CN112665377A

CN112665377A - Rotary bell-jar furnace

Info

Publication number: CN112665377A
Application number: CN202011563012.7A
Authority: CN
Inventors: 欧阳建; 胡茂; 楚琪
Original assignee: Hunan Gold Furnace Science & Technology Co ltd
Current assignee: Hunan Gold Furnace Science & Technology Co ltd
Priority date: 2020-12-25
Filing date: 2020-12-25
Publication date: 2021-04-16

Abstract

The invention discloses a rotary bell jar furnace, which comprises a furnace body with a hearth and a furnace door for sealing the hearth, wherein a heating device is installed in the hearth, the hearth is connected with an air inlet system and an exhaust system, the air inlet system comprises a plurality of air inlet pipes which extend into the hearth and are arranged in an up-and-down extending manner, the plurality of air inlet pipes are arranged at intervals around the rotating axis of the furnace door, one end of each air inlet pipe is used as an air inlet end and is connected with an air source, air inlets which are communicated with the hearth and are sequentially arranged at intervals in the up-and-down direction are arranged on the pipe wall of each air inlet pipe, and the opening sizes of the plurality of air inlets are configured. The rotary bell-jar furnace has the advantages of simple structure, low cost, easy assembly and maintenance, stable and reliable work, good temperature and atmosphere uniformity and the like.

Description

Rotary bell-jar furnace

Technical Field

The invention relates to the technical field of heat treatment kilns, in particular to a rotary bell-jar furnace.

Background

In the field of new materials such as capacitors, electronic ceramics, powder metallurgy and the like, products are increasingly developed towards high-end, for example, MLCCs (multi-layer ceramic capacitors) are widely applied to various high-frequency and low-frequency capacitors, have the characteristics of high reliability, high precision, high integration, low power consumption, large capacity, small volume, low cost and the like, play roles of decoupling, coupling, filtering, bypassing, resonance and the like, and mainly develop towards miniaturization, high-capacity quantization, high-frequency transformation, high-temperature transformation and high-voltage transformation.

The sintering equipment for sintering the new materials generally adopts an electric heating kiln, and according to the sintering temperature and different products, an electric heating wire, a silicon carbide rod, a silicon molybdenum rod and the like can be used as heating elements. The whole sintering process comprises four processes of glue discharging, temperature rising, high temperature, heat preservation, sintering, temperature reduction and heat preservation tempering. With the development of new products and the application of new processes, higher requirements are put forward on sintering equipment, which is specifically shown in the following steps:

firstly, the oxygen content must be accurately controlled, which requires the cooperation of the whole gas distribution system, the gas inlet system, the gas outlet system and the furnace body sealing system;

secondly, the temperature uniformity needs to be guaranteed, and the cooperative matching of a heating system and an atmosphere system is needed.

However, in the air inlet system of the existing atmosphere rotary bell jar furnace, a plurality of air inlets are arranged on the peripheral side wall of the hearth to introduce air into the hearth, and the air outlet is arranged at the bottom of the hearth to discharge the air, so that the air inlet and outlet mode has poor uniformity of oxygen content and temperature in the hearth, and is difficult to achieve higher process requirements, especially when the required sintering temperature is higher (for example, the sintering temperature of MLCC is about 1600 ℃), under such conditions, only the silicon-molybdenum rod can be used as a heating element, but the silicon-molybdenum rod can only adopt a hoisting mode due to the material problem of the silicon-molybdenum rod, and the hoisting mode of the silicon-molybdenum rod can cause the temperature in the middle and periphery of the hearth and the temperature in the up-and-down direction to be more uneven.

Disclosure of Invention

The invention aims to solve the technical problem of overcoming the defects in the prior art and provides the rotary bell-jar furnace which is simple in structure, low in cost, easy to assemble and maintain, stable and reliable in work and good in temperature and atmosphere uniformity.

In order to solve the technical problems, the invention adopts the following technical scheme:

the utility model provides a rotation type bell jar stove, is including having furnace's furnace body and being used for sealing furnace's furnace gate, install heating device in the furnace, furnace is connected with air intake system and exhaust system, air intake system is including stretching into furnace and the many intake pipes that extend from top to bottom and arrange, many the intake pipe encircles the axis of rotation interval arrangement of furnace gate, and the one end of each intake pipe is connected with the air supply as the inlet end, is equipped with on the pipe wall of each intake pipe with furnace intercommunication and along the air inlet of upper and lower direction interval arrangement in proper order, and is a plurality of the opening size of air inlet configures into the flow of giving vent to anger unanimous or the basic unanimity of each air inlet when gaseous.

