Double mechanical seal
Among its many applications, the double seal is designed for pumping loaded water.
Below is an extract from the website of the manufacturer Savino Barbera:
"For special applications, Savino Barbera horizontal pumps (as an alternative to the single mechanical seal normally installed in the horizontal version of the corrosion-resistant centrifugal pumps) may also be equipped with open or closed circuit double mechanical seals flushed with suitable auxiliary liquids. This structural solution can resolve certain problems inherent to "normal" mechanical seals deriving from vaporization, the hazard of sticking seal faces, crystallization phenomena that affect some particular fluids pumped. For this reason, horizontal pumps equipped with this special double mechanical seal are especially appropriate for work where the risk of "running dry" is especially high, as in the case of discharging liquids from tank trucks: the seal's cooling circuit allows the pump to continue working without any difficulty, even if the liquid does not reach the pump itself."
You can find the full text here.
Thank you very much for your answer
Can you also tell me whether we can use them for:
2-without the appropriate auxiliary liquids?
Yes, the double mechanical seal is also used for vertical pumps.
The easiest way to determine what will work for you is to specify your needs and then ask a supplier to show you a suitable product offering.
On a single mechanical seal, the faces are lubricated against friction by the pumped fluid. If this liquid is clear, no worries. If it is loaded, though, better to use a double mechanical seal with a chosen barrier fluid (water for example) that will replace the pumped fluid between the seal faces. On several occasions, I have had the opportunity to switch from single seal pumps to double, and I can tell you the lifespan doesn't begin to compare, even with dry sludge in a progressive cavity pump. I also did this type of mounting on vertical pumps for the greater Paris Sanitation Authority more than 6 years ago and they've had 0 problems . A tank connected to the water network maintains sealing pressure, and the system operates in a closed circuit, so no water consumption. This is all the more attractive on a vertical pump because there is no risk of it running dry if an air pocket were to form under the seal (vertical position); the faces are permanently lubricated.