CN102242821B - High-low pressure switching valve for polyurethane high-pressure foaming machine - Google Patents

Abstract

The invention relates to the technical field of high-low pressure switching valves, in particular to a high-low pressure switching valve for a polyurethane high-pressure foaming machine. The invention comprises a valve body, wherein the valve body is provided with a feeding interface, a return interface, a first mixing head interface and a second mixing head interface which are respectively connected with a feeding hole of a mixing head through a pipe, a first high-pressure loop is formed between the feeding interface and the first mixing head interface, a second high-pressure loop is formed between the feeding interface and the second mixing head interface, a low-pressure unloading loop is formed between the feeding interface and the return interface, the valve body is provided with a low-pressure unloading valve core which can do linear reciprocating motion and control the low-pressure unloading loop to open and close, and the valve body is also provided with a high-pressure switching valve core which can do linear reciprocating motion and selectively control the first high-pressure loop and the second high-pressure loop to open and close. The invention can replace two sets of independent high-low pressure switching valves and one set of reversing valve, has convenient control and compact structure and can effectively reduce the number of the tubing.

Description

A high and low pressure switching valve for polyurethane high pressure foaming machine

technical field

The invention relates to the technical field of high and low pressure switching valves, in particular to a high and low pressure switching valve for polyurethane high pressure foaming machines.

Background technique

With the continuous improvement of the molding technology level and the improvement of the production process, the polyurethane foam industry has entered a new stage of development, and new technologies and new products are constantly emerging. In the actual production and processing process, polyurethane foam products (such as car seat cushions, car backrests, etc.) are mainly prepared by combining a polyurethane high-pressure foaming machine with a molding die.

In the process of preparing polyurethane foam plastic products by using a polyurethane high-pressure foaming machine, the raw materials (isocyanate or polyol) after heat treatment in the material tank enter the feeding channel of the mixing head through the metering pump and the high and low pressure switching valve in sequence; among them, There are two states in the mixing head, namely working state and standby state. When the mixing head is in the working state, the high-pressure circuit of the high-low pressure switching valve is opened, and the low-pressure unloading circuit is closed. At this time, all the raw materials entering the high-low pressure switching valve from the feeding interface enter the mixing head; when the mixing head is in standby state, The low-pressure unloading circuit of the high-low pressure switch valve is opened. At this time, the mixing head does not work. The low-pressure unloading circuit unloads the pressure of the raw materials entering the high-low pressure switching valve and reduces the pressure of the raw materials entering the mixing head. Some of the raw materials are directly unloaded through low pressure. The return interface of the circuit returns to the material tank.

With the continuous improvement of manufacturers' requirements for the processing efficiency of polyurethane foam products, the existing polyurethane high-pressure foaming machines are often connected with two (or even more than two) mixing heads; when working, by switching different mixing heads To meet the needs of forming molds in different positions to form polyurethane foam products. In order to achieve the above effects, different mixing heads are often connected to high and low pressure switching valves independently, and each mixing head must also be connected to the switching valve to realize the switching of the working state. The above-mentioned high-pressure polyurethane foaming machine often has many defects, such as The increase in the number of piping increases the burden of installation and commissioning work; in addition, since the high and low pressure switching valves and reversing valves are independent of each other, it will cause inconvenient control and increase the failure rate of the system.

Contents of the invention

The object of the present invention is to provide a high-low pressure switching valve for polyurethane high-pressure foaming machine in view of the deficiencies in the prior art. The high-low pressure switching valve for polyurethane high-pressure foaming machine has compact structure, less piping quantity and convenient control .

In order to achieve the above object, the present invention is achieved through the following technical solutions.

A high-low pressure switching valve for a polyurethane high-pressure foaming machine, including a valve body, the valve body is provided with a material inlet port, a material return port, and a first mixing head port connected to the feeding port of the mixing head through pipes, respectively. The second mixing head interface, a first high-pressure circuit is formed between the feeding interface and the first mixing head interface, and a second high-pressure circuit is formed between the feeding interface and the second mixing head interface. A low-pressure unloading circuit is formed between them. The valve body is equipped with a low-pressure unloading spool that can move linearly and reciprocate and control the opening and closing of the low-pressure unloading circuit. The valve body is also equipped with a linear reciprocating motion that selectively controls the first high-pressure circuit and The high-pressure switching spool for opening and closing the second high-pressure circuit.

