Pump seal

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ptonsparky

ptonsparky

Tom
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
How long of running dry does it take to ruin the seal on a centrifugal pump? Seconds, minutes, hours?
Customer with a large holding tank and a 100 hp pump that maintains pipeline pressure. The holding tank went dry and the pump ran for hours. I think a loss of pressure setting, 4-20ma input, on the VFD could have prevented the damage to the pump.

Obviously the controls of pump supplying water to the tank need repair.
 
I'm not sure what drive you're using but a Yaskawa IQPump can be set to fault if underloaded after a set time delay. It monitors current, so a field installed 4-20mA sensor or pressure switch is not required.

I have a Yaskawa set up on a 100HP manure booster pump fed from a tractor agipump pumping out of a lagoon that the customer wanted to fault in case he ever ran the tractor out of fuel and starved the booster.

The other brands we work with our ABB and AB, not sure if they have the same setting buried in their parameters.
 
Most drives can do that. But I think what Tom was saying is that IF they had a drive, it could have prevented this but they don’t now (yet).


I think the question on the seals can only be answered by the pump mfr. as mentioned, some can take (or claim) unlimited dry running time, such as Flygt submersibles. I’ve seen others fail within minutes, ie those that require a separate clean water source for the bearings. I learned that one the hard way, stating up a 600HP vertical turbine pump without checking with the pump guy. I had to buy the bearings.
 
Jraef said:
Most drives can do that. But I think what Tom was saying is that IF they had a drive, it could have prevented this but they don’t now (yet).
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Might be easy to do if there is a drive being used, but certainly have all sorts of things to control basic magnetic motor starter as well. Limit switches (float, pressure, maybe even temparature, etc.), conductivity sensing relays, current sensing relays, photo sensors, proximity sensors all have possibilities here.
 
As others have said, it depends on the seal materials. For example, I have never seen one fail on a Flygt pump but then I don't normally run them dry. Their seals are tungsten carbide, or sometimes silicon carbide. A far cry from your average Bell & Gossett ceramic seal.

Failure of a mechanical seal shouldn't cause a pump to fail to work nor damage the pump. It simply amounts to a leak external to the pump. In some situations, where the suction side of the pump is at a vacuum, it can cause a loss of prime, and that can harm the pump.

As far as "dry running protection".....you basically have your choice of measuring suction pressure, discharge pressure, or water level in the supply tank. You can do it with current measurement but it wouldn't be my first choice.
 
Also, I doubt if it ran truely dry the whole time, compared to fresh out of the box never filled w/ water.
 
Barbqranch said:
Also, I doubt if it ran truely dry the whole time, compared to fresh out of the box never filled w/ water.
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Very true. The seal was fine, no leaks Noise was from something else.

It should fault and stop now if pressure drops too low for 30 seconds. No sense having a 100 HP running full on, and pumping nothing but air for hours at a time. Float repairs are another day.
 
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