Control valve

Technical field

The present invention relates to a control valve for use in a heating, ventilation and air conditioning system, in

particular to a flow regulating valve (RV) and a pressure independent control valve (PICV) .

Background art

The flow rate of a conventional electric regulating valve is easily affected by fluctuation in system pressure; as a result, electric regulating valves have the drawbacks of instability in the delivery of heat (cold) , poor resistance to interference and low precision of regulation. A dynamic balancing electric regulating valve is a product in which a dynamic balancing function is integrated with an electric regulating function. A mechanical dynamic balancing electric regulating valve enables the regulating valve to automatically balance the effect of system pressure on flow rate during actual operation of the system, so that an outputted flow rate characteristic curve and an ideal flow rate characteristic curve are identical and constant, i.e. independent of

pressure .

Some existing PICVs essentially employ a non-balancing design, encounter significant resistance during operation, and require a high-power actuator in order to perform control. In some other existing PICVs, a flow rate presetting function is realized by means of valve stem limiting, hence the valve stem not only serves to guide, but also has a limiting action.

Furthermore, there is another existing PICV in which a valve stem is also used as a pressure-leading passage, because a flow-leading gap is small.

Content of the invention

In view of the above, a control valve is proposed in an embodiment of the present invention, for controlling a flow rate of a fluid in a fluid passage. The control valve can realize flow rate presetting in a rotational manner, with no need for a pressure-leading passage to be formed in the valve stem, hence the difficulty of machining the valve stem is reduced, and the stability of the valve stem is increased.

In an embodiment of the present invention, the control valve comprises: a valve body, having an internal cavity, the internal cavity having an inlet passage and an outlet passage; a first valve assembly, disposed between the inlet passage and the outlet passage, the first valve assembly comprising: a valve seat, being in the shape of a cylinder having an opening at one end, and being fixed relative to the valve body, wherein an opening extending in a circumferential direction is provided in a sidewall of the valve seat; a slider, disposed close to an outer wall of the valve seat, and being capable of moving in the circumferential direction of the outside wall of the valve seat in order to block a part or all of the opening, but being fixed in an axial direction of the valve seat; a regulating valve plug, being in the shape of a cylinder having openings at both ends, being nested concentrically in the valve seat and being capable of moving in the axial direction of the valve seat, in order to partially or completely block the opening in the axial direction of the valve seat, wherein the slider and the regulating valve plug are driven

independently. In a preferred embodiment, the opening provided in the sidewall of the valve seat extends in the

circumferential direction through about 170° - 190°.

It is envisaged that the slider is capable of moving in the circumferential direction of the outside wall of the valve seat in order to cover all of the opening.

It is also envisaged that the slider is capable of moving in the circumferential direction of the outside wall of the valve seat in order to cover a part of the opening.

It is also envisaged that the slider is capable of moving in the circumferential direction of the outside wall of the valve seat in order to cover a portion of the opening.

The control valve in this embodiment of the present invention is a mechanical dynamic balancing electric

regulating valve, and can automatically balance the effect of HVAC system pressure on flow rate. In an embodiment of the present invention, the first valve assembly contained in the control valve has a flow rate presetting function and a flow rate regulating function. The flow rate presetting function is realized by driving the slider to partially or completely block the opening in the sidewall of the valve seat in the circumferential direction. Throughout the process of flow rate regulation, the slider is stationary relative to the valve seat/valve body in the axial direction. Such a flow rate presetting function can be realized by rotary driving; this can control the flow rate with greater precision. The flow rate regulating function is realized by driving the regulating valve plug to partially or completely block the opening in the side of the valve seat in the axial direction, and can perform flow rate regulation within a preset flow rate range. Thus, flow rate presetting and flow rate regulation are driven independently of each other; hence, when the regulating valve plug is unable to move axially due to a fault, it is still possible for the effect on the system to be reduced by

regulating the preset flow rate. Furthermore, having the slider disposed on the outside of the valve seat simplifies the assembly complexity, and facilitates driving. In addition, in this embodiment, the regulating valve plug is a cylindrical hollow structure having openings at two ends, so fluid can pass therethrough. Thus, there is no pressure difference between the two ends of the regulating valve plug in the axial direction, i.e. the structure is balanced. The actuator driving force required by such a balanced structure is very small, so there is an obvious advantage over a non-balanced design .