Wherein, the valve body includes an upper valve body, an intermediate valve body and a lower valve body arranged in sequence, the high-pressure switching valve core is installed on the upper valve body, and the low-pressure unloading valve core is installed on the lower valve body. The first mixing head interface and the second mixing head interface are arranged on the upper valve body, the feeding interface is arranged on the middle valve body, and the material return interface is arranged on the lower valve body.

Wherein, the upper valve body includes a first component block, a second component block, a third component block, a fourth component block and a fifth component block, which are arranged in sequence and respectively opened with sequentially connected through holes. A mixing head interface is located in the first component block, and the second mixing head interface is located in the fifth component block. The high-pressure switching valve core includes a first valve stem, a first valve head, and a first valve head that are integrally formed and arranged in sequence along the axial direction. The second valve stem, the first valve stem, the first valve head and the second valve stem are sequentially nested in the through holes of the second component block, the third component block and the fourth component block, and the second component block is adjacent to the One side of the middle valve body is provided with a left feeding port, and the fourth component block is provided with a right feeding port at a side close to the middle valve body.

Wherein, the third component block is provided with a left oil inlet and outlet and a right oil inlet and outlet respectively connected with the through holes of the third component block, and the left oil inlet and the right oil inlet and outlet are respectively located on the left side of the first valve head and the right side.

Wherein, the two ends of the through hole of the third component block are respectively nested with first stoppers, and the first stoppers are clamped between the third component block and the second component block and between the third component block and the said second component block. Between the fourth component blocks, the first block is socketed with the corresponding first valve stem and the second valve stem.

Wherein, the middle valve body is provided with a left discharge port communicated with the left feed port and a right discharge port communicated with the right feed port, and the middle valve body is located on a side close to the lower valve body. A lower material outlet is provided, and the left material outlet, the right material outlet and the lower material outlet are respectively communicated with the material inlet interface.

Wherein, the lower valve body includes the sixth component block and the seventh component block respectively opened with through holes and the eighth component block opened with blind holes, the return interface is located in the seventh component block, and the low pressure unloading The valve core includes a second valve head and a third valve stem integrally formed, the second valve head is nested in the blind hole of the eighth component block, and the third valve stem is aligned with the lower outlet.

Wherein, the eighth component block is provided with upper oil inlet and outlet and lower oil inlet and outlet respectively connected with the internal blind hole, and the upper oil inlet and lower oil inlet and outlet are respectively located on the upper side and the lower side of the second valve head. side.

Wherein, the opening of the blind hole of the eighth component block is nested with a second stopper, the second stopper is clamped between the sixth component block and the eighth component block, and the second stopper is connected to the third component block. Stem socket.

Wherein, the seventh component block is provided with a mixing head return pipe interface that communicates with the discharge channel of the mixing head through piping, and the mixing head return pipe interface communicates with the through hole of the seventh component block.

The beneficial effects of the present invention are: a high-low pressure switching valve for polyurethane high-pressure foaming machines according to the present invention includes a valve body, the valve body is provided with a material inlet interface, a material return interface, and a pipe and a mixing head respectively. The first mixing head interface and the second mixing head interface connected to the feed port, the first high pressure circuit is formed between the feeding interface and the first mixing head interface, and the second mixing head interface is formed between the feeding interface and the second mixing head interface Two high-pressure circuits, a low-pressure unloading circuit is formed between the feeding interface and the returning material interface. The valve body is equipped with a low-pressure unloading valve core that can reciprocate in a straight line and control the opening and closing of the low-pressure unloading circuit. A high-pressure switching spool that reciprocates and selectively controls the opening and closing of the first high-pressure circuit and the second high-pressure circuit. The present invention connects two different mixing heads through the first mixing head interface and the second mixing head interface. When working, the present invention selectively controls the first high-pressure circuit and the second high-pressure circuit by controlling the position of the high-pressure switching spool. In addition, the present invention also switches the working state and standby state of the first high-pressure circuit or the second high-pressure circuit by controlling the position of the low-pressure unloading spool. The invention can effectively replace two sets of independent high and low pressure switching valves and one set of reversing valves, has convenient control, compact structure and can effectively reduce the number of pipes.

