Design of the Springs Tightening for a Double Cartridge Mechanical Seal

Mechanical seals are used in a wide range of industrial applications, including pumps, compressors etc., in order to avoid leakage of the working fluid. The design construction, and the operation of the mechanical seals continue to evolve to meet the demands of new technologies and industries. These developments are the increase of operating parameters, in the condition of strictly respecting the environment protection. A mechanical seal consists of two rings, one being static and the other one dynamic, which are actioned by one or two fluid pressure, and an elastic force (or magnetic) which keeps the two faces of the rings in permanent contact. A direct contact between the frontal face of the rings will increase the surface temperature and the rings wear, so a small fluid film, as a lubricant and coolant, it is kept between the two face sealings. At modern mechanical seal are used also a secondary fluid. The tightening force in the seal, which it is very important, depends on seal construction, materials used, working fluid type, pressure and temperature, rotational speed, secondary fluid type, pressure, and temperature. Paper aims to present the studies made by the authors on a mechanical seal of the AESSEAL, cartridge seal type CDSA of a 1” in order to obtain the correct sealing pressure between seal rings. Calculation was made analytical, with the respect of regulations of the standards, and by FEA method. Was obtained a CFD model, to simulate the pressure inside the chamber of secondary fluid at different inlet/outlet pressures to determine the real value of it. The obtained results by CFD analyses were integrated in FEM analyses by ANSYS Static Structural to calculate the contact pressure on the rings faces and to calculate the minimum spring force for internal and external sealing cartridges for different working and secondary fluid pressure, also considering the seal construction design, materials, and rotational speed of 3000rpm. The results are very important in operation of the mechanical seal because the graphs presented in the paper give the operators the correct value of the spring tightening in the seal depending on the different ranges of fluids pressures.