In an embodiment, the slider comprises: a blocking sidewall extending in the circumferential direction of the outer wall of the valve seat; a shaft part extending in the axial

direction of the valve seat; and a connecting part connecting the blocking sidewall and the shaft part; wherein the shaft part projects from one end of the valve body in a rotatable manner, and the slider can rotate synchronously with the shaft part. Preferably, the control valve further comprises a drive disk, which is outside the valve body and provided in a sheathing manner on the projecting shaft part, and is capable of rotating synchronously with the shaft part. In this

embodiment, an operator can drive the slider to move in the circumferential direction of the outer wall of the valve seat by turning the drive disk, and can thereby realize flow rate presetting conveniently, without any other interfering

factors. More preferably, the slider is an integral member, with the rotatable shaft part and blocking sidewall thereof both being integrally formed, to facilitate both machining and operation .

In an embodiment, the control valve further comprises a valve stem, having one end projecting from one end of the valve body, and another end connected to the regulating valve plug, and capable of being driven to drive the regulating valve plug to move in the axial direction of the valve seat. Preferably, the valve stem is disposed in an axial position of the regulating valve plug, and is connected by means of at least two spokes to a sidewall of the regulating valve plug. Thus, flow rate regulation is achieved through axial movement of the valve stem, and flow rate presetting is achieved through rotation of the drive disk; the two functions do not interfere with one another, and are easy to realize. At the same time, there is no need to provide a pressure-leading passage in the valve stem, so the valve stem has a simple design, convenient installation and a long service life.

In an embodiment, the control valve further comprises a second valve assembly, disposed between the inlet passage and the outlet passage. The second valve assembly is separated in space from the first valve assembly, the second valve assembly being a balancing valve assembly, and being used to balance a pressure difference between an inlet and an outlet of the first valve assembly. Preferably, the second valve assembly is disposed downstream of the first valve assembly, and the second valve assembly is capable of regulating a flow rate according to the difference between a first fluid pressure at the inlet passage and a second fluid pressure between the first and second valve assemblies. Here, the second valve assembly is a pressure difference balancing valve. In an embodiment, the first valve assembly and the second valve assembly are preferably positioned one above the other, and the second valve assembly is located downstream of the first valve assembly. Here, since the first valve assembly and the second valve assembly are separated in space, the two valve assemblies do not interfere with one another, have stable operating states, and are easy to install, with a relatively simple structure.

In an embodiment, the second valve assembly preferably comprises: a movable balancing valve plug, being in the shape of a cylinder having an opening at one end, and being capable of displacement in an axial direction thereof so as to change a flow rate of flow to the outlet passage, wherein one side of the balancing valve plug is subjected to an applied force of the first fluid pressure at the inlet passage, another side is subjected to a resultant force of an applied force of an elastic member and an applied force of the second fluid pressure, and the balancing valve plug attains a balanced state under the joint action of the forces at the two sides.

In this embodiment, the second valve assembly can ensure that the difference between the first and second fluid

pressures is a constant value by regulating the flow rate.

When the control valve is affected by a change in HVAC system pressure, the second valve assembly can respond quickly, balancing the effect of system pressure on the valve, and reducing noise and system vibration. The abovementioned mechanical structure of the second valve assembly can also ensure that the control valve still has a dynamic balancing function in a state in which electricity is cut off.

In an embodiment, the second valve assembly specifically comprises: a rolling diaphragm in sealed connection with the valve body, one side of the rolling diaphragm being subjected to the applied force of the first fluid pressure, and another side abutting an outer wall of the balancing valve plug; the elastic member, disposed inside the balancing valve plug and being capable of extending and retracting in the axial

direction of the balancing valve plug, the elastic member having one end fixed and another end abutting an inner wall of the balancing valve plug. The rolling diaphragm in this embodiment can transmit the applied force of the first fluid pressure to the balancing valve plug. The rolling diaphragm has a small volume and is convenient to use; moreover, when the rolling diaphragm is used, almost no friction will arise, so delay errors in flow rate control can be reduced.

In an embodiment, the control valve further comprises a first pressure-leading tube, which is disposed on the valve body and used for establishing communication between the inlet passage and said one side of the rolling diaphragm. Compared with using a valve shaft directly as a pressure-leading passage, the provision of the first pressure-leading tube on the valve body gives a more reliable structure, which does not become blocked easily, and is easy to realize and maintain.