Description of drawings

The present invention will be further described below using the accompanying drawings, but the embodiments in the accompanying drawings do not constitute any limitation to the present invention.

Fig. 1 is a structural schematic diagram of the present invention.

Fig. 2 is a schematic cross-sectional view of the second mixing head interface of the present invention when it is in a working state.

3 is a schematic cross-sectional view of the second mixing head interface of the present invention when it is in a standby state.

Fig. 4 is a schematic cross-sectional view of the first mixing head interface of the present invention when it is in a working state.

Fig. 5 is a schematic cross-sectional view of the first mixing head interface of the present invention when it is in a standby state.

In Figures 1 to 5 include:

1——valve body 101——feed interface 102——return interface

103——The first mixing head interface 104——The second mixing head interface

11——The upper valve body 111——The first block

112——the second component block 112a——left feed port

113—the third block 113a—left oil inlet and outlet 113b—right oil inlet and outlet

113c——the first block 114——the fourth block 114a——the right feed port

115——Fifth component block 12——Middle valve body 121——Left material outlet

122——right outlet 123——bottom outlet 13——lower valve body

131 - the sixth component block 132 - the seventh component block 133 - the eighth component block

133a——upper oil inlet and outlet 133b——lower oil inlet and outlet 133c——second block

2——First high pressure circuit 3——Second high pressure circuit 4——Low pressure unloading circuit

5——low pressure unloading spool 51——second valve head 52——third valve stem

6——High pressure switching spool 61——First valve stem 62——First valve head

63——The second valve stem 7——The interface of the return pipe of the mixing head .

Detailed ways

It should be noted that the words "front", "rear", "left", "right", "upper" and "lower" used in the following descriptions all refer to the directions in the drawings, but the above words do not The specific assembly conditions and usage states of the present invention are limited.

The present invention will be further described below in conjunction with embodiment.

Embodiment 1, as shown in Figures 1 to 5, a high-low pressure switching valve for a polyurethane high-pressure foaming machine includes a valve body 1, and the valve body 1 is provided with a feeding interface 101, a feeding interface 102 and respective The first mixing head interface 103 and the second mixing head interface 104 that are connected to the feeding port of the mixing head through piping, the first high pressure circuit 2 is formed between the feeding interface 101 and the first mixing head interface 103, and the feeding interface 101 A second high-pressure circuit 3 is formed between the second mixing head interface 104, a low-pressure unloading circuit 4 is formed between the feeding interface 101 and the return interface 102, and the valve body 1 is equipped with a linear reciprocating motion and controls the low-pressure unloading circuit. 4 open and close low-pressure unloading spool 5, valve body 1 is also equipped with a high-pressure switching spool 6 that can linearly reciprocate and selectively control the opening and closing of the first high-pressure circuit 2 and the second high-pressure circuit 3.

The present invention is used to connect two different mixing heads, wherein, the first mixing head interface 103 and the second mixing head interface 104 are respectively independently connected to different mixing heads; Two high-pressure circuits that meet the working requirements of the two mixing heads, that is, the first high-pressure circuit 2 and the second high-pressure circuit 3, wherein the first high-pressure circuit 2 communicates with the first mixing head interface 103 and the feeding interface 101, and the second high-pressure circuit The circuit 3 communicates with the second mixing head interface 104 and the material feeding interface 101 . During work, the present invention selectively controls the opening and closing of the first high-pressure circuit 2 and the second high-pressure circuit 3 through the high-pressure switching spool 6, wherein, it must be further explained, the selective control can be understood as: when the polyurethane high pressure occurs When the bubble machine needs to fill the molding mold through the mixing head connected to the first mixing head interface 103, the high-pressure switching valve core 6 moves to the side of the second mixing head interface 104 and closes the second high-pressure circuit 3, and the first high-pressure Circuit 2 is opened, at this time, the raw material (isocyanate or polyol) after the heat treatment of the tank enters the mixing head through the first high-pressure circuit 2; similarly, when the polyurethane high-pressure foaming machine must When the connected mixing head performs filling processing on the forming mold, the high-pressure switching valve core 6 moves to the side of the first mixing head interface 103 and closes the first high-pressure circuit 2, and the second high-pressure circuit 3 is opened. At this time, the material tank is heated The processed raw material enters the mixing head through the second high-pressure circuit 3 .