As a further improvement of the above technical solution:

the upper end of each air inlet pipe penetrates and extends out of the furnace body and is connected with the air source, and the opening areas of the plurality of air inlets on the air inlet pipes are reduced one by one along the direction from top to bottom.

The opening direction of the air inlet faces to the rotation axis of the oven door.

The furnace body is provided with an air box, each air inlet pipe is connected with the air box, and the air box is connected with an air source through a pipeline.

The furnace door comprises a door body, a rotary material bearing platform and a moving platform, wherein the rotary material bearing platform is rotatably arranged on the door body around an axis extending up and down, and the door body is supported and arranged on the moving platform through more than one elastic supporting piece.

Exhaust system includes many blast pipes that link to each other with exhaust apparatus, and each blast pipe stretches into from top to bottom in the furnace, each blast pipe be equipped with the more than one gas vent of furnace intercommunication, many the blast pipe encircles the axis of rotation interval arrangement of furnace gate, and the distance between the axis of rotation of every blast pipe to furnace gate is less than the distance between the axis of rotation of arbitrary one intake pipe to furnace gate.

The opening direction of the exhaust port is back to the rotation axis of the oven door.

Each blast pipe is equipped with a plurality of gas vents, and a plurality of gas vents are arranged along the direction from top to bottom at interval in proper order.

The exhaust device comprises a main exhaust pipe and an exhaust control assembly connected with the main exhaust pipe, each exhaust pipe is connected with the main exhaust pipe, the exhaust control assembly comprises two exhaust branch pipes, one end of each exhaust branch pipe is connected with the main exhaust pipe, the other end of each exhaust branch pipe is provided with an exhaust valve which is closed when the pressure is lower than the preset pressure so as to prevent exhaust and open exhaust when the pressure is higher than the preset pressure, and the preset pressure of the exhaust valve corresponding to the two exhaust branch pipes is different.

The exhaust valve comprises a valve body, a valve core and a telescopic cylinder arranged on the valve body, the valve body is provided with a valve cavity, an inlet communicated with the valve cavity and an outlet communicated with the valve cavity, the inlet is communicated with an exhaust branch pipe, the inner wall of the valve cavity is provided with an annular surface surrounding the inlet, and a telescopic rod of the telescopic cylinder is connected with the valve core and can drive the valve core to reciprocate between a first position where the inlet is disconnected with the valve cavity and a second position where the inlet is communicated with the valve cavity by attaching to the annular surface and separating from the annular surface.

Compared with the prior art, the invention has the advantages that:

the rotary bell jar furnace is characterized in that the gas inlet system adopts a plurality of gas inlet pipes, the gas inlet pipes are arranged at intervals around the rotating axis of the furnace door, the pipe wall of each gas inlet pipe is provided with gas inlets which are communicated with the furnace chamber and are sequentially arranged at intervals along the vertical direction, so that gas can enter the furnace chamber at a plurality of positions in the circumferential direction and the vertical direction of the furnace chamber, the gas inlet is more uniform, the uniformity of the temperature and the atmosphere in the furnace chamber is improved, meanwhile, the openings of the gas inlets on the pipe wall of each gas inlet pipe are configured to be consistent or basically consistent in the outlet flow of each gas inlet when the gas enters from one end of the gas inlet pipe, the inlet flow of each position is also consistent or basically consistent, the inlet uniformity can be further improved, and the uniformity of. The rotary bell-jar furnace also has the advantages of simple structure, low cost, easy assembly and maintenance, and stable and reliable work.

Drawings

FIG. 1 is a perspective view of a rotary bell jar furnace.

FIG. 2 is a schematic main sectional structure view of the furnace body.

FIG. 3 is a schematic top view of the furnace body.

Fig. 4 is a front view structural diagram of the intake pipe.

Fig. 5 is a front view of the exhaust pipe.

Fig. 6 is a schematic perspective view of the exhaust apparatus.

Fig. 7 is a sectional view schematically showing the exhaust valve when closed.

Fig. 8 is a sectional structure view of the discharge valve when it is opened.

