CN211525610U

CN211525610U - Four-way valve

Info

Publication number: CN211525610U
Application number: CN201921664970.6U
Authority: CN
Inventors: 熊匀均
Original assignee: Dunan Environment Technology Co Ltd
Current assignee: Dunan Environment Technology Co Ltd
Priority date: 2019-09-30
Filing date: 2019-09-30
Publication date: 2020-09-18
Anticipated expiration: 2029-09-30

Abstract

The utility model discloses a four-way valve, which comprises a valve body, a valve core and a driving mechanism, wherein the valve core is rotatably arranged in the valve body; the driving mechanism can drive the valve core to rotate in the valve body; one end of the valve core is provided with a rotary driving part, the other end of the valve core is provided with a rotary supporting part, and the valve core is rotatably arranged on the valve body through the rotary supporting part; and the rotating shaft part of the driving mechanism is matched with the rotary driving part of the valve core and is used for driving the valve core to rotate in the valve body. The utility model discloses the rotatory drive division on the available case realizes the case location from top to bottom in the valve body with the assembly of rotation support portion to this direction matching between save case and the valve body, and the assembly clearance between case and the valve body on the multiplicable this cross valve, the assembly clearance between case and the valve body is big moreover, can prevent to cause the dead situation of card to take place because of the entering of impurity between case and the valve body, has the effect that improves this cross valve job stabilization nature.

Description

Four-way valve

Technical Field

The utility model belongs to the technical field of the flow switches is relevant, especially, relate to a cross valve.

Background

The four-way valve is a control valve with four valve ports, is an indispensable component in refrigeration equipment, and is used for realizing the conversion function of refrigeration and heating in a refrigeration system. The four-way valve applied to the automobile generally adopts a rotary four-way reversing valve structure, and when the four-way valve works, the stator is matched with the rotor, so that the rotor can be driven to rotate, and the rotating rotor can drive the valve core to rotate in the valve body under the transmission of the transmission mechanism, so that the communication between the four valve ports on the valve body is switched.

At present, a valve core on the existing four-way valve is directly assembled into a valve body, the peripheral wall of the valve core needs to be attached to the inner wall of the valve body, so that the peripheral wall of the valve core needs to be matched with the inner wall of the valve body, namely, the valve core and the valve body on the existing four-way valve need to be guided and matched; in addition, because the peripheral wall of case pastes on the inner wall of valve body for the fitting gap between case and the valve body is little, in case there is impurity entering to take place the card easily to die between case and the valve body like this, thereby causes the holistic damage of this cross valve.

SUMMERY OF THE UTILITY MODEL

In view of this, it is necessary to provide a four-way valve in order to solve the technical problems in the prior art.

The four-way valve comprises a valve body with four valve ports, a valve core and a driving mechanism, wherein the valve core is rotatably arranged in the valve body; the driving mechanism can drive the valve core to rotate in the valve body; one end of the valve core is provided with a rotary driving part, the other end of the valve core is provided with a rotary supporting part, the valve core is rotatably arranged on the valve body through the rotary supporting part, and a rotating shaft part of the driving mechanism is matched with the rotary driving part of the valve core and is used for driving the valve core to rotate in the valve body; the valve core is provided with a first flow channel and a second flow channel, the first flow channel is communicated with two of the valve ports on the valve body and forms a high-pressure cavity of the four-way valve, the second flow channel is communicated with the other two valve ports on the valve body and forms a low-pressure cavity of the four-way valve, a gap is reserved between the valve core and the valve body, and when the gap distance between the valve core at the high-pressure cavity side and the valve body is the largest, the gap distance between the valve core at the low-pressure cavity side and the valve body is the smallest.

As a preferred embodiment of the present invention, the circle center line of the rotation driving portion and the circle center line of the rotation supporting portion are disposed on the same straight line.

As a preferable aspect of the present invention, the end surface of the valve element on which the rotation driving portion is provided is a planar structure.

As the preferred embodiment of the present invention, the rotation driving portion is set as a connection boss, and the rotation shaft portion of the driving mechanism is inserted into the connection boss, and is matched with the key groove of the connection boss.

As the preferred scheme of the utility model, be used for on the connection boss with last pivot portion complex spread groove extends to the inside of case.