In order to meet the requirements of being able to switch between the working state and the standby state of the first high-pressure circuit 2 or the second high-pressure circuit 3, the present invention is equipped with a low-pressure unloading spool 5 and a low-pressure unloading spool controlled by the low-pressure unloading spool 5 to open and close. Loop 4. Now take the mixing head connected to the first mixing head interface 103 as an example to illustrate the working condition of the low-pressure unloading spool 5: the first high-pressure circuit 2 is in the open state, when the mixing head is in the working state, the low-pressure unloading spool 5 will The low-pressure unloading circuit 4 is closed, and all the raw materials entering the valve body 1 from the feeding interface 101 enter the mixing head through the first high-pressure circuit 2; The low-pressure unloading circuit 4 opens the low-pressure unloading circuit 4. At this time, the low-pressure unloading circuit 4 unloads the pressure of the raw materials entering the valve body 1 and reduces the pressure of the raw materials entering the mixing head. Among them, a part of the raw materials directly pass through the low-pressure unloading circuit 4. The material return interface 102 returns to the material tank. Based on the above situation, it can be seen that the present invention controls three circuits (first high pressure circuit 2, second high pressure circuit 3 and low pressure unloading circuit 4) through two internal spools (low pressure unloading spool 5 and high pressure switching spool 6). Working conditions; therefore, the present invention can effectively replace two sets of independent high and low pressure switching valves and a set of reversing valves, with convenient control, compact structure and can effectively reduce the number of piping.

Further, the valve body 1 includes an upper valve body 11 , a middle valve body 12 and a lower valve body 13 arranged in sequence. Wherein, the upper valve body 11 includes a first component block 111 , a second component block 112 , a third component block 113 , a fourth component block 114 and a fifth component block 115 which are arranged in sequence and respectively opened with sequentially connected through holes. , the first mixing head interface 103 is located in the first component block 111, the second mixing head interface 104 is located in the fifth component block 115, and the high-pressure switching valve core 6 includes a first valve stem 61, a second A valve head 62 and a second valve stem 63, the first valve stem 61, the first valve head 62 and the second valve stem 63 are sequentially nested in the second component block 112, the third component block 113 and the fourth component block 114 In the through hole, the second component block 112 has a left feed port 112a on the side close to the middle valve body 12, and the fourth component block 114 has a right feed port 114a on the side close to the middle valve body 12; the middle valve The body 12 is provided with a left discharge port 121 communicated with the left feed port 112a and a right discharge port 122 communicated with the right feed port 114a, and the middle valve body 12 is provided with a lower discharge port near the lower valve body 13 The port 123, the left discharge port 121, the right discharge port 122 and the lower discharge port 123 are respectively communicated with the feed interface 101; 132 and the eighth block 133 with a blind hole, the return interface 102 is located at the seventh block 132, the low-pressure unloading valve core 5 includes a second valve head 51 and a third valve stem 52 integrally formed, the second valve head 51 is nested in the blind hole of the eighth component block 133 , and the third valve stem 52 is aligned with the lower outlet 123 .

