A back-to-back seal describes two shaft seals mounted back-to-back to provide a higher level of safety and reliability.
The term is commonly used in sealing engineering to describe an arrangement with two shaft seals mounted back-to-back.
The seal arrangement is suitable for toxic, explosive and poisonous liquids when no leakage from the pumped medium to the atmosphere can be accepted.
Between the two seals is a pressurised barrier fluid. The pressure of the barrier fluid is higher than the pump pressure. This means that any leakage will pass from the barrier fluid to the pumped liquid. The barrier fluid pressure must be minimum 2 bar or 10 % above the pump pressure. As the clean barrier fluid has a higher pressure, it also serves as a lubricant for all seal faces.
The back-to-back shaft seal arrangement is particularly suitable for viscous and/or abrasive media. The seal arrangement prevents the pumped medium from entering the seal gap and consequently prevents excessive wear.