Fig. 9 is a main sectional structural view of the oven door.

Illustration of the drawings:

1. a furnace body; 11. a hearth; 2. a furnace door; 21. a door body; 22. rotating the material bearing platform; 23. a mobile platform; 24. an elastic support member; 3. a heating device; 4. an air intake system; 41. an air inlet pipe; 411. an air inlet; 42. a gas tank; 5. an exhaust system; 51. an exhaust pipe; 511. an exhaust port; 52. an exhaust main pipe; 53. an exhaust branch pipe; 6. an exhaust valve; 61. a valve body; 611. a valve cavity; 612. an inlet; 613. an outlet; 614. an annular face; 62. a valve core; 63. a telescopic cylinder.

Detailed Description

The invention is described in further detail below with reference to the figures and specific examples.

As shown in fig. 1 to 4, the rotary bell jar furnace of the present embodiment includes a furnace body 1 having a furnace chamber 11 and a furnace door 2 for closing the furnace chamber 11, the lower end opening of the furnace chamber 11 drives the furnace door 2 to move up and down to open and close the lower end opening of the furnace chamber 11, a heating device 3 is installed in the furnace chamber 11, the furnace chamber 11 is connected with an air intake system 4 and an exhaust system 5, the air intake system 4 includes a plurality of air intake pipes 41 extending into the furnace chamber 11 and arranged in an up-down extending manner, the plurality of air intake pipes 41 are arranged around a rotation axis of the furnace door 2 at intervals, one end of each air intake pipe 41 is connected with an air source as an air intake end, an air inlet 411 communicated with the furnace chamber 11 and arranged at intervals in an up-down direction is arranged on a pipe wall of each air intake pipe 41, and the opening sizes of. In the rotary bell jar furnace, the air inlet system 4 adopts a plurality of air inlet pipes 41, the plurality of air inlet pipes 41 are arranged at intervals around the rotating axis of the furnace door 2, air inlets 411 which are communicated with the furnace chamber 11 and are arranged at intervals along the up-down direction are arranged on the pipe wall of each air inlet pipe 41, gas can enter the furnace chamber 11 at a plurality of positions in the circumferential direction and the up-down direction of the furnace chamber 11, thereby leading the air inlet to be more uniform, being beneficial to improving the uniformity of the temperature and the atmosphere in the furnace chamber 11, simultaneously, the opening sizes of the plurality of air inlets 411 on the pipe wall of each air inlet pipe 41 are configured to be consistent or basically consistent with the air outlet flow of each air inlet 411 when the gas enters from one end of the air inlet pipe 41, leading the air inlet flow at each position to be consistent or basically consistent. The rotary bell-jar furnace also has the advantages of simple structure, low cost, easy assembly and maintenance, and stable and reliable work.

In another embodiment, a plurality of air inlet pipes 41 are preferably arranged at regular intervals around the rotation axis of the oven door 2, and a further preferred number of air inlet pipes 41 is six.

In this embodiment, the upper end of each air inlet pipe 41 penetrates and extends out of the furnace body 1 and is connected with an air source, the opening areas of the plurality of air inlets 411 on each air inlet pipe 41 are reduced one by one along the direction from top to bottom, the opening area of the upper air inlet 411 is large, the opening area of the lower air inlet 411 is small, when air enters the air inlet pipe 41 from the upper end of the air inlet pipe 41, the air can preferentially enter the hearth 11 from the lower air inlet 411 under the action of airflow inertia, and therefore the air outlet flow of each air inlet 411 is consistent or basically consistent when the air enters from the upper end of the air inlet pipe 41. This is achieved by merely arranging the opening area of each intake port 411, and has the advantages of a simple and compact structure, easy manufacturing, and low cost. In the embodiment, the upper end of each air inlet pipe 41 penetrates through and extends out of the furnace body 1 and is connected with the air source, so that the installation of the air inlet pipes 41 is facilitated, the air inlet pipes 41 are fixed relative to the furnace body 1, the connection with the air source is facilitated, and the sealing is easily ensured.

In this embodiment, the opening direction of the air inlet 411 faces the rotation axis of the furnace door 2, so that the air entering the hearth 11 flows to the material loaded on the furnace door 2, and is beneficial to fully and uniformly contacting the material, especially when the furnace door 2 drives the material to rotate, the contact between the material and the air is more fully and uniformly.