In an embodiment, the second valve assembly further comprises: a valve plug cover, being fixed to the valve seat in the axial direction, and covering the opening of the balancing valve plug in a radial direction, with at least one through-hole being provided in the valve plug cover, and the fluid in the fluid passage being capable of flowing through the through-hole into the interior of the balancing valve plug. The valve plug cover in this embodiment can increase the stability of water flow inside the balancing valve plug, thereby reducing turbulence inside the balancing valve plug, as well as vibration and noise caused by turbulence. In an embodiment of the present invention, a small through-hole is used to establish fluid communication between the inside and outside of the balancing valve plug; the small hole can prevent large impurities from entering the balancing valve plug .

In an embodiment, the second valve assembly and the first valve assembly are positioned one above the other, and the valve stem is disposed in such a way as to pass through the balancing valve plug and the valve plug cover, with the elastic member being provided on the valve stem in a sheathing manner, and having one end fixed to the valve plug cover. The valve stem also has a guiding action on the first valve assembly .

It is envisaged that the second valve assembly and the first valve assembly are positioned one above the other, and the valve stem is disposed in such a way as to pass through the balancing valve plug and the valve plug cover, with the elastic member being sleeved on the valve stem, and having one end fixed to the valve plug cover. The valve stem also has a guiding action on the first valve assembly.

It can be seen from the solution above that an embodiment of the present invention is a product in which dynamic

balancing and electric regulation are integrated. The use of a mechanical dynamic balancing electric regulating valve enables the system to automatically balance the effect of system pressure on flow rate during actual operation, so that an outputted flow rate characteristic curve and an ideal flow rate characteristic curve are identical and constant.

Description of the accompanying drawings

Preferred embodiments of the present invention are

described in detail below with reference to the accompanying drawings, to give those skilled in the art a clearer

understanding of the abovementioned and other features and advantages of the present invention. Drawings:

Fig. 1 is a three-dimensional view of a section in the Y direction of a control valve according to an embodiment of the present invention.

Fig. 2A is a view of a section in the Y direction of a first valve assembly 120 in the embodiment shown in Fig. 1.

Fig. 2B is an exploded view of the first valve assembly 120 in the embodiment shown in Fig. 1.

Fig. 3 is an enlarged drawing of a flow rate graduated disk in the embodiment shown in Fig. 1.

Fig. 4 is a view of a section in the Y direction of a second valve assembly 130 in the embodiment shown in Fig. 1.

Key to the drawings :

100: control 110: valve

valve ; body;

111: inlet 112: outlet 113: fluid

passage ; passage ; passage;

114 : first 119: fixing 118 :

pressure nut ; communication

leading tube ; port ;

120: first

valve

assembly;

121: valve 1212: opening; 1214 : sealing

seat ; ring;

123: slider; 1231 : blocking 1233: shaft 1235:

sidewall ; part ; connecting part ;

124 : 125: first

regulating valve stem;

valve plug;

130: second

valve

assembly;

131 : balancing 132: elastic 133: rolling 134 : valve valve plug; member; diaphragm; plug cover;

150 : drive 501 : valve

disk; seat opening.

Particular embodiments

In order to clarify the object, technical solution and advantages of the present invention, the present invention is explained in further detail below by way of embodiments.

Fig. 1 is a three-dimensional sectional view of a control valve 100 according to an embodiment of the present invention. As shown in Fig. 1, in an embodiment of the present invention, a valve body 110 of the control valve 100 (an actuating mechanism connected to the control valve 100 is not shown) is connected in a fluid passage, and used for controlling a flow rate of a fluid in the fluid passage. The valve body 110 has an internal cavity, through which the fluid flows. The fluid flowing through the internal cavity of the valve body 110 may be a liquid, such as water or a water-containing mixture, and may also be a gas, such as vapor. A communication port 118 is provided in the internal cavity of the valve body 110; the communication port divides the internal cavity into an inlet passage 111 and an outlet passage 112. Here, the concepts of inlet and outlet are relative, not restrictive. Depending on actual application needs, the fluid could also enter through the outlet passage 112 and flow out through the inlet passage.