As the utility model discloses an optimal scheme, the case is being equipped with spacing arc groove has been seted up on the terminal surface of rotary drive portion, the last spacing axle that is equipped with of actuating mechanism, spacing axle part insert to the spacing arc inslot of case, actuating mechanism passes through spacing axle with cooperation between the spacing arc groove is right the rotary drive of case carries on spacingly.

As the utility model discloses a preferred scheme, be equipped with on the valve body and support cooperation portion, the case passes through the rotation support portion with support cooperation between the cooperation portion rotationally connect in the valve body.

As a preferred embodiment of the present invention, the rotation supporting portion is a circular hole formed on the valve element, and a circular center line of the circular hole and a circular center line of the valve element are arranged on the same straight line; the supporting matching part is a supporting convex column on the valve body, and the supporting convex column upwards extends into the round hole of the valve core.

As a preferable aspect of the present invention, the end surface of the valve element on which the rotation supporting portion is provided is a planar structure.

As the utility model discloses a preferred scheme, be fixed with the gasket bracket on the valve body, actuating mechanism's pivot portion runs through the gasket bracket and with the rotatory drive section keyway cooperation of case.

Because of above-mentioned technical scheme's application, compared with the prior art, the utility model have the following advantage:

the utility model provides a cross valve, the rotation driving part on the available case realizes case location from top to bottom in the valve body with the assembly of rotation support portion, with this direction matching between save case and the valve body, and the fit-up gap between case and the valve body on the multiplicable this cross valve, and fit-up gap between case and the valve body is big, prevent that the case from taking place wearing and tearing when the valve body internal rotation and between the valve body, can prevent to cause the dead situation of card to take place because of the entering of impurity between case and the valve body, have the effect that improves this cross valve job stabilization nature.

Drawings

Fig. 1 is a schematic structural diagram of a four-way valve according to an embodiment of the present invention.

Fig. 2 is a cross-sectional view of a four-way valve according to an embodiment of the present invention.

Fig. 3 is a schematic diagram of a working principle of a four-way valve according to an embodiment of the present invention.

Fig. 4 is an enlarged view of a portion P in fig. 3.

Fig. 5 is a schematic structural diagram of the middle valve element of the present invention.

Fig. 6 is a sectional view of the middle valve element of the present invention.

Fig. 7 is a schematic structural view of the middle gasket bracket of the present invention.

Fig. 8 is an assembly diagram of the rotor and the driving wheel of the present invention.

Fig. 9 is a schematic structural view of the rotor of the present invention.

Fig. 10 is a schematic structural view of the driving wheel of the present invention.

10, a valve body; 11. a first valve port; 12. a second valve port; 13. a third valve port; 14. a fourth valve port; 100. a valve cavity; 101. a gasket; 102. a support boss; 103. a gasket carrier; 1031. a bracket body; 1032. a limiting convex part; 20. a valve core; 21. connecting the bosses; 211. connecting grooves; 22. a limiting arc groove; 23. a circular hole; 201. a first flow passage; 202. a second flow passage; 30. a drive mechanism; 31. a stator; 32. A rotor; 321. a protrusion; 322. a ring groove; 33. a driving wheel; 331. a groove; 332. connecting the convex plate; 34. A driven wheel; 35. a gear drive assembly; 301. a rotating shaft part; 40. a valve cover; 41. and a bearing.

Detailed Description

The technical solutions in the embodiments of the present invention will be described clearly and completely with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments in the present invention, all other embodiments obtained by a person skilled in the art without creative work belong to the protection scope of the present invention.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

Referring to fig. 1 to 10, a four-way valve according to an embodiment of the present invention includes a valve body 10 having four valve ports, a valve core 20 rotatably disposed in the valve body 10, and a driving mechanism 30.