In this embodiment, the furnace body 1 is provided with an air box 42, each air inlet pipe 41 is connected with the air box 42, and the air box 42 is connected with an air source through a pipeline. Set up gas tank 42, the heat of usable furnace body 1 preheats gas on the one hand, realizes preheating the utilization, reduces the energy consumption, and on the other hand gas tank 42 plays the effect that reduces the gas velocity of flow, makes gas flow velocity slow down behind gas tank 42, slowly gets into furnace 11 through intake pipe 41 afterwards, can make atmosphere and temperature more even in the furnace 11. In another embodiment, the air box 42 is preferably annular to facilitate connection to each air inlet conduit 41. In another embodiment, the gas box 42 is preferably arranged on the top of the furnace body 1 and is attached to the furnace body 1, so that the preheating utilization is more facilitated due to the higher temperature of the furnace top.

In this embodiment, as shown in fig. 1 and 9, the oven door 2 includes a door body 21, a rotary material receiving platform 22 and a moving platform 23, the rotary material receiving platform 22 is rotatably mounted on the door body 21 around an axis extending up and down, and the door body 21 is supported and mounted on the moving platform 23 by a plurality of elastic supporting members 24. On one hand, the elastic supporting part 24 allows the door body 21 to move downwards relative to the moving platform 23, and plays a role of elastic buffering in the process that the moving platform 23 drives the door body 21 to move from bottom to top to seal the hearth 11, so that the door body 21 can be prevented from excessively pressing the furnace body 1, damage to the door body 21 and the furnace body 1 and damage to sealing parts between the door body 21 and the furnace body 1 can be avoided, and on the other hand, the door body 21 can swing relative to the moving platform 23 under the action of the elastic supporting part 24, so that the levelness of the door body 21 can be automatically adjusted, the door body 21 can always keep the best fit state with the furnace body 1, and the sealing performance and the safety reliability are. From another point of view, in the case of achieving the above object, the performance requirements of the drive device for driving the movement of the oven door 2 can be reduced. The resilient support members 24 are preferably telescopic springs, and a plurality of resilient support members 24 are preferably evenly spaced about the axis of the rotary material support platform 22. In another embodiment, the door body 21 may also be supported and mounted on the moving platform 23 by only one elastic support 24.

In this embodiment, as shown in fig. 2, 3 and 5, the exhaust system 5 includes a plurality of exhaust pipes 51 connected to the exhaust device, each exhaust pipe 51 extends into the furnace 11 from top to bottom, each exhaust pipe 51 is provided with more than one exhaust opening 511 communicated with the furnace 11, the plurality of exhaust pipes 51 are arranged around the rotation axis of the furnace door 2 at intervals, and the distance between each exhaust pipe 51 and the rotation axis of the furnace door 2 is smaller than the distance between any one of the intake pipes 41 and the rotation axis of the furnace door 2. This exhaust system 5 makes the gaseous furnace 11 of 11 ascending a plurality of positions discharge 11 of 11 circumference in furnace, does benefit to the homogeneity that improves temperature and atmosphere in the furnace 11, does benefit to gaseous smooth and easy, timely, quick discharge simultaneously. Meanwhile, as the air flow in the hearth 11 moves in a vortex mode when the furnace door 2 rotates, a plurality of exhaust pipes 51 are arranged at intervals around the rotating axis of the furnace door 2, and the distance between each exhaust pipe 51 and the rotating axis of the furnace door 2 is smaller than the distance between any one air inlet pipe 41 and the rotating axis of the furnace door 2, the exhaust gas can be rapidly discharged by means of the vortex-mode air flow, and the exhaust efficiency is improved. In another embodiment, it is preferred that a plurality of exhaust ducts 51 are arranged evenly spaced around the axis of rotation of the oven door 2.

In this embodiment, the opening direction of the exhaust port 511 is opposite to the rotation axis of the oven door 2, which is more advantageous for rapidly exhausting the exhaust gas by the air flow in the form of vortex.

In this embodiment, each exhaust pipe 51 is provided with a plurality of exhaust ports 511, and the plurality of exhaust ports 511 are sequentially arranged at intervals along the direction from top to bottom. The gas in the hearth 11 is discharged out of the hearth 11 at a plurality of positions in the circumferential direction and the up-down direction of the hearth 11, and the uniformity of the temperature and the atmosphere in the hearth 11 is improved. Preferably, the number of the exhaust pipes 51 is three.

