RU2600209C1 - End seal - Google Patents

Abstract

FIELD: pumps.

SUBSTANCE: invention relates to end seals of rotors of pump units for separation of media or pressure difference. Invention can be used in pumps used at nuclear power stations, in particular, main circulation pumps. Multistage design of face seal comprises series-arranged working stages and end stage each of which includes located on a shaft a rotary element and in contact with it a spring-loaded axially movable stator element, sealed relative to housing by sealing rings wherein cavities of high and low pressure of working stages are connected in series with throttle holes in stator element, that is designed to execute function of axially moving sealed relative to housing of stepped piston. Here is disclosed a formula dependency of outer diameters of stages of piston of stator element. Said ratio provides absence of additional force on stator element during its normal operation, enabling, in case of seal opening, enhancing effect on stator element for closing seal, due to hydrostatic forces acting on piston.

EFFECT: higher reliability and manufacturability of parts and assembling of seal.

1 cl, 1 dwg

Description

The invention relates to mechanical seals of rotors of pumping units for separating media or differential pressure.

The invention can be used in the design of pumps used in nuclear power plants, in particular main circulation pumps.

A known block of mechanical seals (RF Patent No. 2084730, publ. 20.07.1997, IPC F16J 15/34). This design is a multi-stage mechanical seal containing sequentially installed working stages and an end stage, each of which includes a rotor element located on the shaft and a spring-loaded axially movable stator element in contact with it, sealed with a sealing ring relative to the housing, and high and low pressure cavities of the workers steps are connected in series by throttle holes in the stator housing. A stepped cylindrical bore is made in the housing parallel to the shaft axis, communicating in a smaller diameter with a high-pressure cavity, and in larger - with a low-pressure cavity, in which axially movable stepped cylindrical pistons are installed, sealed in bores of a larger and smaller diameter with the possibility of interaction of the piston end smaller diameter with a stator element. This design serves to force each seal stage to be closed, if opened, by supplying the unit with power step pistons in addition to the springs. The design drawback is the presence of an additional mechanical assembly - a piston, which can affect the product’s performance if it is jammed, for example, in the lowest position. This can lead to the destruction of the friction pair of the seal. Also in the design of the mechanical seal there is a structural flaw associated with the operation of the piston. Due to the fact that the piston is stepped, during its operation between the end surface, limited by the diameters of the larger and smaller cylinders, as well as the counter end surface in the housing, a cavity with a variable volume is formed. Due to the complete tightness of the cavity, a rarefaction or compression of the medium enclosed in the volume of the cavity will be created in it. This effect will prevent the free movement of the piston and, as a consequence, its correct operation.

The tasks solved by the invention:

- improving the reliability of the mechanical seal by reducing the number of movable nodes;

- improving manufacturability by simplifying assembly and reducing the number of parts in the product.

In the implementation of the invention can be obtained, in particular, the following technical results:

- reducing the time for maintenance of the mechanical seal;

- reduction of metal by reducing the number of parts.

As a solution to the problem, which allows to achieve a technical result, a mechanical seal design is proposed that differs from the prototype in the following.

A multistage mechanical seal comprising successively mounted working stages and an end stage, each of which includes a rotor element located on the shaft and a spring-loaded axially movable stator element in contact with it, sealed with sealing rings relative to the housing, and the high and low pressure cavities of the working stages are connected in series throttle holes made in the stator element. The housing, in turn, consists of an external cylinder, in which a stepped and a thrust ring are installed sequentially, one per step. The thrust ring serves to abut the spring between it and the stator element. The stator element and the stepped ring of the housing are made so that the stator element acts as an axially movable step piston sealed with rubber seals, while a part of the piston with a smaller diameter is located in the high-pressure region - before the seal, and the second part with a large outer diameter is on the smaller side pressure or behind the seal. In the region of transition of the smaller cylinder to the larger cylinder, a low is made on the stator element. In turn, in the stepped ring corresponding to the stator element, a through hole is made in the area of transitions of the cylinder diameters of the reciprocating piston of the stator element so that, at any position of the stator element, it does not go beyond the borders of the casing on it. This hole serves to compensate for rarefaction-compression in the volume of the cavity formed during movements of the stator element. The seal of the hole in the housing is realized between the outer cylinder and the stepped ring by two rubber rings between which it is located.

