Hecker® AEGIRA® HN 490 Cartridge seal with gaslubricated mechanical seals for special applications

HN 490 Hecker AEGIRA^®-Cartridge seals with gas-lubricated mechanical seals are suitable in applications, where conventional mechanical seals can only operate with large problems or a high technical effort and if a small drag-in of buffer gas into the process liquid can be tolerated. A typical application can be the shaft sealing of mixers and agitators in the pharmaceutical industry where the contact of liquid from a conventinal locking circuit with the process fluid has to be strictly avoided.

Gas-lubricated seals show several advantages in comparison to conventinal liquid lubricated mechanical seal

·         Encreased security

With conventional locking systems always exists the risk of a spontanous failure of the seal at the product side with the result that the whole contents of the locking fluid system penetrates the reactor, contaminating the process fluid and causing high costs. Gas lubricated seals can avoid such severe accidents sure.

·         Significant smaller friction losses

Example:  A locking system for conventional fluid-lubricated mechanical seal with shaft size 50 mm, shaft speed 3000 min^–1 and an operating pressure of 8 bar generates powerlosses by friction of the sliding faces of about 700 W, additional the powerlosses by churning the surrounding liquid of about 100 W. These powerlosses must be brought up from the driving engine. Since the powerlosses will be absorbed by the locking fluid, that leads to heating up, great additional efforts  are necessary to cool down the locking fluid. In comparison to this the powerlosses by friction in the gap between the sliding faces of two gas seals as the part of a buffer system are to be  about 4 W. The essential reduction of the power losses leads to a reduction of the operating expenses.

·         Low efforts for buffer system

Conventional locking systems  consist of a very expensive arrangement of pressure supply system, pressure tanks, cooling system, circulation pump, level control etc. Gas-lubricated mechanical seals need in addition to a connection to the compressed-gas plant, which is installed in the plant and supplies with buffer gas, for example compressed air or nitrogen, only a simple and cheap gas supply system according to picture 2.

·         Low wear and long life time

Except of the region of low shaft speed while starting up and shut down the sliding faces are seperated completely by a gas film. Therefore the sliding faces operate practically without wear. In the case of fluid-lubricated mechanical seals without special grooves for hydrodynamic pressure generation, the natural pressure generation is not sufficient to ensure the seperation of the sliding faces. Wear occurs inevitable. The life time is limited. Wear and high friction can only be avoided by the means of expensive measures for hydrodynamic pressure generation, which consequently lead to a high leakage rate. Therefore gas lubricated mechanical seals are a cost-effective alternative.

Gas lubricated mechanical seals from Hecker can be delivered with different designs. Picture 1 shows in the  above sectional view a design with rotating sealfaces in back-to-back. The below sectional view shows a design with a stationary seal face on the product side. Both designs can be delivered in different sizes. The connecting dimensions can be adapted individual. Standard of materials is silicon carbide (Q1) in combination with antimony impregnated carbon (A). They seals of the type HN 490 can be used for operating pressures up to 20 bar and sliding velocities up to 20 m/s. Dependant on the material of the o-rings the temperature-range includes –40°C up to 200°C.

Picture 3: Standard values for gas-leackage for different shaft diameter d with shaft speed 3000 min -1. consumption of buffer gas is the addition of the leackage values of both seals.