What seal plan do submersible pumps use?

[AgsMyDude]

Most of the submersibles I've seen for industrial wastewater service use dual mechanical seals but it's not clear to me how they cool the seals or keep them clean. Wouldn't buildup occur in the primary seal as the process fluid evaporates across it? How is the secondary seal cooled?

 

[bimr]

Submersible pumps

 

[Snickster]

I would think that the objective would be 1) to keep debris in the liquid outside the pump from entering the space within the seals 2) to provided cooling to the seals. Select a seal plan to accomplish this. This would require fresh water flow into the seal chambers to push flow outward at a sufficient flow and pressure, so you can't use the pumped liquid - you need a separate fresh water source.

 

[TenPenny]

I think every submersible I've seen uses two seals with oil in between the seals.

The purpose of the seals is to prevent water from getting into the motor windings, and many of these pumps are fitted with a moisture detector to detect moisture in the oil so it can be pulled out and serviced before moisture ends up in the motor.

 

[AgsMyDude]

Thanks for the response all. The submersibles I've seen do not require seal external seal flush. I guess a better question would have been: If submersible can operate satisfactorily in dirty service without flush water, why do other pumps require seal flushes or cooling, even for dual seal plans? What is unique about submersibles?

 

[EdStainless]

What size of motors (10hp or 1000hp)?
What depth (10m or 5000m)?
What max temp (75C or 250C)?
Is the motor pressure equalized or just sealed?
Is the motor oil filled?
If it is oil filled then there will always be a very small amount of oil being forced out through the seal.

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P.E. Metallurgy, consulting work welcomed

 

[AgsMyDude]

The question is purely hypothetical. Most submersibles I've installed were for ambient or slightly elevated sumps for industrial waste or water runoff. I believe the motors were all oil-filled. I never understood how they get by without any kind of seal flush when horizontal pumps of similar sizes require it, even for dual seal plans like 53A/B

 

[TenPenny]

The main purpose of a seal plan is to remove the heat generated by the seal faces contacting each other.

Most submersible pumps are, well, submersed in water...so they are kept cool by the water.
There are a few 'dry running' submersibles that have a built in water jacket that circulates water around the motor and seal chamber to keep it cool.