Flow Switch to detect Seal Water

[BearB]

I need to install a flow switch to detect Seal Water to interlock the starting of a 2300v motor. Does anyone know of a product that they may have used in a simliar application?

 

[burnt2x]

We could help if enough data is presented. Is this a seal pot, vacuum break eqpt or what?

 

[BearB]

The seal is a mechanical seal, the rebuild kit is a graphite rope, that requires water to keep it from leaking. It is on a Hydra Pulper. That is all the information I have about the seal at this time.

 

[rovineye]

Any idea of what the flow rate and pressure is?

 

[roydm]

BearB,
I have had many bad experiences with flow switches, in particular where they spend a long time in the activated position. When you need them to work, they are stuck closed. In a clean lube oil application I have seen 50% failure. For this reason I almost never buy flow switches and I will not recommend one.
If you have a situation where the flow shuts off when the motor stops at least make sure that the switch indicates low flow as a permissive to re-start. Some mechanical seals have a very low flow rate, you might also consider using a pressure switch (water pressure at seal).
If it's a critical application I would recommend using a flow or pressure transmitter or at least a flow switch operating on the principle of rotating paddle e.g. Signet.
Good luck
Roy (Instrumentation consultant)

 

[BearB]

Thanks for the feedback, this site is always helpful in many ways.
The application is a HydraPulper(grinds paper with water into pulp)does this with a 2300v motor connected to an agitator in the bottom of the vessel. There is a Seal at the propeller that needs constant water flow for positive pressure that prevents the pulp from entering. The flow is less than 5 GPM. The seal that is being used is a John Crane Split Mechanical 37FS. The issue we have is water is left off, valve handle gets closed on a repair and days later when the seal goes bad it is notice. This is very costly to replace. I think the best prevention would be an inspection sheet but I need to get cost and layout together before I present both.

 

[ScottyUK]

Fit a position switch on the valve handle configured as either a start interlock or as a trip? We did this a few years ago on a 3750HP BFW pump, except it was a thrust bearing balance line which they kept leaving shut and which resulted in wiping out the thrust bearing. Now if the valve is shut then the pump won't run.


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If we learn from our mistakes I'm getting a great education!

 

[rovineye]

If your only concern is that valve position, you could put on a limit switch that closes when the valve is open. I have done that many times, but mostly for indication not as interlock.

I have had bad luck with flow switches as Roy said, esp at those low rates. When I need a flow switch I always try to have a pressure switch as well.

I will look up my flow switch models when back in office Monday.

 

[rovineye]

My favorite flow switches are made by ifm. Link below. I use SI-1000 series. They can learn what the normal flow rate is and can feed you a signal for hi (down stream leak) or low (upstream leak or valve closed) flow. Never had a reliability issue with these flow switches, but I do throw in a pressure switch as well.

 

[BearB]

Thanks all.