DE2949868A1 - Sliding ring seal for pressurised water reactor coolant pump - has rings tilting to close gap as temperature rises - Google Patents

Abstract

A sliding ring seal consists of a stationary ring and revolving ring with radial sealing gap between them. To compensate the effects from temperature changes, one or both rings have incorporated deformation elements in the face adjacent to the sealing gap and/or in the face remote from it; these deformation elements have a coefficient of thermal expansion which acts in the opposite sense to that of the material of the two sliding rings so that, as the temperature rises, the deformation element or elements cause one or both rings to tilt towards the other. Used in particular as a hydrostatic seal for the main circulating pump of a pressurised water reactor. Also for other hydrostatic sliding ring seals.

Description

Mechanical seal

The invention relates to a mechanical seal consisting of a stationary and a rotating sliding ring, between which a radially directed Sealing gap is arranged, additionally attached, other coefficients of thermal expansion having rings compensate for temperature influences acting on the sliding rings.

The known mechanical seal designs have the property on that the seal leakage increases with increasing fluid temperature. Conditional is this behavior due to a deformation that occurs when the temperature rises the sliding rings, which causes a change in the sealing gap. Acquaintance Remedial measures such as those shown in U.S. Patent 3,015,504 see a specific one Design and mounting of the sliding ring before a change in the sealing gap counteract this and constantly maintain an even and parallel sealing gap. The cause of such changes are the materials used and their different thermal expansion coefficients and coefficients of thermal conductivity.

Also with the object according to DE-PS 19 07 723 was tried with Wrestling with different coefficients of thermal expansion a uniformity of the To ensure sealing gap.

Another problem with such seals arises from the temperature-dependent viscosity of the fluid used in each case.

In general, the system is important for continuous operation of the seal limits the maximum amount of leakage at full system pressure.

The minimum amount of leakage, however, is because of the minimum gap width given by the seal. As a result of the different caused by the temperature Viscosity of the fluid, it is not possible to have a large cold leak during start-up to realize and at the same time not the maximum amount of leakage in normal operation To exceed.

Further difficulties arise when measuring the respective Leakage amount. As a rule, standardized quantity measuring devices are used for this purpose Measuring range is 1: 10, so that cases can arise in which as a result larger The measuring range of the measuring device is no longer sufficient as leakage quantities increase. Special in the case of hydrostatic seals, due to the increasing flow velocities change the flow condition in the Dk $ .lspalt and lead to a sudden change in the Lead leakage behavior.

The invention is based on the object by means of a little complex Device to influence the amount of leakage from a mechanical seal ur) d within of the measuring range of a standardized quantity measuring device.

The solution to this problem provides that in the one facing the sealing gap Area and / or in the area facing away from the sealing gap of one or both seal rings a deformation element is inserted, which in a known manner a for Thermal expansion coefficients of the sliding ring opposing thermal expansion coefficients and that the deformation element has a sliding ring when the temperature rises or both slip rings are tilted towards each other. This makes it possible to start up to allow a larger amount of cold leakage and this amount with increasing temperature as well as the changing viscosity of the mechanical seal. Damage or excessive signs of wear during start-up can thus be largely prevented. The one determined by the choice of material thermal tilting of the sliding rings and thus their sealing surfaces enables the Operation of a mechanical seal in which the viscosity of the fluid used has no Influence can exert more on the leakage behavior. Added to this is the advantage of more uniform and, viewed as a whole, less leakage and thus their easier metrological acquisition.

The embodiment of the invention provides that the deformation element in rod form arisgebi lciet is rind several deformation elements in the radial direction are arranged within the slip ring. By means of this measure and dependent the coefficient of thermal expansion of the sliding ring material can be selected Set by the rods with small or thermal expansion coefficient the thermal Influenced growth of the slip rings and a reliable control of the amount of leakage achieved will.

According to another embodiment of the invention, the deformation element is ring-shaped in a manner known per se. The attachment of the thermal Tilting of the sealing surfaces controlling elements can be made by the various known Processes are carried out, such as build-up welding, brazing, shrink connections, Cold pressing process and the like.