In the present embodiment, as shown in fig. 6 to 8, the exhaust device includes an exhaust main pipe 52 and an exhaust control assembly connected to the exhaust main pipe 52, each exhaust pipe 51 is connected to the exhaust main pipe 52, the exhaust control assembly includes two exhaust branch pipes 53, one end of each exhaust branch pipe 53 is connected to the exhaust main pipe 52, the other end of each exhaust branch pipe 53 is provided with an exhaust valve 6 which is closed when the pressure is lower than a preset pressure to prevent exhaust and is opened when the pressure is higher than the preset pressure, and the preset pressures of the exhaust valves 6 corresponding to the two exhaust branch pipes 53 are different. That is, the preset pressure of the exhaust valve 6 corresponding to one of the exhaust branch pipes 53 is greater than the preset pressure of the exhaust valve 6 corresponding to the other exhaust branch pipe 53, the exhaust device can realize that the exhaust valve 6 with lower preset pressure is used for normal exhaust to reduce the furnace pressure to the preset value, and when the exhaust speed of the exhaust valve 6 with lower preset pressure still cannot reduce the furnace pressure to the preset value, the raised furnace pressure can force the exhaust valve 6 with higher preset pressure to open for synchronous exhaust, thereby ensuring accurate, stable and reliable automatic adjustment of the furnace pressure.

In this embodiment, the exhaust valve 6 includes a valve body 61, a valve core 62 and a telescopic cylinder 63 mounted on the valve body 61, the valve body 61 is provided with a valve cavity 611, an inlet 612 communicated with the valve cavity 611 and an outlet 613 communicated with the valve cavity 611, the inlet 612 is communicated with the exhaust branch pipe 53, the inner wall of the valve cavity 611 is provided with an annular surface 614 surrounding the inlet 612, and the telescopic rod of the telescopic cylinder 63 is connected with the valve core 62 and can drive the valve core 62 to reciprocate between a first position where the valve core 62 is attached to the annular surface 614 to disconnect the inlet 612 from the valve cavity 611 and a second position where the valve core is detached from the annular surface 614 to communicate the inlet 612 with the valve. When the exhaust valve 6 is closed, the telescopic cylinder 63 drives the valve core 62 to be attached to the annular surface 614, and the valve core 62 disconnects the inlet 612 from the valve cavity 611 (see fig. 7), so that no exhaust is performed; in the closed state, if the acting force of the gas from the exhaust branch pipe 53 to the inlet 612 on the valve core 62 is greater than the acting force of the driving gas from the telescopic cylinder 63 on the telescopic rod (at this time, the pressure of the gas from the exhaust branch pipe 53 to the inlet 612 is a preset pressure), the valve core 62 is forced to move to the second position (see fig. 8) against the acting force of the driving gas in the telescopic cylinder 63, the valve core 62 is separated from the annular surface 614, the inlet 612 is communicated with the valve cavity 611, and the gas in the exhaust branch pipe 53 can be exhausted through the inlet 612, the valve cavity 611 and the outlet 613, so that the exhaust is. Meanwhile, when the telescopic cylinder 63 drives the valve core 62 to separate from the annular surface 614, normally open exhaust can be realized. The exhaust valve 6 adopts the telescopic cylinder 63 to control the valve core 62 to move to realize opening and closing, the force of the valve core 62 clinging to the annular surface 614 can be controlled by controlling the pressure of the telescopic cylinder 63, the preset pressure for opening the exhaust valve 6 can also be controlled by controlling the pressure of the telescopic cylinder 63, and the exhaust valve is simple and convenient to control, convenient to adjust, high in precision and stable and reliable in work.

In this embodiment, the heating device 3 and the air intake system 4 are both set with reference to an existing rotary bell jar furnace, for example, the heating device 3 adopts a silicon carbide rod or a silicon molybdenum rod, the air intake system 4 includes a plurality of air intake pipelines communicated with the furnace 11, and the air intake pipelines are connected with an air supply source.

The above description is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above-described embodiments. Modifications and variations that may occur to those skilled in the art without departing from the spirit and scope of the invention are to be considered as within the scope of the invention.