The working process of the present invention will be further described below in conjunction with the specific structure of the above-mentioned valve body 1: the first mixing head interface 103, the left material inlet 112a, the left material outlet 121 and the material inlet 101 are connected in sequence and form the first high-pressure circuit 2. The second mixing head interface 104, the right inlet 114a, the right outlet 122, and the inlet interface 101 are connected in sequence to form the second high-pressure circuit 3, the inlet interface 101, the lower outlet 123, and the return interface 102 connected in sequence to form the low-pressure unloading circuit 4; when the first high-pressure circuit 2 is in working condition, the first valve stem 61 of the high-pressure switching spool 6 retreats from the first high-pressure circuit 2 and away from the first component block 111, and the high-pressure switching spool The top of the second valve stem 63 of 6 presses against the fifth component block 115 and closes the second high-pressure circuit 3. At this time, the low-pressure unloading valve core 5 moves up to the limit position and blocks the lower outlet 123, and the low-pressure unloading circuit 4 is closed. , at this time, the raw material after the heat treatment of the material tank enters the mixing head through the first high-pressure circuit 2; when the first high-pressure circuit 2 is in the standby state, the upper valve body 11 and the middle valve body 12 respectively maintain the The position when it is in the working state, that is, the first high-pressure circuit 2 is still open, the second high-pressure circuit 3 is still closed, the low-pressure unloading valve core 5 moves down to the limit position, the lower outlet 123 is turned on, and the low-pressure unloading circuit 4 is opened. At this time, a part of the raw material entering the intermediate valve body 12 from the feeding interface 101 flows back to the material tank through the return interface 102 of the low-pressure unloading circuit 4, and the other part still enters the mixing head through the first high-pressure circuit 2. The role of the low-pressure unloading circuit 4 The purpose is to unload the pressure of the raw material entering the intermediate valve body 12 and reduce the pressure entering the mixing head.

When the second high-pressure circuit 3 is in working condition, the second valve stem 63 of the high-pressure switching spool 6 withdraws from the second high-pressure circuit 3 and away from the fifth block 115, and the top end of the first valve stem 61 of the high-pressure switching spool 6 Press the first component block 111 and close the first high-pressure circuit 2, the low-pressure unloading valve core 5 moves up to the limit position and blocks the lower discharge port 123, the low-pressure unloading circuit 4 is closed, and the raw materials after the heat treatment of the material tank pass through the second The high-pressure circuit 3 enters the mixing head; when the second high-pressure circuit 3 is in the standby state, the upper valve body 11 and the middle valve body 12 maintain the position when the second high-pressure circuit 3 is in the working state, that is, the second high-pressure circuit 3 is still open, The first high-pressure circuit 2 is still closed, the low-pressure unloading spool 5 moves down to the limit position, the lower outlet 123 is turned on, and the low-pressure unloading circuit 4 is opened. At this time, a part of the raw material entering the middle valve body 12 from the feeding interface 101 Through the return interface 102 of the low-pressure unloading circuit 4, it flows back to the material tank, and the other part still enters the mixing head through the second high-pressure circuit 3.

As a preferred embodiment, the present invention controls the action of the high-pressure switching spool 6 and the low-pressure unloading spool 5 through hydraulic drive. In order to realize the above-mentioned control mode, the present invention adopts the following technical scheme: The left oil inlet and outlet 113a and the right oil inlet and outlet 113b respectively communicate with the through holes of the third component block 113, and the left oil inlet and outlet 113a and the right oil inlet and outlet 113b are respectively located on the left side and the right side of the first valve head 62; the eighth The component block 133 is provided with an upper oil inlet and outlet 133a and a lower oil inlet and outlet 133b respectively communicating with the internal blind hole. In the process of assembling the present invention on the polyurethane high-pressure foaming machine, the left oil inlet and outlet 113a, the right oil inlet and outlet 113b, the upper oil inlet and outlet 133a and the lower oil inlet and outlet 133b are respectively connected to the hydraulic pump of the hydraulic station through the oil pipeline, The first valve head 62 divides the through hole of the third component block 113 into a left cavity and a right cavity for hydraulic oil, and the second valve head 51 divides the blind hole of the eighth component block 133 into an upper cavity As well as the lower side cavity, the action process of the high-pressure switching spool 6 and the low-pressure unloading spool 5 is further described: when the hydraulic pump drives hydraulic oil into the left cavity of the third component block 113 from the left inlet and outlet port 113a, The high-pressure switching spool 6 moves toward the fifth block 115 under the action of the hydraulic oil and closes the second high-pressure circuit 3. At this time, the hydraulic oil previously retained in the right chamber of the third block 113 enters and exits the oil through the right The port 113b returns to the hydraulic station; when the hydraulic pump drives the hydraulic oil from the right inlet and outlet port 113b into the right chamber of the third block 113, the high-pressure switching spool 6 moves toward the first block 111 under the push of the hydraulic oil And the first high-pressure circuit 2 is closed. At this time, the hydraulic oil that previously stayed in the left chamber of the third component block 113 flows back to the hydraulic station through the left oil inlet and outlet port 113a; when the hydraulic pump drives the hydraulic oil from the upper inlet and outlet oil port 133a When entering the upper cavity of the eighth component block 133, the low-pressure unloading spool 5 moves toward the bottom end of the blind hole of the eighth component block 133 under the push of the hydraulic oil, and the low-pressure unloading circuit 4 opens. The hydraulic oil in the lower chamber of the eighth component block 133 flows back to the hydraulic station through the lower inlet and outlet port 133b; when the hydraulic pump drives the hydraulic oil into the lower chamber of the eighth component block 133 through the lower inlet and outlet port 133b, the low-pressure unloading valve The core 5 moves toward the opening side of the blind hole under the push of the hydraulic oil and closes the low-pressure unloading circuit 4. At this time, the hydraulic oil previously retained in the upper cavity of the eighth component block 133 flows back to the hydraulic station.