As shown in Fig. 1, a first valve assembly 120 and a second valve assembly 130 are provided in the internal cavity of the valve body 110. The first valve assembly 120 is disposed below the communication port 118, can preset a flow rate through the internal cavity of the valve body 110, and can regulate the flow rate in response to actuator control within a range defined by the preset flow rate. The second valve assembly 130 is a pressure difference balancing valve, which can

automatically balance a pressure difference between an inlet and outlet of the first valve assembly 120 within a certain range, to ensure that the flow rate is independent of pressure. In the example of Fig. 1, a pressure at the inlet of the first valve assembly 120 is a pressure (PI) at the inlet passage 111, and a pressure at the outlet of the first valve assembly 120 is a pressure (P2) at the communication port 118.

In the example shown in Fig. 1, the first valve assembly 120 and the second valve assembly 130 are separated from each other in space. Within the internal cavity, the first valve assembly 120 may be located upstream of the second valve assembly 130, or be located downstream of the second valve assembly 130. In the example shown in Fig. 1, the first valve assembly 120 and the second valve assembly 130 are positioned one above the other in a cavity body between the inlet passage and the outlet passage, and the first valve assembly 120 is located upstream of the second valve assembly 130. In other embodiments, the second valve assembly 130 could also be located upstream of the first valve assembly 120; the relative positions thereof are determined by the specific application circumstances. Of course, due to the change in position of the second valve assembly 130, an internal structure thereof would also be adjusted correspondingly; this point will be obvious to those skilled in the art.

Suppose that a fluid pressure at the inlet passage 111 is a first fluid pressure PI. Due to a regulating action of the first valve assembly 120, a fluid pressure at a fluid passage 113 between the first valve assembly 120 and the second valve assembly 130 is a second fluid pressure P2. There might be a pressure difference between the first fluid pressure PI and the second fluid pressure P2. A fluid pressure at the outlet passage 112 is a third fluid pressure P3. The second valve assembly 130 can regulate a degree of opening toward the outlet passage 112 according to the difference between the first fluid pressure PI and the second fluid pressure P2, and thereby ensure that the flow rate through the control valve 100 is independent of the pressure difference between the first fluid pressure PI at the inlet passage and the second fluid pressure P2 at the outlet passage.

If the flow direction of fluid shown in Fig. 1 is reversed, i.e. the fluid flows in through passage 112 (first fluid pressure PI) and flows out through passage 111 (third fluid pressure P3) , then the second valve assembly 130 is located upstream of the first valve assembly 120. At this time, the pressure difference between the inlet and outlet of the first valve assembly 120 is the pressure difference between P2 and P3, i.e. the second valve assembly 130 must balance the pressure difference between P2 and P3. In this situation, the specific structure of the second valve assembly 130 may be different from that shown in Fig. 1.

First valve assembly - flow regulating valve

Figs. 2A and 2B show a sectional drawing and an exploded drawing of the first valve assembly 120 in Fig. 1

respectively. In the embodiment shown in Figs. 2A and 2B, the first valve assembly 120 specifically comprises a valve seat 121, a slider 123 and a regulating valve plug 124. As shown in Fig. 2A, the valve seat 121 is disposed at the communication port 118 and fixed to the valve body 110, the regulating valve plug 124 is nested in the valve seat 121, and the slider 123 is preferably provided on the valve seat 121 in a sheathing manner and capable of sliding in the circumferential direction of the outer wall of the valve seat 121. The slider 123 and the regulating valve plug 124 can be driven independently of each other.

As shown in Fig. 2B, the valve seat 121 is substantially in the shape of a cylinder having an opening at one end (or is similar in shape to an inverted bell jar) . In Fig. 2B, an opening 501 of the valve seat 121 is located at an upper end face of the valve seat 121; the opening 501 is substantially equal in size to an internal diameter of the valve seat 121, and serves as a fluid outlet of the valve seat 121. The regulating valve plug 124 can be inserted into the valve seat 121 through the opening 501. A sidewall of the valve seat 121 is provided with an opening 1212 extending in the

circumferential direction thereof. The opening 1212 may for example extend through about 170° - 190° in the

circumferential direction of the valve seat. The size of the opening 1212 determines a maximum preset flow rate of the control valve 100. In other embodiments, the opening 1212 may also be designed to extend circumferentially through other angles, according to a maximum value of preset flow rate. It can be seen from Figs. 2A and 2B that in the absence of any blocking, fluid coming from the inlet passage 111 can flow into the valve seat 121 through the opening 1212 of the valve seat 121, and flow out through the opening 501.