Claims

1. The utility model provides a rotation type bell jar furnace, is including furnace body (1) that has furnace (11) and be used for sealing furnace gate (2) of furnace (11), install heating device (3) in furnace (11), furnace (11) are connected with air intake system (4) and exhaust system (5), its characterized in that: intake system (4) are including stretching into many intake pipe (41) that furnace (11) and upper and lower extension were arranged, many intake pipe (41) encircle the axis of rotation interval arrangement of furnace door (2), the one end of each intake pipe (41) is connected with the air supply as the inlet end, is equipped with on the pipe wall of each intake pipe (41) with furnace (11) intercommunication and along upper and lower direction interval arrangement's air inlet (411) in proper order, and is a plurality of the opening size of air inlet (411) configures into the flow of giving vent to anger of each air inlet (411) unanimously or unanimous basically when gaseous by intake pipe (41) one end is advanced.

2. The rotary bell jar furnace of claim 1 wherein: the upper end of each air inlet pipe (41) penetrates through and extends out of the furnace body (1) and is connected with the air source, and the opening areas of the plurality of air inlets (411) on each air inlet pipe (41) are reduced one by one along the direction from top to bottom.

3. The rotary bell jar furnace of claim 2 wherein: the opening direction of the air inlet (411) faces to the rotation axis of the oven door (2).

4. The rotary bell jar furnace of claim 1 wherein: the furnace body (1) is provided with an air box (42), each air inlet pipe (41) is connected with the air box (42), and the air box (42) is connected with an air source through a pipeline.

5. The rotary bell jar furnace of claim 1 wherein: the furnace door (2) comprises a door body (21), a rotary material bearing platform (22) and a moving platform (23), wherein the rotary material bearing platform (22) is rotatably arranged on the door body (21) around an axis extending up and down, and the door body (21) is supported and arranged on the moving platform (23) through more than one elastic supporting piece (24).

6. The rotary bell jar furnace of any one of claims 1 to 5 wherein: exhaust system (5) include many blast pipes (51) that link to each other with exhaust apparatus, and each blast pipe (51) stretches into from top to bottom in furnace (11), each blast pipe (51) are equipped with more than one gas vent (511) with furnace (11) intercommunication, many blast pipe (51) encircle the axis of rotation interval arrangement of furnace door (2), and every blast pipe (51) are less than the distance between the axis of rotation of arbitrary one intake pipe (41) to furnace door (2) to the axis of rotation of furnace door (2).

7. The rotary bell jar furnace of claim 6 wherein: the opening direction of the air outlet (511) is back to the rotation axis of the oven door (2).

8. The rotary bell jar furnace of claim 6 wherein: each exhaust pipe (51) is provided with a plurality of exhaust ports (511), and the exhaust ports (511) are sequentially arranged at intervals along the direction from top to bottom.

9. The rotary bell jar furnace of claim 6 wherein: the exhaust device comprises a main exhaust pipe (52) and an exhaust control assembly connected with the main exhaust pipe (52), each exhaust pipe (51) is connected with the main exhaust pipe (52), the exhaust control assembly comprises two exhaust branch pipes (53), one end of each exhaust branch pipe (53) is connected with the main exhaust pipe (52), the other end of each exhaust branch pipe (53) is provided with an exhaust valve (6) which is closed when the other end is lower than preset pressure to prevent exhaust and is opened when the other end is higher than the preset pressure, and the preset pressure of the exhaust valve (6) corresponding to the two exhaust branch pipes (53) is different.

10. The rotary bell jar furnace of claim 9 wherein: the exhaust valve (6) comprises a valve body (61), a valve core (62) and a telescopic cylinder (63) installed on the valve body (61), the valve body (61) is provided with a valve cavity (611), an inlet (612) communicated with the valve cavity (611) and an outlet (613) communicated with the valve cavity (611), the inlet (612) is communicated with the exhaust branch pipe (53), the inner wall of the valve cavity (611) is provided with an annular surface (614) surrounding the inlet (612), the telescopic rod of the telescopic cylinder (63) is connected with the valve core (62), and can drive the valve core (62) to reciprocate between a first position where the annular surface (614) is attached to enable the inlet (612) to be disconnected with the valve cavity (611) and a second position where the annular surface (614) is separated to enable the inlet (612) to be communicated with the valve cavity (611).