Constant pressure packing seal

Abstract

The application discloses a constant-pressure packing seal, which comprises a housing base, a packing gland, packing, a packing box and a pressure regulating mechanism; the housing base is sleeved on the outer side of a main shaft and forms a shaft seal chamber with the main shaft; the packing gland is sleeved on the outer side of the main shaft and is connected to the top of the housing base; the packing is filled between the packing gland, the housing base and the main shaft; the packing box is arranged on the outer side of the housing base; and the pressure regulating mechanism is arranged on the housing base and cooperates with a flow channel in the housing base. The application can maintain the relative constancy of the packing seal inlet pressure and adapt to the operation conditions of the shaft seal chamber pressure variation.

Description

TECHNICAL FIELD

[0001] The present application relates to a shaft seal chamber of a rotary machine, and more particularly to a constant pressure packing seal. BACKGROUND

[0002] The packing seal structure is simple, reliable in operation, and low in maintenance cost in later period, and is the most widely used sealing form in rotary machines. The packing seal mainly relies on the contact surface between the packing and the rotating shaft to realize the sealing effect. In engineering design, the packing is filled into the space between the rotating shaft and the packing housing by the packing gland through the connecting bolts, so as to realize the sealing effect, and therefore the packing compression is crucial to the effectiveness of the entire packing seal.

[0003] The packing compression degree is based on the sealing cavity pressure. In actual engineering application, the packing gland is compressed in real time based on the sealing cavity pressure in the field operation, so as to control the packing leakage at about 6 drops per minute. If the packing is compressed too tightly, the leakage is reduced, but the friction between the packing and the shaft sleeve is increased, the mechanical efficiency is reduced, and in severe cases, the sintering between the rotating shaft and the packing is caused. If the packing is compressed too loosely, the leakage is increased, the volume loss of the entire unit is increased, and the sealing is failed.

[0004] In recent years, with the rapid development of frequency conversion technology, the frequency conversion technology is more and more widely used in rotary machines. When the rotary machine adopts the frequency conversion technology, the shaft seal chamber pressure changes due to the change of the rotating speed, and the working condition is not constant pressure, which seriously restricts the application of the packing seal. If the packing compression is based on the low rotating speed working condition, when the unit is operated at high rotating speed, the shaft seal chamber pressure is increased, and at this time, the packing compression degree is relatively loose, the leakage is inevitably increased, and then the overall efficiency of the unit is reduced due to the increase of the volume loss. If the packing compression is based on the high rotating speed working condition, when the unit is operated at low rotating speed, the shaft seal chamber pressure is reduced, and at this time, the packing compression degree is relatively tight, the leakage is greatly reduced, the heat generated by the friction between the packing and the shaft cannot be removed in time, and the sintering between the shaft and the packing is caused, and even more serious accidents are caused. SUMMARY

[0005] In view of the many difficulties encountered by the packing seal in the prior art in the variable frequency working condition, the purpose of the present application is to provide a constant pressure packing seal, which can maintain the relative constancy of the packing seal inlet pressure, so as to adapt to the variable pressure working condition of the shaft seal chamber.

[0006] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0007] A constant pressure packing seal, comprising a housing base, a packing gland, a packing, a packing housing and a pressure adjusting mechanism;

[0008] The housing base is sleeved on the outside of the main shaft, and forms a shaft seal chamber with the main shaft;

[0009] The packing gland is arranged on the outside of the main shaft and is connected to the top of the housing base;

[0010] The packing is filled between the packing gland, the housing base and the main shaft;

[0011] The packing chamber is arranged on the outside of the housing base;

[0012] The pressure regulating mechanism is arranged on the housing base and cooperates with the flow channel in the housing base.

[0013] Preferably, a plurality of tooth-shaped grooves are arranged on the inner side of the housing base to form a labyrinth seal with the main shaft.

[0014] Preferably, the flow channel in the housing base is in the shape of a circular hole; and

[0015] The housing base is further provided with a mounting hole which is perpendicular to the flow channel.

[0016] Preferably, the pressure regulating mechanism comprises a valve body, a spring, a valve cover, a locking nut, a stop block and an adjusting nut;

[0017] The valve body is arranged in the mounting hole and coaxially arranged with the mounting hole;

[0018] One end of the valve cover is arranged on the mounting hole to seal the mounting hole;

[0019] The stop block is arranged on the other end of the valve cover;

[0020] The spring is horizontally arranged in the valve cover and the mounting hole, one end of the spring is in contact with the valve body and the other end is in contact with the stop block;

[0021] The adjusting nut is screwed on the other end of the valve cover through the locking nut, and the adjusting nut cooperates with the stop block;

[0022] The valve body is provided with a circular hole which is in communication with the flow channel.

[0023] Preferably, the housing base and the packing gland are connected through an adjusting screw and a fixing nut.

[0024] Preferably, a water seal ring is further arranged between the packing, the housing base and the main shaft.

[0025] Preferably, the housing base, the packing gland, the packing and the packing chamber are all in a split structure.