As shown in Figs. 2A and 2B, the slider 123 is disposed at the outside wall of the valve seat 121, and is adapted to slide in the circumferential direction of the outside wall of the valve seat 121, in order to partially or completely block the opening 1212. Preferably, the slider 123 is disposed close to a part where the opening 1212 is located, i.e. a lower half of the valve seat 121 in the figures. More preferably, the slider 123 is provided in a sheathing manner at the part where the opening 1212 of the valve seat 121 is located.

More preferably, the slider 123 is driven by means of a turning operation. Specifically, as shown in Fig. 2B, the slider 123 comprises an arcuate blocking sidewall 1231, a shaft part 1233 extending along an axis of the valve seat, and a connecting part 1235 connecting the blocking sidewall 1231 and the shaft part 1233. Referring to Figs. 2A and 2B, the blocking sidewall 1231 of the slider 123 is an arcuate

blocking piece or blocking plate, with an internal diameter of the arcuate shape matching an external diameter of the valve seat 121. In the example shown in Fig. 2B, the blocking sidewall 1231 is preferably a cylinder wall extending

substantially through half a circumference (e.g. about 170 - 190 degrees), and can partially or completely block the opening 1212 in the valve seat 121 by sliding. A preset flow rate value is regulated by adjusting the size of the opening 1212 that is blocked by the slider 123 in the circumferential direction, to realize a flow rate presetting function. The shaft part 1233 can project from the bottom of the control valve, in order that an operator can perform a turning

operation on the shaft part. The connecting part 1235 may be a fan-shaped flat plate, separated from a hermetic end of the valve seat 121 by a predetermined gap, in order to rotate relative to the valve seat 121. By turning the shaft part 1233 projecting from the bottom of the control valve, it is

possible to change the size of the blocked part of the opening 1212, i.e. change the preset flow rate, without the slider 123 being displaced in an axial direction Z.

Fig. 3 shows a partial enlarged drawing of the bottom of a control valve according to an embodiment of the present invention. As shown in Fig. 3, preferably, a drive disk 150 may be provided in a sheathing manner on (or sleeved on) the shaft part 1233 of the slider 123. The drive disk 150 may drive the shaft part to turn synchronously, thereby causing the blocking sidewall 1231 to turn synchronously. Preferably, graduations are marked on the drive disk 150, to indicate the size of the preset flow rate. Correspondingly, a pointer mark 152 may be provided on the valve body of the control valve; the size of the current preset flow rate is shown by the graduation pointed to by the pointer mark.

In a preferred embodiment, the bottom of the valve body 110 has a hole; the shaft part 1233 is adapted to pass through the hole and the drive disk 150 in a rotatable fashion. A fixing nut 119 is adapted to be screwed onto the shaft part 1233, in order to fix the drive disk and the shaft part immovably relative to the valve body 110 in the axial direction. A sealing ring is also preferably provided in the hole in the bottom of the valve body 110, to prevent leakage.

Thus, employing the manner of assembly shown in Fig. 3, an operator can realize flow rate presetting by turning the drive disk 150, and obtain the current preset flow rate directly from the graduation reading. This manner of rotational setting is accomplished independently and can avoid unnecessary interference; moreover, the mating structure is simple, and easy to implement.

As shown in Figs. 2A and 2B, the regulating valve plug 124 is in the form of a cylinder having openings at both ends, is nested concentrically in the valve seat 121, and is in close contact with an inside wall of the valve seat 121 in such a way as to be capable of moving in the axial direction Z

(moving up and down in the figure) . Preferably, a sealing ring is provided at sidewalls, facing each other, of the valve seat 121 and the regulating valve plug 124, to prevent leakage. The movement of the regulating valve plug 124 in the axial

direction of the valve seat 121 can partially or completely block the opening 1212 in the valve seat 121 in the axial direction, thereby further regulating the flow rate within a preset flow rate range. Preferably, an overlap amount of the regulating valve plug 124 and the valve seat 121 in the axial direction can be changed by operating a valve stem 125

connected to the regulating valve plug 124. The valve stem 125 has one end connected to the regulating valve plug 124, and another end projects from the top of the valve body 110 and is then connected to an actuator (not shown) . The actuator can drive the valve stem 125 to move in the axial direction Z according to a control instruction, thereby changing the position of the regulating valve plug 124 relative to the valve seat 121 in the axial direction, i.e. changing the blocked amount of the opening 1212 in the axial direction. In the example shown in Fig. 2B, the valve stem 125 is disposed along the axis of the valve seat/regulating valve plug, and connected to the sidewall of the regulating valve plug 121 by means of at least two spokes.