In the present embodiment, the valve core 20 is a spherical structure, one end of the valve core 20 is provided with a rotation driving portion, and the other end of the valve core 20 is provided with a rotation supporting portion, the valve core 20 is rotatably disposed on the valve body 10 through the rotation supporting portion, and the rotation driving portion of the valve core 20 is engaged with the rotation shaft portion 301 of the driving mechanism 30 for driving the valve core 20 to rotate in the valve body 10. That is to say, the valve core 20 of the present embodiment is specifically assembled in the valve body 10 through the rotation supporting portion and the rotation driving portion, so as to achieve the vertical positioning of the valve core 20 assembled on the valve body 10, so that the valve core 20 of the present embodiment is assembled in the valve body 10 without a guiding structure in the circumferential direction, so as to expand the assembly gap between the valve core 20 and the valve body 10, and to avoid the occurrence of the situation that the impurities enter between the valve core 20 and the valve body 10 and then cause the seizure.

The circle center line of the rotation driving portion and the circle center line of the rotation supporting portion are arranged on the same straight line and are collinear with the circle center line of the valve core 20, so that the rotation shaft portion 301 of the driving mechanism 30 and the valve core 20 rotate in the same direction, and therefore the assembly between the rotation shaft portion 301 of the driving mechanism 30 and the rotation driving portion of the valve core 20 is facilitated.

In the present embodiment, the end surface of the valve core 20 on which the rotation driving portion is disposed is a planar structure, so that the rotation driving portion is disposed on the valve core 20, and the production and preparation of the entire structure of the valve core 20 are facilitated.

Specifically, the rotation driving portion is provided as a connection boss 21, and the rotating shaft portion 301 of the driving mechanism 30 is inserted into the connection boss 21 and is in key-groove fit with the connection boss 21, so that the rotating shaft portion 301 of the driving mechanism 30 and the valve body 20 can be easily attached and detached. The rotary driving part is not limited to the coupling boss 21 shown in the drawing, and a person skilled in the art may directly open a coupling groove for key-groove engagement with the rotary shaft part 301 of the driving mechanism 30 on the valve body 20 according to the use requirement.

Further, the connection groove 211 on the connection boss 21, which is used for being matched with the upper rotating shaft 301 of the driving mechanism 30, extends to the inside of the valve core 20, so that the rotating shaft 301 of the driving mechanism 30 can pass through the connection boss 21 downwards and be inserted into the valve core 20, thereby ensuring the stability of circumferential limiting of the rotating shaft 301 of the driving mechanism 30 and the valve core 20, and simultaneously having the function of shortening the axial length of the connection boss 21.

As a preferred embodiment of the present invention, the valve core 20 of the present embodiment is provided with the limiting arc groove 22 is further provided on the end surface of the connecting boss 21, correspondingly, the driving mechanism 30 is provided with a limiting shaft (not shown), the limiting shaft is partially inserted into the limiting arc groove 22 of the valve core 20, and the driving mechanism 30 passes through the limiting shaft and the matching between the limiting arc grooves 22 is right to limit the rotation driving of the valve core 20. It should be noted that the limiting shaft on the driving mechanism 30 is fixed relative to the rotating shaft portion 301, and specifically, the limiting shaft may be fixed on the gear box body of the driving mechanism 30, so that when the rotating shaft portion 301 of the driving mechanism 30 drives the valve element 20 to rotate in the valve body 10, the limiting arc groove 22 of the valve element 20 makes a rotational motion relative to the limiting shaft, and the rotational limiting of the valve element 20 is realized by the abutting between the limiting shaft and the groove walls at the two ends of the limiting arc groove 22.

The central angle of the arc-limiting groove 22 is 90 °, so that the rotating shaft 301 of the driving mechanism 30 can drive the valve core 20 to rotate 90 ° in the valve body 10, and the switching between two connecting passages on the four-way valve is realized.

In the present embodiment, the valve body 10 is provided with a support engagement portion, and the valve body 10 is rotatably connected to the valve body 20 by engagement between the rotation support portion and the support engagement portion.

Specifically, the rotary supporting portion is a circular hole 23 formed in the valve core 20, a circle center line of the circular hole 23 and a circle center line of the valve core 20 are arranged on the same straight line, the supporting matching portion is a supporting convex column 102 on the valve body 10, and the supporting convex column 102 extends upwards into the circular hole 23 of the valve core 20, so that the rotary connection between the valve core 20 and the valve body 10 is realized. It should be noted that the rotation supporting portion and the supporting matching portion are not limited to those shown in the drawings, and those skilled in the art can set the rotation supporting portion as a supporting convex column according to the use requirement, and the supporting matching portion is correspondingly set as a circular hole matched with the supporting convex column, and the valve core 20 is not limited to set a circular hole as the rotation supporting portion, and may also set a conical hole on the valve core 20 according to the use requirement.