[0026] The constant pressure packing seal provided by the present application has the following advantages:

[0027] 1) The constant pressure type packing seal has simple structure and low cost, and has good economy;

[0028] 2) The constant pressure type packing seal has split structure of the housing base, the packing gland, the packing and the packing housing, and is convenient to install and maintain;

[0029] 3) The constant pressure type packing seal has waste liquid recovery function, and is convenient to process the leaked liquid;

[0030] 4) The constant pressure type packing seal can maintain the pressure in the packing inlet cavity at a relatively constant state by dynamic balance between the shaft seal pressure and the adjusting spring force, and has wide speed range and stable and reliable operation. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 is a structural schematic view of the constant pressure type packing seal of the present application;

[0032] Figure 2 is an enlarged schematic view of part A in Figure 1

[0033] Figure 3 is a trajectory schematic view of the constant pressure type packing seal of the present application under low speed working condition;

[0034] Figure 4 is a trajectory schematic view of the constant pressure type packing seal of the present application under high speed working condition. DETAILED DESCRIPTION

[0035] In order to better understand the above technical solutions of the present application, the technical solutions of the present application are further described below in combination with the drawings and examples.

[0036] As shown in Figure 1 and Figure 2 , the constant pressure type packing seal provided by the present application can maintain the pressure at the packing seal inlet at a relatively constant state by the pressure adjusting device of the present application when the pressure in the shaft seal chamber changes, and further adapt to the variable frequency operation of the unit, and comprises a housing base 1, a packing gland 4, a packing 5, a packing housing 6 and a pressure adjusting mechanism.

[0037] The housing base 1 is sleeved on the outer surface of the main shaft 14, and forms a shaft seal chamber with the main shaft 14.

[0038] The packing gland 4 is also sleeved on the outer surface of the main shaft 14, and is connected and fixed on the top of the housing base 1 through the adjusting screw 2 and the fixing nut 3 to seal the shaft seal chamber.

[0039] The packing 5 is filled in the position between the packing gland 4, the housing base 1 and the main shaft 14.​

[0040] The stuffing box 6 is arranged on the outer side of the stuffing box base 1.

[0041] The water seal ring 6 is further arranged between the stuffing 5, the stuffing box base 1 and the main shaft 14.

[0042] The stuffing box base 1, the stuffing gland 4, the stuffing 5 and the stuffing box 6 are all of split type structure, so that the installation and subsequent maintenance of the constant pressure type stuffing seal are very convenient.

[0043] The pressure regulating mechanism is arranged on the stuffing box base 1 and cooperates with the flow channel in the stuffing box base 1.

[0044] The inner side of the stuffing box base 1 is provided with a plurality of tooth-shaped grooves, which form a labyrinth seal with the main shaft 14.

[0045] The flow channel 15 in the stuffing box base 1 is in the shape of a circular hole; and the stuffing box base 1 is further provided with an installation hole 16 which penetrates the flow channel 15 vertically.

[0046] The pressure regulating mechanism comprises a valve body 8, a spring 9, a valve cover 10, a locking nut 11, a stop block 12 and an adjusting nut 13.

[0047] The valve body 8 is arranged coaxially between the installation hole 16.

[0048] One end of the valve cover 10 is arranged on the installation hole 16 to seal the installation hole 16.

[0049] The stop block 12 is arranged on the other end of the valve cover 10, and the head of the stop block 12 penetrates the end of the valve cover 10 and is located outside the valve cover 10.

[0050] The spring 9 is horizontally arranged in the valve cover 10 and the installation hole 16, one end of the spring 9 is in contact with the head of the valve body 8, and the other end of the spring 9 is in contact with the tail of the stop block 12.

[0051] The adjusting nut 13 is screwed on the outer side of the other end of the valve cover 10 through the locking nut 11, and the inside of the adjusting nut 13 is in contact with the head of the stop block 12 to form cooperation.

[0052] The valve body 8 is provided with a circular hole 16 which is in communication with the flow channel 15 near the tail.

[0053] Referring again to Figure 1 As shown in the figure, there are two paths for the liquid in the shaft seal chamber to flow to the inlet of the stuffing 5, and the liquid resistance of the two paths is quite different: the first path is the annular gap between the stuffing box base 1 and the main shaft 14; the second path is the flow through the flow channel 15 on the stuffing box base 1 and the circular hole 16 on the valve body 8 to the inlet of the stuffing 5.

[0054] In path one, the inner wall of the plenum base 1 that mates with the main shaft 14 is machined with several toothed grooves, which mate with the main shaft 14 to form a labyrinth seal with a large liquid resistance. When the liquid flows through the tortuous labyrinth gap, a throttling effect is generated, thereby achieving the purpose of preventing leakage and reducing pressure. In contrast, path two has a larger overall flow area and a smaller liquid resistance.