More preferably, in the embodiment of Fig. 2B, the first valve assembly 120 also comprises multiple sealing rings, to prevent leakage. For example, the valve seat 121 is provided with a sealing ring 1214 at a part facing an end face of the regulating valve plug 124. As another example, a sealing ring 1214 is also provided between the valve seat 121 and the valve body 110.

Second valve assembly - pressure difference balancing valve

Fig. 4 shows an enlarged drawing of a sectional front view of the second valve assembly 130 in Fig. 1. The second valve assembly 130 is a pressure difference balancing valve

structure, i.e. the second valve assembly 130 can regulate the flow rate according to the difference between the first fluid pressure PI at the inlet passage 111 and the second fluid pressure P2 in the fluid passage 113, thereby controlling the flow rate through the control valve 100 and realizing pressure difference balancing.

Specifically, as shown in Fig. 4, the second valve assembly 130 comprises a movable balancing valve plug 131, which is in the shape of a cylinder having an opening at one end (or is similar in shape to a bell jar), and can be displaced in the axial direction Z thereof. In Fig. 3, the displacement of the balancing valve plug 131 along the Z axis changes the size of an opening between the balancing valve plug 131 and the valve seat 121, said opening being in communication with the outlet passage 112. Thus, the displacement of the balancing valve plug 131 can change the flow rate of fluid flowing toward the outlet passage 112.

In Fig. 4, the balancing valve plug 131 is located

downstream of the regulating valve plug 124, and in terms of spatial position is superposed above the regulating valve plug 124. The balancing valve plug 131 has a downward opening, and is in the shape of a bell jar. In other embodiments, in addition to a circular shape, a cross section of the movable balancing valve plug 131 could also be elliptical, square or another irregular shape, etc. An elastic member 132 is disposed inside the balancing valve plug 131; the elastic member 132 has one end fixed and another end abutting the bottom of an inner wall of the balancing valve plug 131. The interior of the balancing valve plug 131 is in fluid

communication with the first valve assembly 120, so that a fluid pressure borne by the inner wall of the balancing valve plug 131 is the second fluid pressure P2, and equal to the fluid pressure at the outlet 501 of the first valve assembly 120. As shown in Fig. 1, a pressure-leading tube 114 leads fluid from the inlet passage 111 to the top of an outer wall of the balancing valve plug 131, i.e. a top face of the balancing valve plug 131 is subjected to the same first fluid pressure PI as the inlet passage 111. Thus, inside the

balancing valve plug 131, an elastic force f applied by the elastic member 132 and a force applied by the second fluid pressure P2 (an upward resultant force FI in the figure) act together on the inside top of the balancing valve plug 131. At the same time, outside the balancing valve plug 131, the first fluid pressure PI identical to the pressure at the inlet passage 111 acts on the outside top of the balancing valve plug 131 (this force F2 is directed downward in the figure) . Under the joint action of the inside and outside pressures, the balancing valve plug 131 can attain a balanced state, i.e. FI = F2. If a change occurs in the first fluid pressure PI and/or the second fluid pressure P2, the balancing valve plug 131 is displaced because the forces at the two sides are not balanced (FI ¹ F2), until the inside and outside pressures attain a balanced state (FI = F2) again. Thus, an adjustable outlet flow rate of the pressure difference balancing valve is independent of the fluid pressures at the inlet passage and the outlet passage, and is only dependent on the pressure difference between PI and P2, i.e. a restoring force of the elastic member. Here, a maximum elastic restoring force of the elastic member is a preset value, which determines a maximum value of the difference between the first fluid pressure PI and the second fluid pressure P2. For control valves of different flow rate grades, the preset values of the maximum restoring force of the elastic member are different.