Further, the end surface of the valve core 20 on which the rotation support portion is provided is also provided with a planar structure, so that a circular hole 23 is processed and formed on the valve core 20.

It can be understood that two flow passages are opened on the valve element 20 of the present embodiment, and the valve element 20 is disposed in the valve body 10, and the two flow passages on the valve element 20 can be respectively communicated with two of the valve ports on the valve body 10, and form two connection passages on the four-way valve. The valve body 20 of the present embodiment is a metal valve body.

Wherein, the first flow channel 201 is communicated with two valve ports on the valve body 10 and forms a high pressure cavity of the four-way valve; the second flow path 202 is connected to the other two ports of the valve body 10 and forms a low pressure chamber of the four-way valve. A gap is reserved between the valve core 20 and the valve body 10, and when the gap distance between the valve core 20 and the valve body 10 on the high pressure chamber side is the largest, the gap distance between the valve core 20 and the valve body 10 on the low pressure chamber side is the smallest. The high-pressure cavity on the four-way valve of the embodiment is always positioned at the outer side of the valve core 20, and the high-pressure cavity and the low-pressure cavity are arranged oppositely, so that the damage of parts in the four-way valve caused by the impact of instantaneous high pressure can be avoided in the process that the valve core 20 rotates in the valve body 10.

The four ports of the present embodiment are respectively defined as a first port 11, a second port 12, a third port 13 and a fourth port 14, wherein the first port 11 can communicate with the second port 12 or the fourth port 14 through the first flow channel 201, and the third port 13 can communicate with the fourth port 14 or the second port 12 through the second flow channel 202. That is, the drive mechanism 30 of the present embodiment can switch the two connection paths by rotating the valve body 20 in the valve body 10. The first port 11, the second port 12, the third port 13, and the fourth port 14 are provided on four end surfaces of the valve body 10, respectively.

As a preferable embodiment of the present invention, the valve body 10 is provided with a sealing pad 101 at the position of the second port 12, the third port 13 and the fourth port 14. When the four-way valve of the present embodiment is applied to a vehicle air conditioning system, a refrigerant does not leak at the positions of the second valve port 12, the third valve port 13, and the fourth valve port 14, thereby ensuring the sealing effect of two connecting passages on the four-way valve. The first valve port 11 serves as a refrigerant inlet.

In the present embodiment, a packing holder 103 is fixed to the valve body 10, and the rotary shaft portion 301 of the drive mechanism 30 penetrates the packing holder 103 and engages with the rotary drive portion of the valve body 20. The gasket bracket 103 is detachably connected to the valve body 10 by a screw (not shown), and in this embodiment, the valve core 20 may be first placed in the valve cavity 100 formed inward of the valve body 10, and then the gasket bracket 103 is covered on the valve body 10 and fixed by the screw, so that the valve core 20 is conveniently assembled in the valve cavity 100 of the valve body 10.

The gasket bracket 103 of the present embodiment includes a bracket body 1031 fixedly connected to the valve body 10, and a limiting protrusion 1032 provided on the bracket body 1031, where the limiting protrusion 1032 partially extends into the valve cavity 100 of the valve body 10, and a portion of the limiting protrusion 1032 extending into the valve cavity 100 abuts against three gaskets 101, so that the three gaskets 101 are always kept on the valve element 20 under the limitation of the limiting protrusion 1032 on the gasket bracket 103, and thus when the gasket 101 is impacted by the high pressure cavity pressure on the valve element 20, the limiting protrusion 1032 on the gasket bracket 103 can limit and support the gasket 103, and further the strength of the gasket 103 is increased, and the gasket 103 is prevented from deforming in the circumferential direction.

The driving mechanism 30 is used for driving the valve core 20 to rotate in the valve body 10, so that two connecting passages formed by matching four valve ports on the valve body 10 with the first flow passage 201 and the second flow passage 202 on the valve core 20 are switched.