, где D₁ - меньший диаметр поршня статорного элемента, D₀ - внутренний диаметр статорного элемента, P₁ - давление перед уплотнением, со стороны за уплотнением на поршень статорного элемента действует сила $$F_2=P_2\times \pi \frac{D_2^2-D_0^2}{4}$$

, где D₂ - больший диаметр поршня статорного элемента, Р₂ - давление за уплотнением, равное kP₁, где k(0<k<1) - коэффициент снижения давления за счет дросселя в статорном элементе. Для того чтобы в рабочем положении на статорный элемент действовала только сила пружины, необходимо чтобы силы F₁ и F₂ были равными, для этого $$D_2=\sqrt{\frac{D_1^2-D_0^2\left(1-k\right)}{k}}$$

. В случа, когда уплотнение раскрывается, давление за уплотнение, Р₂ выравнивается по значению с давлением перед уплотнением Р₁, в результате чего на поверхность поршня статорного элемента за уплотнением начинает действовать сила $$F_2^{\text{'}}=F_1\times \frac{D_2^2-D_0^2}{D_1^2-D_0^2}$$

, больше, чем перед уплотнением, что заставляет его перемещаться в сторону закрытия разъема. Для компенсации изменений объема в камере поршня при его перемещениях область, образованная обнизкой на статорном элементе, ответной частью ступенчатого кольца и сквозным отверстием соединена с расширительной емкостью.The operation of the seal is as follows. During normal operation of the block of mechanical seals using throttle holes at each working stage of the seal, a part of the working pressure is triggered, depending on the capacity of the throttle. As a result, a force acts on the piston of the stator element from the side before the seal $$F_{\mathrm{one}}=P_{\mathrm{one}}\times \pi \frac{D_{\mathrm{one}}^2-D_0^2}{\mathrm{four}}$$

where D ₁ is the smaller diameter of the piston of the stator element, D ₀ is the inner diameter of the stator element, P ₁ is the pressure before the seal, from the side behind the seal, the force acts on the piston of the stator element $$F_2=P_2\times \pi \frac{D_2^2-D_0^2}{\mathrm{four}}$$

where D ₂ is the larger piston diameter of the stator element, P ₂ is the pressure behind the seal, equal to kP ₁ , where k (0 <k <1) is the coefficient of pressure reduction due to the throttle in the stator element. So that in the working position on the stator element acted only by the force of the spring, it is necessary that the forces F ₁ and F ₂ were equal, for this $$D_2=\sqrt{\frac{D_{\mathrm{one}}^2-D_0^2\left(\mathrm{one}-k\right)}{k}}$$

. In the case when the seal opens, the pressure behind the seal, P ₂ equalizes in value with the pressure before the seal P ₁ , as a result of which the force begins to act on the piston surface of the stator element behind the seal $$F_2^{\text{'}\text{'}}=F_{\mathrm{one}}\times \frac{D_2^2-D_0^2}{D_{\mathrm{one}}^2-D_0^2}$$

, more than before the seal, which makes it move towards the closing of the connector. To compensate for volume changes in the piston chamber during its movements, the region formed by the low on the stator element, the counterpart of the stepped ring and the through hole is connected to the expansion tank.

The invention is illustrated in the drawing, which shows a General view (axial section) of the mechanical seal.

The multi-stage mechanical seal consists of a housing 10 made in the form of an external cylinder, in which step 11 and thrust 12 rings are mounted one at a time, as well as rotor elements 3 located on the shaft with contact surfaces 1 and spring-loaded axially movable stator elements in contact with them 4 with contact surfaces 2.

Between the thrust rings 12 and the movable stator elements 4 springs 13 are mounted, providing a compressive force between the contact surfaces 1 and 2.

The high pressure cavities 7 formed by the stepped rings 11, the stator elements 4 and the rotor elements 3 are connected to the low pressure cavities 8 formed between the thrust rings 12, the stepped rings 11, the stator elements 4 and the rotor elements 3, the throttle openings 9 made in the stator elements 4.

The cavities of high and low pressure are separated by rubber rings 6.

The stator element 4 and the stepped ring 11 are designed so that the stator element acts as an axially movable stepped piston, with a part of the piston with a smaller diameter located in the high-pressure region — before the seal, and the second part with a larger outer diameter — from the side of the lower pressure or behind seal. In the region of transition of the smaller cylinder to the larger one, the stator element 4 is lowered 14. In turn, in the stepped ring 11 corresponding to the stator element 4, a through hole 15 is made in the region of transitions of the diameters of the cylinders so that at any position of the stator element it does not go out of bounds downs on it. This hole serves to compensate for rarefaction-compression in the volume between the stepped ring 11 and the stator element 4 bounded by the rubber rings 6 of the resulting cavity when the stator element 4 is moved.