Further, both ends of the through hole of the third component block 113 are respectively nested with first stoppers 113c, and the first stoppers 113c are clamped on the third component block 113, the second component block 112 and the third component block 113. Between the block 113 and the fourth component block 114, the first block 113c is socketed with the corresponding first valve stem 61 and the second valve stem 63; similarly, at the opening of the blind hole of the eighth component block 133 A second stopper 133c is nested, and the second stopper 133c is clamped between the sixth component block 131 and the eighth component block 133 , and the second stopper 133c is socketed with the third valve stem 52 . The present invention seals the through hole of the third component block 113 through the first block 113c, wherein the first block 113c is respectively socketed with the first valve stem 61 and the second valve stem 63 on the corresponding side, in order to further ensure the above-mentioned For the sealing effect of the left cavity and the right cavity, the present invention can also add a sealing rubber ring between the first block 113c and the third component block 113 . Similarly, the present invention seals the blind hole of the eighth component block 133 through the second stopper 133c, wherein the second stopper 133c is socketed with the third valve stem 52, in order to further ensure the sealing effect of the above-mentioned upper cavity, In the present invention, a sealing rubber ring can also be added between the second block 133c and the eighth block 133 .

Embodiment 2. The difference between this embodiment and Embodiment 1 is that: the seventh component block 132 is provided with a mixing head return pipe interface 7 connected to the discharge channel of the mixing head through piping, and the mixing head return pipe interface 7 is connected to the first mixing head. The through holes of the seven groups of blocks 132 are connected. The mixing head return pipe interface 7 of the present invention is connected with the discharge channel of the mixing head through piping. The raw material to the corresponding mixing head directly flows into the mixing head return pipe interface 7 through the discharge channel of the mixing head and returns to the material tank through the return interface 102; therefore, by opening the mixing head return pipe interface at the seventh component block 132 7. The present invention can reduce the length and quantity of piping.

The above content is only a preferred embodiment of the present invention. For those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation and application scope. limits.

Claims (6)