In the present embodiment, the driving mechanism 30 includes a stator 31, a rotor 32 engaged with the stator 31, a driving wheel 33, a driven wheel 34, and a gear assembly 35 for connecting the driving wheel 33 and the driven wheel 34. The rotating shaft 301 of the driving mechanism 30 is fixed on the driven wheel 34, the driving wheel 33 is fixedly connected with the rotor 32, the rotor 32 is matched with the stator 31 to drive the driving wheel 33 to rotate, and the rotating driving wheel 33 can drive the valve core 20 to rotate through the gear transmission assembly 35 and the driven wheel 34. It should be noted that the cooperation between the stator 31 and the rotor 32 can be realized by controlling the on/off of the coil on the stator 31, and the on/off of the coil can cause the magnetic induction lines to change, and the rotor 32 is driven to rotate by the magnetic induction lines.

The driving wheel 33 and the rotor 32 are integrally formed by injection molding, so that the driving mechanism 30 on the four-way valve of the embodiment has a simple structure, the assembly process is simplified, and the assembly efficiency is improved; in addition, the driving wheel 33 and the rotor 32 are formed by integral injection molding, and the driving wheel 33, the gear transmission assembly 35 and the driven wheel 34 are sequentially meshed, so that the structural reliability of the driving mechanism 30 on the four-way valve is improved, the axial movement of the driving wheel is prevented, the situation that the driving wheel 33 falls off is avoided, and the effect of reducing the overall production cost of the four-way valve is achieved. It should be noted that the driving wheel 33 and the rotor 32 are not limited to be connected and fixed in an integrally injection molding direction, and those skilled in the art may also use welding, a close fit manner or other manners to connect and fix according to the use requirement.

In the four-way valve of this embodiment, a concave-convex matching structure is disposed at a position where the driving wheel 33 is connected to the rotor 32, and the rotor 32 can drive the driving wheel 33 to rotate through the concave-convex matching structure. When the rotor 32 drives the driving wheel 33 to rotate, the concave-convex matching structure between the rotor 32 and the driving wheel 33 is stressed to realize the rotation driving of the driving wheel 33, so that the position where the driving wheel 33 is connected with the rotor 32 is prevented from being disengaged.

Specifically, the concave-convex matching structure includes a groove 331 formed on the driving wheel 33 and a protrusion 321 formed on the inner wall of the rotor 32, the groove 331 and the protrusion 321 are correspondingly disposed, wherein the portion of the driving wheel 33, on which the groove 331 is formed, is inserted into the rotor 32 and is matched with the protrusion 321 on the rotor 32.

Further, a connecting convex plate 332 is arranged on one side end of the driving wheel 33, and a groove 331 on the driving wheel 33 is arranged on the outer peripheral surface of the connecting convex plate 332; the inner wall of the rotor 32 is provided with a circular groove 322 for matching with the connecting convex plate 332 on the driving wheel 33, wherein the protrusion 321 is arranged at the bottom position of the circular groove 331 on the rotor 32. When the driving wheel 33 is assembled and connected with the rotor 32, the connecting convex plate 332 on the driving wheel 33 is arranged in the ring groove 322 of the rotor 32, so as to prevent the axial movement of the driving wheel 33 assembled on the rotor 32.

In the present embodiment, the number of the concave grooves 331 on the driving wheel 33 is three, and the three concave grooves 331 are uniformly arranged on the outer circumferential surface of the connecting convex plate 332. Correspondingly, the rotor 32 is provided with three protrusions 321 at the bottom of the ring groove 322. It should be noted that the number of the grooves 331 on the driving wheel 33 is not limited to that shown in the drawings, and those skilled in the art can set the number of the grooves 331 on the driving wheel 33 to one, two, four, or even more according to the use requirement, and the positions of the grooves 331 on the outer circumferential surface of the connecting convex plate 332 can be arbitrarily set according to the use requirement, which will not be described herein.

In the present embodiment, the four-way valve of the present embodiment further includes a valve cover 40, the valve cover 40 is disposed on the valve body 10, and the valve cover 40 cooperates with the valve body 10 to form a gear housing for accommodating the gear assembly 35. The parts of the driving wheel 33 and the driven wheel 34 which are respectively meshed with the gear transmission assembly 35 are arranged in the gear box body, so that the gear meshing among the driving wheel 33, the gear transmission assembly 35 and the driven wheel 34 is protected, and the invasion of external impurities is prevented.