An embodiment of the invention is shown in the drawings and is described in more detail below. For the example a hydrostatic Seal of a main coolant pump of a pressurized water reactor selected the subject the invention is also readily applicable to hydrostatic mechanical seals or combinations thereof are applicable. It show the Fig. 1 the pressure and temperature dependent leakage curves of the known previous designs, FIG. 2 shows the heating curve for the amount of leakage of the previous embodiment, FIG. 3 + 4 the curve shape of FIGS. 1 and 2 and the modified by the invention Fig. 5 shows a practical embodiment of the invention.

In the diagram of FIG. 1, the amount of leakage is on the abscissa axis Q plotted in percent and on the ordinate axis that in the application selected here corresponding pressure p in bar. The operating pressure here is 150 bar. The curve 1 shows the amount of leakage, which increases with increasing pressure, at a temperature of 20 ° C. With increasing temperature this curve shifts to the right and e.g. at an operating temperature of 75 ° C, the amount of leakage is shown in the curve 2 a.

In the diagram of FIG. 2, the amount of leakage is on the abscissa axis Q in percent and the temperature t of the leak in OC on the ordinate axis. Line 3 of this heating diagram shows how the temperature rises the The amount of leakage increases. If you want the Increase cold leakage, so in normal operation there is a larger and undesirable one Heat leakage a.

When the invention is used, those shown in FIGS. 3 and 4 result Curves. The structure of the diagrams corresponds to that of the corresponding diagrams of FIGS. 1 and 2.

Fig. 3 shows with the curve 4 that in start-up operation, so at low Pressures and low temperatures, there is a much larger amount of leakage is what happens with increasing temperature and due to each other Tilting of the slip rings is reduced. Curve 5 shows the lower amount of leakage at an operating temperature of e.g. B. 75 OC and a selected operating pressure of 1 50 bar. The comparison of FIG. 3 with FIG. 1 shows how with the inventive Design at a start-up pressure of e.g. 15 bar that shown by curve 4 Cold characteristic with approx. 30% of the design leakage in a substantially safe operating range lies than the approx. 10% of the cold characteristic curve shown in curve 1 of the conventional one Mechanical seal.

The now smaller hot leakage at a start-up pressure of z. B.

15 bar is irrelevant, as warm operation with full operating pressure is linked to the system or can be linked easily.

From Fig. 4 it can be seen that a seal is used here, in which the amount and type of material controlling the tilting of the sliding rings is chosen became that the viscosity-dependent change in leakage was overcompensated. As the Line 6 shows, there is a reduction in the amount of leakage as the temperature increases. The thermal deformation, controlled to a certain extent by the choice of material, is made possible thus independent of the viscosity-dependent coupling of cold and warm characteristics any arrangement of the respective heating curve.

Fig. 5 shows an embodiment of the invention in section.

When the sliding ring 7 is stationary, the deformation element 8 is in the surface 10 facing the sealing gap 9 is arranged. The one with the one standing still Sliding ring 7 cooperating rotating sliding ring 11 has in this embodiment also has a deformation element 8, but here on the one facing away from the sealing gap 9 Surface 1 2 of the slip ring 11 is attached. Depending on the circumstances, it can also an arrangement of the deformation elements other than the one shown takes place. in the When the mechanical seal is in the idle or initial state, there is a parallel sealing gap 9. With increasing warming of the mechanical seal and the liquid to be sealed takes place - as shown - a warping of the slip rings, one on top of the other to be carried out Tilting of the surfaces forming the sealing gap 9 means. Thus, the amount of leakage from the mechanical seal can be measured with simple means be managed. As the temperature decreases, there is consequently a parallel one Alignment of the surfaces delimiting the sealing gap.

Claims (3)

Claims mechanical seal, consisting of a fixed and a rotating seal ring, between which a radially directed sealing gap is arranged, with additional thermal expansion coefficients attached to the slip rings having rings compensate for temperature influences acting on the sliding rings, characterized in that in the surface facing the sealing gap (9) and / or in the surface of one or both sliding rings (7, 11) facing away from the sealing gap (9) a deformation element (8) is inserted, which in a known manner a behave in the opposite way to the coefficient of thermal expansion of the sliding ring Has thermal expansion coefficient and that the deformation element with increasing temperature (8) one sliding ring or both sliding rings (7.1!) Tilted towards each other. 2. Mechanical seal according to claim 1, characterized in that the deformation element (8) is in the form of a rod and a plurality of deformation elements are arranged in the radial direction within the sliding ring (7, 11). 3. Mechanical seal according to claims 1 and 2, characterized in that that the deformation element (8) is annular in a known manner is.