The seal of this volume between the outer cylinder 10 and the stepped ring 11 is made of two rubber rings 5.

, где D₁ - меньший диаметр поршня статорного элемента, D₀ - внутренний диаметр статорного элемента, Р₁ - давление со стороны полости высокого давления. Со стороны полости низкого давления 8 на поршень статорного элемента действует сила $$F_2=P_2\times \pi \frac{D_2^2-D_0^2}{4}$$

, где D₂ - больший диаметр поршня статорного элемента, Р₂ - давление со стороны полости низкого давления, равное kP₁, где k(0<k<1) - коэффициент снижения давления за счет дросселя в статорном элементе. Для того чтобы в рабочем положении на статорный элемент 4 действовала только сила пружины 13, необходимо чтобы силы F₁ и F₂ были равными, для этого $$D_2=\sqrt{\frac{D_1^2-D_0^2\left(1-k\right)}{k}}$$

. В случае когда уплотнение раскрывается, давление в полостях выравнивается, в результате чего на поверхность поршня статорного элемента начинает действовать сила $$F_2^{\text{'}}=F_1\times \frac{D_2^2-D_0^2}{D_1^2-D_0^2}$$

, что заставляет его перемещаться в сторону закрытия разъема.The operation of the seal is as follows. During normal operation of the block of mechanical seals using throttle holes 9 at each working stage of the seal, a part of the working pressure is activated, depending on the capacity of the throttle. As a result, a force acts on the piston of the stator element 4 from the side of the high-pressure cavity 7 $$F_{\mathrm{one}}=P_{\mathrm{one}}\times \pi \frac{D_{\mathrm{one}}^2-D_0^2}{\mathrm{four}}$$

where D ₁ is the smaller diameter of the piston of the stator element, D ₀ is the inner diameter of the stator element, P ₁ is the pressure from the side of the high-pressure cavity. From the side of the low-pressure cavity 8, a force acts on the piston of the stator element $$F_2=P_2\times \pi \frac{D_2^2-D_0^2}{\mathrm{four}}$$

where D ₂ is the larger diameter of the piston of the stator element, P ₂ is the pressure from the side of the low pressure cavity equal to kP ₁ , where k (0 <k <1) is the coefficient of pressure reduction due to the throttle in the stator element. In order that in the working position on the stator element 4 act only the force of the spring 13, it is necessary that the forces F ₁ and F ₂ were equal, for this $$D_2=\sqrt{\frac{D_{\mathrm{one}}^2-D_0^2\left(\mathrm{one}-k\right)}{k}}$$

. In the case when the seal opens, the pressure in the cavities is equalized, as a result of which a force begins to act on the surface of the piston of the stator element $$F_2^{\text{'}\text{'}}=F_{\mathrm{one}}\times \frac{D_2^2-D_0^2}{D_{\mathrm{one}}^2-D_0^2}$$

, which makes it move towards the closing of the connector.

To compensate for pressure changes in the volume formed between the stepped ring 11, the stator element 4 and limited by the rubber rings 6 formed during the movements of the stator element 4, it is connected to the expansion tank outside the mechanical seal through the hole 15.

Claims (2)

1. An end-face seal containing successively mounted working stages, each of which includes a rotor element located on the shaft and a spring-loaded axially movable stator element in contact with it, sealed with o-rings relative to the housing, the high and low pressure cavities of the working stages being connected in series with throttle openings, characterized in that
the housing consists of an external cylinder and sequentially mounted step and thrust rings, one per step, the step ring being sealed relative to the cylinder and responding to the stator element, and the thrust ring acts as a stop for the spring between it and the stator element,
throttle openings are made in the stator element, which, in turn, is designed to perform the functions of an axially movable step piston sealed relative to the step ring of the housing, while a part of the piston with a smaller diameter is located in the high pressure region — before the seal, and the other part with a large outer diameter - from the side of lower pressure or behind the seal,
also in the outer cylinder of the housing and the stepped ring, in the area of transitions of cylinder diameters corresponding to the piston of the stator element, a through hole is made connecting the formed cavity between the housing and the stator element with an expansion tank. 2. The mechanical seal according to claim 1, characterized in that the outer diameters of the piston stages of the stator element are made with the ratio

where D ₂ is the diameter of the larger piston cylinder; D ₁ - the diameter of the smaller cylinder of the piston; D ₀ is the inner diameter of the stator element; k is the coefficient of pressure reduction due to the throttle in the stator element.

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