Double Mechanical Seal Cooling Water Leakage

• How old is the seal assembly? In what condition is it?
• What is the level of filtration of each of the two water streams?
• Is 50degC water a permanent solution? If not, why not?
• What is the pressure of each of the two streams and how do these pressures compare with the seal's pressure rating?
• How does the actual flowrate compare with specification, and with design?
• What has the seal manufacturer's local technical representative had to say about the installation in his/her visit inspection report?
• Etc.

Cooling Water side is city water

Process Side is pigments, oil/water emulsion

50°C is not preferred per the manufacturer due to seal life issues. Also I have had other installations running for years that have never had this issue. This is a 2 month old unit)

All pressures are well within tolerances

Manufacturer believes that the seal has product on it that is causing the seal faces to open, not sure why it stops with hot water and starts with cold. They will be in shortly to inspect.

This is a small unit (<1/2" shaft) runs at high speed up to 20 meters/sec

Thank you

<...They will be in shortly to inspect....>

Wait, then.

Could it be that dried pigment gets between the faces of the seal and the cold water won't dissolve it but the hot water does thereby removing the particles that are holding the seal faces apart? You do say that it is a pigment-oil-water solution so I would assume the water would dissolve the particle and perhaps the hotter water does a better job at it. Hard to believe that 122 degree F (50 degree C)water would injure a seal. What are the seal face materials? Carbon against TC?

Strange thing is that it stops with the hot water but as soon as you switch back to cool water it starts again... Yes carbon and TC.

What is the pressure of the hot water supply?

Both are the same city water hot and cold

What temperature is maintained in the vessel? Is it possible that the pigment is just more soluble in the hot water or that the cold water causes precipitation out of solution? If you are always maintaining a higher pressure inside the stuffing box area (between the two seals) then I wonder how the pigment can get between the seal faces which I would assume only happens on the vessel side seal face and that you are getting excessive leakage into the vessel. Is this a batch process where the vacuum is removed at times to unload the vessel? Do you clean out the vessel between batches and is it possible that the seal water gets turned off and the vessel gets pressurized so as to open the seal if the inlet valve isn't shut off? Hard to solve a puzzle with too few clues or pieces.

You stated "Both are the same city water hot and cold", but have you actually checked the pressure with a gauge?

You could have an unknown problem on the cold water that is reducing the pressure and or flow. Check it out before the seal rep arrives, if they know their stuff that should be one of the first things they ask.

Perhaps the cooler water is causing metal parts to shrink at a faster rate and opening the seal? It may be that the new part is a looser fitting than others in an attempt to reduce seal wear but has become a problem with the cooler water creating a larger gap than the hot water does in the same vessel.

The springs would prevent that from happening. See below as a typical double cartridge seal arrangement. No manufacturer would produce a product that would that to happen. The Requirements of API Standard 682 require safety at all conditions and such a premise would disqualify the seal not to mention setting the manufacturer up for product liability lawsuits.

Figure 3. Double external mechanical seal

"The use of double-mechanical seals with flushing solution and suitable flow-activated pump protection have been known to operate for years on critical applications that would otherwise damage single-seal pumps within weeks, days, or even only a few minutes. The elimination of troublesome downtime, service work, solution loss, or possible loss of a hazardous material are all reasons for using a double seal. Should there be occasions when a source of water is not available, then a self-contained system that includes a pump, a reservoir of liquid, and a filter could be employed to recirculate the water as needed (Figure 4). The size of the chamber containing the liquid would need to be large enough to handle the heat input from the product being pumped or the energy created at the seal faces themselves."

Note the springs forcing both sets of the seal faces together.