A bearing 41 is arranged between the driving wheel 33 and the valve cover 40 in the embodiment, so that the driving wheel 33 is rotatably connected with the valve cover 40, and the bearing 41 is arranged in the valve cover 40 and sleeved on the driving wheel 33, so that the driving wheel 33 can be radially limited.

To sum up, the utility model provides a cross valve, the rotation driving part on the available case realizes case location from top to bottom in the valve body with the assembly of rotation support portion to this saves the direction matching between case and the valve body, and the fit-up gap between case and the valve body on the multiplicable this cross valve, and fit-up gap between case and the valve body is big, prevent that the case from taking place wearing and tearing when the valve body internal rotation and between the valve body, can prevent to cause the dead situation of card to take place because of the entering of impurity between case and the valve body, have the effect that improves this cross valve job stabilization nature.

The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.

The above-mentioned embodiments only represent some embodiments of the present invention, and the description thereof is specific and detailed, but not to be construed as limiting the scope of the present invention. It should be noted that, for those skilled in the art, without departing from the spirit of the present invention, several variations and modifications can be made, which are within the scope of the present invention. Therefore, the protection scope of the present invention should be subject to the appended claims.

Claims

1. A four-way valve comprises a valve body with four valve ports, a valve core which is rotatably arranged in the valve body, and a driving mechanism; the driving mechanism can drive the valve core to rotate in the valve body; the method is characterized in that: one end of the valve core is provided with a rotary driving part, the other end of the valve core is provided with a rotary supporting part, the valve core is rotatably arranged on the valve body through the rotary supporting part, and a rotating shaft part of the driving mechanism is matched with the rotary driving part of the valve core and is used for driving the valve core to rotate in the valve body; the valve core is provided with a first flow channel and a second flow channel, the first flow channel is communicated with two of the valve ports on the valve body and forms a high-pressure cavity of the four-way valve, the second flow channel is communicated with the other two valve ports on the valve body and forms a low-pressure cavity of the four-way valve, a gap is reserved between the valve core and the valve body, and when the gap distance between the valve core at the high-pressure cavity side and the valve body is the largest, the gap distance between the valve core at the low-pressure cavity side and the valve body is the smallest.

2. The four-way valve of claim 1, wherein: the circle center line of the rotary driving part and the circle center line of the rotary supporting part are arranged on the same straight line.

3. The four-way valve of claim 1, wherein: the end face of the valve core, which is provided with the rotary driving part, is designed to be a planar structure.

4. The four-way valve of claim 3, wherein: the rotary driving part is a connecting boss, and the rotating shaft part of the driving mechanism is inserted into the connecting boss and matched with the key groove of the connecting boss.

5. The four-way valve of claim 4, wherein: the connecting boss is provided with a connecting groove which is matched with the upper rotating shaft part of the driving mechanism and extends to the inside of the valve core.

6. The four-way valve of claim 3, wherein: the valve core is provided with a limiting arc groove on the end face provided with the rotary driving part, the driving mechanism is provided with a limiting shaft, the limiting shaft is partially inserted into the limiting arc groove of the valve core, and the driving mechanism limits the rotary driving of the valve core through the matching between the limiting shaft and the limiting arc groove.

7. The four-way valve of claim 1, wherein: the valve body is provided with a supporting matching part, and the valve core is rotatably connected with the valve body through the matching between the rotating supporting part and the supporting matching part.

8. The four-way valve of claim 7, wherein: the rotary supporting part is provided with a round hole formed in the valve core, and the circle center line of the round hole and the circle center line of the valve core are arranged on the same straight line; the supporting matching part is a supporting convex column on the valve body, and the supporting convex column upwards extends into the round hole of the valve core.

9. The four-way valve of claim 8, wherein: the end face of the valve core, which is provided with the rotary supporting part, is designed to be a planar structure.

10. The four-way valve of claim 1, wherein: and a sealing pad bracket is fixed on the valve body, and a rotating shaft part of the driving mechanism penetrates through the sealing pad bracket and is matched with a key groove of a rotary driving part of the valve core.