Design Improvement of Stuffing Box Seals of Centrifugal Pump Shafts, Based on the Study of the Sealing Mechanism Physical Model

Author

Serhii S. Shevchenko, United Productions Atom LLC (36, Prokofiev St., Sumy, 40016, Ukraine), e-mail: s.shevchenko@united.productions, ORCID: 0000-0002-5425-9259

Abstract

Stuffing box seals are the most common type of pump rotor seals because they are adjustable and periodically restorable assemblies during operation.  Based on the study of physical processes, a sealing mechanism model of the stuffing box seal is formed as a combination of two successive hydraulic resistances: a pre-switch resistance, which is similar to a slotted choke, and a contact seal, where the shaft is directly sealed. The area where the packing contacts the shaft is the sum of the microregions where contact pressures occur. The system of labyrinth channels through which leakage occurs is physically closest to the filtration of fluid through a porous body layer. A method is proposed for calculating the stress state of the packing by solving the hydroelasticity problem. Obtained are expressions for calculating the gap and sealed pressure distribution over the radial stuffing box seal as well as leakage through the seal.  Radial and angular displacements of the shaft axis with respect to the axis of the stuffing box are taken into account, leading to the occurrence of additional contact packing pressures on the shaft and areas of weak contact of the packing with the shaft, which leads to increase in leakages. The desire to limit them encourages maintenance personnel to increase the axial compression of the packing, which leads to an even greater increase in local contact pressure. Proposed are stuffing box designs with a radially movable, self-aligning packing set relative to the shaft, which provide the equalization of contact pressure and increase in service life. Obtained are expressions for finding the minimum values of the parallel and angular misalignments, at which a stuffing box under the action of the centering force and moment starts tracking the shaft radial and angular displacements. Radial mobility prevents the areas of separation of the packing from the shaft and the formation of contact spots with increased pressure.

Keywords: stuffing box seal, sealing mechanism, contact pressure, misalignment, self-aligning.

Full text: Download in PDF

References

1. Gaft, J. & Marcinkowski, M. (2004). A choice of the seal for the shaft of the pump. Proceeding of the Pump Users International Forum, 29–30 sept. 2004, Karlsruhe, pp. 37–44.
2. Martsinkovsky, V. A. & Shevchenko, S. S. (2018). Nasosy atomnykh elektrostantsiy: raschet, konstruirovaniye, ekspluatatsiya [Pumps of nuclear power plants: Calculation, design, operation]. Sumy: University Book Publishing House, 472 p. (in Russian).
3. Marzinkovski, W., Gaft, J., & Sсhewtschenko, S. (2001). Calculation of flow and power losses to friction in radial stuffing box seal. Seals and Sealing Technology in Machines and Devices: Proceedings of IX International Conference, Wroclaw – Polanica Zdroj, pp. 108–115.
4. Gaft, J. Z. & Marzinkovski, W. A. (1997). Die untersuchung newer konstruktionen von radialen und axialen packungsdichtungen. X Internationales Dichtungs Kolloqium Unter-suchung und Anvendung von Dichtelementen, Steinfurt, Germany: Vortrage, pp. 182–205.
5. Diany, M. & Bouzid, A.-H. (2009). Analytical evaluation of stresses and displacements of stuffing-box packing based on a flexibility analysis. Tribology International, vol. 42, iss. 6, pp. 980–986. https://doi.org/10.1016/j.triboint.2009.02.002.
6. Diany, M. & Bouzid, A.-H. (2010). An experimental-numerical procedure for stuffing-box packing characterization. American Society Mechanical Engineers (ASME). Pressure Vessel and Piping Division, vol. 2, pp. 183–189. https://doi.org/10.1115/PVP2010-25012.
7. Derenne, M. & Masi, V. (2005). Predicting gasket leak rates using a laminar-molecular flow model. Proceedings of the ASME/JSME, PV. P. Conference, Denver, vol. 2, pp. 87–96.
8. Gaft, Ya. Z., Martsinkovskiy, V. A., & Zagorulko, A. V. (2002). Mekhanizm germetizatsii i raschet radialnykh salnikov [The sealing mechanism and calculation of radial oil seals.]. Tightness, vibration reliability and environmental safety of compressor equipment: Proceedings of 10 International Scientific and Technical Conference, Sumy, vol. 2, pp. 46–57 (in Russian).
9. Martsinkowsky, V., Gaft, J., & Gawlinsky, M. (1998). Contemporary tendencies of the gland packings improvement. Seals and Sealing Technology in Machines and Devices: Proceedings of VIII International Conference, Wroclaw – Polanica Zdroy, pp. 15–165.
10. Kazeminia, M. & Bouzid, A. (2004). Analytical and numerical evaluation of the sealing contact stress of different soft-packed stuffing-box. ASME-Turbo Expo Conference, Vol. 3B. Wind Energy-2004. Düsseldorf, Germany, pp. 16–20.
11. Marzinkovski, W., Gaft, J., & Sсhewtschenko, S. (2001). Konstruktionen und berechnung der dichtungen mit schwimmringen. Untersuchung und Anwendung von Dichtelementen: XII Internationales Dichtungskolloquium. 09–10.05.2001, Essen, Vulkan-Verlag, pp. 147–155.

Received 16 March 2020

Published 30 June 2020