceramic on ceramic bearings don't need lubrication, they do need cooling.
When we were situations when dry run was possible we ran ceramic on WC.

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P.E. Metallurgy, consulting work welcomed