In the specific example shown in Figs. 1 and 4, the balancing valve plug 131 is movably disposed downstream of the first valve assembly 120. The balancing valve plug 131 can be inserted into the valve body from an upper part of the valve body 100, and the valve stem 125 is passed therethrough. The balancing valve plug 131 can be displaced in the axial

direction of the valve stem 125 (i.e. the Z direction) . Here, the elastic member 132 is disposed inside the balancing valve plug 131, and is similarly provided on the valve stem 125 in a sheathing manner, or sleeved on the valve stem 125. One end of the elastic member 132 abuts the inner wall (inside top) of the balancing valve plug 131; another end is fixed, e.g. fixed to the valve seat or fixed to a component of the valve seat. The extension/retraction of the elastic member 132 may be used to balance the difference between the fluid pressures PI and P2. Here, the elastic member 132 preferably may be a spring, e.g. a coil spring. In other embodiments, the elastic member 132 may also be selected from other flexible elements capable of storing energy. Here, the valve stem 125 also has a guiding action, and can cause the balancing valve plug 131 and the elastic member 132 to move in the direction in which the valve stem 125 lies, in order to avoid tilting, such that guiding and limiting functions are more reliable.

In the example in Figs. 1 and 4, the outer wall of the balancing valve plug 131 abuts a rolling diaphragm 133 made of a flexible material. An edge of the rolling diaphragm 133 is in sealed connection with the valve body 110/valve stem 135.

In actual applications, the rolling diaphragm 133 may be made of any suitable flexible material. The rolling diaphragm 133 may be made with O-shaped annular edges at the top and bottom, or with fixing holes at the periphery of the bottom, or in another form. In a specific embodiment, the rolling diaphragm 133 may be made of a rubber material such as nitrile butadiene rubber or epichlorohydrin rubber, and/or a polyester film and/or a metal foil, or another material. As shown in Fig. 4, a region above the rolling diaphragm 133 is in fluid

communication with the first pressure-leading tube 114, and is at a fluid pressure equal to PI. In other words, the rolling diaphragm 133 transmits the first fluid pressure PI borne thereby to the top face of the balancing valve plug 131. A region below the rolling diaphragm 133 is in communication with the outlet of the first valve assembly 120, and is at a fluid pressure equal to P2. Thus, the rolling diaphragm 133 can isolate the region at the first fluid pressure PI from the region at the second fluid pressure P2. In actual

applications, when the first fluid pressure PI increases, the balanced state that was originally attained is broken; the rolling diaphragm 133 pushes the balancing valve plug 131 to move downward, compressing the elastic member 132, until the balancing valve plug 131 attains a balanced state again, i.e. the resultant force of the elastic force f and the force applied by the second fluid pressure P2 to the inside top (inner wall) of the balancing valve plug 131 is substantially equal to the force applied by the first fluid pressure PI to the outside top (outer wall) of the balancing valve plug 131 via the rolling diaphragm. Thus, the balancing valve plug 131 can adjust a flow rate of a flow passage according to the difference between the first and second fluid pressures.

Preferably, an opening side (lower end) of the balancing valve plug 131 may also comprise a valve plug cover 134.

Preferably, the valve plug cover 134 is fixed to the valve seat 121 in the axial direction and is separated from the valve seat 121 by a predetermined distance, and covers the opening of the balancing valve plug 131 in a radial direction. The valve stem 125 similarly passes through the valve plug cover 134 in such a way as to be capable of relative movement. A through-hole is provided in the valve plug cover 134;

preferably, multiple through-holes are arranged uniformly in the valve plug cover, to enable fluid to flow into the

interior of the balancing valve plug 131. Another function of the valve cover 134 is to reduce turbulence and noise inside the balancing valve plug 131, and prevent foreign matter from flowing into the interior of the balancing valve plug.

The second valve assembly has been described above with reference to Figs. 1 and 4. As stated above, if the fluid direction shown in Fig. 1 changes, i.e. fluid flows in through passage 112 and flows out through passage 111, then the second valve assembly 130 needs to balance the pressure difference between P2 and P3; a corresponding structure may be different from that shown in Figs. 1 and 4. For example, the elastic member 132 in the second valve assembly 130 is at the same side as the rolling diaphragm, i.e. a force at one side of the balancing valve plug 131 comes from P2, and a force at another side is the resultant force of the fluid pressure P3 at an outlet and the elastic force applied by the elastic member.

In addition, as shown in Fig. 1, a valve cover is also provided at the top of the control valve 100, and removably fixed to the valve body 110. With the valve cover removed, the first and second valve assemblies can be conveniently inserted into the fluid passage from the top; moreover, an opening is provided in the valve cover, and the valve stem 125 can pass out through the opening and be connected to the actuator.

The embodiments above are merely preferred embodiments of the present invention, which are not intended to limit it. Any amendments, equivalent substitutions or improvements etc. made within the spirit and principles of the present invention shall be included in the scope of protection thereof.