[0055] When the unit operates normally within a certain frequency conversion range, the operating speed range is fixed. When the unit operates at the lowest speed within the frequency conversion range, the stuffing box 7 and stuffing gland 4 are adjusted downwards by adjusting screw 2 and fixing nut 3. The packing tightness is controlled by the actual leakage on site. At this time, the liquid movement trajectory inside the packing 5 is as follows: Figure 3 As indicated by the arrow, due to the low pressure in the shaft seal chamber, the liquid flows through the round hole on the valve body 8 to the end face area of ​​the valve body 8. The pressure acting on the end face of the valve body 8 cannot balance the elastic force generated by the spring 9. The valve body 8 remains stationary with the maximum opening. Path two is in the state of minimum liquid resistance. Therefore, most of the liquid will flow from the shaft seal chamber to the packing 5 sealing inlet along path two. At this time, the cavity pressure at the inlet of the packing 5 is approximately equal to the shaft seal chamber pressure, which means that the pressure at the inlet and outlet of the annular gap between the plenum base 1 and the main shaft 14 is almost equal. The liquid inside is almost in a state of radial rotation and no axial flow.

[0056] Assuming the pressure in the inlet chamber of packing 5 is P1, the leakage of packing 5 is Q1, and the flow area and flow coefficient of the sealing system formed by packing 5 and water seal ring 6 through compression are F, respectively. m1 The flow coefficient μ1, and the relationships between the above variables are as follows:

[0057] Q1 = P1 * F m1 *μ1

[0058] When the unit operates at its highest speed within the frequency conversion range, the packing 5 remains tightly compressed. Rotating the adjusting nut 13 pushes the stop block 12 to adjust the compression of the spring 9, thereby adjusting the opening of the valve body 8 and controlling the flow area of ​​path two, ensuring that the leakage of the packing 5 seal remains consistent with that at low speeds. At this time, the liquid movement trajectory within the packing 5 is as follows: Figure 4 As shown by the arrow, due to the high pressure in the shaft seal chamber, the liquid flows through the round hole 16 on the valve body 8 to the end face area of ​​the valve body 8. The elastic force generated by the pressure balance spring 9 on the end face of the valve body 8 pushes the valve body 8 to move to the right, the opening becomes smaller, the liquid resistance of path two increases, and the equilibrium state is that the liquid resistance of path two is approximately equal to that of path one. Therefore, the liquid will be subject to throttling and pressure reduction regardless of whether it passes through path one or path two.

[0059] Assuming that the packing 5 sealing inlet cavity pressure is P2 at this time, the packing 5 sealing leakage does not change, the sealing system formed by the packing 5 and the water seal ring 6 through the compression is consistent with the lowest speed, the flow area and the flow coefficient are equal to the low speed, so it can be inferred that P2 is equal to P1.

[0060] When the unit runs between the highest and lowest speed, the opening of the valve body 8 is dynamically adjusted by the mutual balance between the shaft seal chamber pressure and the balance spring 9, different liquid resistance is formed, the packing sealing inlet cavity is approximately in a constant pressure state, so as to cope with the limitation of variable speed on the use of packing seal.

[0061] Those skilled in the art of the present technology should realize that the above embodiments are only used to illustrate the present application, and are not used as a limitation on the present application, as long as the changes and modifications of the above described embodiments are within the scope of the spirit of the present application, they will fall within the scope of the claims of the present application.

Claims

1. A constant pressure packing seal, characterized by: The application relates to a packing box base, a packing cover, packing, a packing box and a pressure regulating mechanism. The packing box base is sleeved on the outer side of the main shaft and forms a shaft seal chamber with the main shaft, The inner side of the packing box base is provided with a plurality of tooth-shaped grooves and forms a labyrinth seal with the main shaft, The flow channel in the packing box base is in a circular hole shape, The packing box base is further provided with a mounting hole vertically penetrating the flow channel, The packing cover is sleeved on the outer side of the main shaft and is connected to the top of the packing box base, The packing is filled between the packing cover, the packing box base and the main shaft, The packing box is arranged on the outer side of the packing box base, The pressure regulating mechanism is arranged on the packing box base and cooperates with the flow channel in the packing box base, The pressure regulating mechanism comprises a valve body, a spring, a valve cover, a locking nut, a stop block and an adjusting nut, The valve body is coaxially arranged in the mounting hole, One end of the valve cover is arranged on the mounting hole to seal the mounting hole, The stop block is arranged on the other end of the valve cover, The spring is horizontally arranged in the valve cover and the mounting hole, one end of the spring is in contact with the valve body and the other end is in contact with the stop block, The adjusting nut is screwed on the other end of the valve cover through the locking nut, and the adjusting nut cooperates with the stop block, The valve body is provided with a circular hole communicating with the flow channel, The packing box base and the packing cover are connected through an adjusting screw and a fixing nut.

2. The constant pressure packing seal of claim 1, wherein: The packing, the packing box base and the main shaft are further provided with a water seal ring.

3. The constant pressure packing seal of claim 1, wherein: The packing box base, the packing cover, the packing and the packing box all adopt a split structure.

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