1. A high-low pressure switching valve for polyurethane high-pressure foaming machines, including a valve body (1), characterized in that: the valve body (1) is provided with a material inlet port (101), a material return port (102) and The first mixing head interface (103) and the second mixing head interface (104) are respectively connected to the feed port of the mixing head through piping, and a second mixing head interface (103) is formed between the feeding interface (101) and the first mixing head interface (103). A high-pressure circuit (2), a second high-pressure circuit (3) is formed between the feed port (101) and the second mixing head port (104), and a second high-pressure circuit (3) is formed between the feed port (101) and the return port (102) There is a low-pressure unloading circuit (4), and the valve body (1) is equipped with a low-pressure unloading spool (5) that can move in a straight line and control the opening and closing of the low-pressure unloading circuit (4). A high-pressure switching spool (6) that reciprocates in a straight line and selectively controls the opening and closing of the first high-pressure circuit (2) and the second high-pressure circuit (3); The valve body (1) includes an upper valve body (11), an intermediate valve body (12) and a lower valve body (13) arranged in sequence, and the high-pressure switching valve core (6) is installed on the upper valve body (11 ), the low-pressure unloading spool (5) is installed on the lower valve body (13), the first mixing head interface (103) and the second mixing head interface (104) are installed on the upper valve body (11) , the feeding interface (101) is set on the middle valve body (12), and the feeding interface (102) is set on the lower valve body (13); The upper valve body (11) includes a first component block (111), a second component block (112), a third component block (113), and a fourth component block (111), which are arranged in sequence and respectively opened with sequentially connected through holes. block (114) and the fifth component block (115), the first mixing head interface (103) is located in the first component block (111), and the second mixing head interface (104) is located in the fifth component block (115) , the high-pressure switching valve core (6) includes a first valve stem (61), a first valve head (62) and a second valve stem (63) that are integrally formed and arranged in sequence along the axial direction, the first valve stem ( 61), the first valve head (62) and the second valve stem (63) are sequentially nested in the through holes of the second component block (112), the third component block (113) and the fourth component block (114), The second component block (112) has a left feed port (112a) on the side close to the middle valve body (12), and the fourth component block (114) has a left feed port (112a) on the side close to the middle valve body (12). Right inlet (114a); The third component block (113) is provided with a left oil inlet and outlet (113a) and a right oil inlet and outlet (113b) respectively connected to the through holes of the third component (113), and a left oil inlet and outlet (113a) and a right inlet and outlet The oil ports (113b) are respectively located on the left side and the right side of the first valve head (62); The middle valve body (12) is provided with a left material outlet (121) communicated with the left material inlet (112a) and a right material outlet (122) communicated with the right material inlet (114a), The middle valve body (12) is provided with a lower discharge port (123), a left discharge port (121), a right discharge port (122) and a lower discharge port ( 123) communicate with the feeding ports (101) respectively. 2. A high-low pressure switching valve for polyurethane high-pressure foaming machines according to claim 1, characterized in that: the two ends of the through holes of the third component block (113) are respectively nested with first The stopper (113c), the two first stoppers (113c) are respectively clamped on the third component block (113) and the second component block (112) and the third component block (113) and the first component block (113) Between the four blocks (114), the two first stoppers (113c) are respectively socketed with the corresponding first valve stem (61) and the second valve stem (63). 3. A high-low pressure switching valve for polyurethane high-pressure foaming machines according to claim 1, characterized in that: the lower valve body (13) includes sixth component blocks (131 ), the seventh component block (132) and the eighth component block (133) with a blind hole, the return interface (102) is located in the seventh component block (132), and the low-pressure unloading spool (5) includes There are integrally formed second valve head (51) and third valve stem (52), the second valve head (51) is nested in the blind hole of the eighth component block (133), the third valve stem (52) and The lower outlet (123) is aligned and set. 4. A high-low pressure switching valve for polyurethane high-pressure foaming machines according to claim 3, characterized in that: the eighth component block (133) is provided with upper inlet and outlet oil valves respectively connected to the internal blind holes The port (133a) and the lower oil inlet and outlet port (133b), the upper oil inlet and outlet port (133a) and the lower oil inlet and outlet port (133b) are respectively located on the upper side and the lower side of the second valve head (51). 5. A high-low pressure switching valve for polyurethane high-pressure foaming machines according to claim 4, characterized in that: the opening of the blind hole of the eighth component block (133) is nested with a second stopper (133c), the second block (133c) is clamped between the sixth component block (131) and the eighth component block (133), the second block (133c) and the third valve stem (52) set catch. 6. A high-low pressure switching valve for polyurethane high-pressure foaming machines according to claim 3, characterized in that: the seventh component block (132) is provided with a discharge channel through the pipe and the mixing head The connected mixing head return pipe interface (7), the mixing head return pipe interface (7) communicates with the through hole of the seventh component block (132).

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