Created on:2022-02-19 09:54

Introduction to check valve

Introduction to check valve

There are two kinds of check valves: ordinary check valve and hydraulic control check valve.

1. Ordinary check valve

Ordinary one-way valve, referred to as one-way valve, is a valve that only allows the forward flow of oil and does not allow the reverse flow. According to the different flow direction of oil in and out, it is divided into two structures: straight through type R (see Fig. 5 (a)] and right angle type [see Fig. 5 (b)]. It is composed of valve body, valve core and spring. When the liquid flows in from the oil inlet B, the oil pressure overcomes the spring resistance and the friction between the valve body 1 and the valve core 2, pushes open the valve core with conical end (steel ball can also be used as the valve core in order to simplify manufacturing when the flow is small) and flows out of the oil outlet P2. When the liquid flow reversely flows from P2, the oil pressure makes the valve core tightly press on the valve seat, so it cannot flow reversely. Figure 5 (c) shows the symbol of the check valve.

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The opening pressure of the check valve refers to the pressure difference between inlet P1 and outlet P2 when conducting in the positive direction. In order to make the one-way valve sensitive and reliable, with small pressure loss and reliable sealing performance, the opening pressure should be appropriate, generally about 0.04MPa. When the one-way valve is used as the back pressure valve, the spring with large stiffness shall be replaced to make it open in the positive direction. When it is connected, the opening pressure is large, resulting in a certain back pressure. Generally, the back pressure is 0.2 ~ 0.6MPa. The technical parameters of check valve products are shown in the table below.

Technical parameters of check valve products

model

通径(mm)

压力(MPa)

流量(L/min)

生产单位

DF

DIF

10 20 32

50 80

2131.5

251200

油研

S

6 8 10 15

20 25 30

31.5

10260

力士乐

 

2. Hydraulic control check valve

Figure 6 shows. It can be seen from the figure that the hydraulic control check valve has one more control oil port K, control piston L and ejector rod 2 than the ordinary check valve in structure.

When there is no pressure oil at the control oil port K, the hydraulic control check valve works the same as the ordinary check valve, that is, when the pressure oil enters from port P1, it can flow out from port P2. On the contrary, when the pressure oil enters from port P2, it cannot flow out from port P1. When the control port K is filled with pressure oil, the left side of the control piston 1 is under pressure, the right a cavity is connected with the oil drain port (not shown in the figure), the piston moves to the right, and the valve core 3 is pushed open through the ejector rod 2, so that the oil port P2 is connected with P1, and the oil flow direction can be changed freely. It can be seen that the hydraulic control check valve has one more function than the ordinary check valve, that is, reverse controllable opening. The graphical symbols of hydraulic control check valve are shown in Figure 6 (b).

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Figure 7 shows the hydraulic control check valve with unloading valve core. The connection mode of Figure 7 (a) is flange type, and the connection mode of Figure 7 (b) is plate type with electromagnetic pilot valve.

Take Fig. 7 (a) as an example to illustrate its working principle. The upper and lower ends of its main valve core (cone valve) 2 are provided with an axial small hole and four radial holes, and the axial small hole is closed by a small unloading valve core (cone valve) 3. When the high-pressure oil in chamber B needs to flow into chamber a in reverse (generally the working condition after the pressure maintaining of the hydraulic cylinder), and the control pressure oil pushes the control piston 6 upward, the control piston first pushes the unloading valve core upward for a small distance, so that the high-pressure oil in chamber B immediately flows out through the radial small hole of the valve core and the annular gap between the axial small hole and the lower end of the unloading valve core, The oil pressure in chamber B is reduced to realize pressure relief; Then, the main valve core is pushed open by the control piston to make the reverse oil pass smoothly. Due to the small control area of the unloading valve core, the unloading valve core can be pushed open with only a small force, which greatly reduces the control pressure required for reverse opening. The control pressure is only 5% of the working pressure, while the control pressure of the hydraulic control one-way valve without unloading valve core is as high as 40% ~ 50% of the working pressure of T. therefore, the hydraulic control one-way valve with unloading valve core is especially suitable for high-pressure and large flow hydraulic system.

The electromagnetic pilot valve 8 in Figure 7 (b) is fixed on the lower cover 7 of the one-way seal to control the on-off control of the pressure oil, which can simplify the oil circuit system and make the hydraulic system compact.

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Dual hydraulic control one-way valve fork weighs two-way hydraulic lock. Fig. 8 shows its structural schematic diagram. Two hydraulic control check valves with the same structure share a valve body, and four oil holes a, A1, B and B1 are opened on valve body 7. When the fluid flow of an oil circuit of the hydraulic system enters the valve in the forward direction from chamber a, the fluid flow pressure will automatically open the left valve core 2 to communicate between chamber a and A1, and the oil flows in the forward direction from chamber a to chamber A1. At the same time, the fluid flow pressure pushes the control piston 3 in the middle to the right, so as to push open the right valve core 4, communicate between chamber B and chamber B1, and discharge the oil originally closed on the passage of chamber B through chamber B. On the contrary, when the fluid flow of an oil circuit of the hydraulic system enters the valve from chamber B in the forward direction, the fluid flow pressure will automatically push open the right valve core 4, so that chamber B communicates with chamber B1, and the oil flows in the forward direction from chamber B to chamber B1. At the same time, the fluid flow pressure pushes the control piston 3 in the middle to the left, so as to push open the left valve core 2, make chamber a communicate with A1, and discharge the oil originally closed on the passage of chamber a through chamber a. To sum up, the working principle of the double hydraulic control check valve is that when one oil chamber enters the oil in the forward direction, the other oil chamber outputs the oil in the reverse direction, and vice versa. When there is no fluid flow in chamber a and chamber B, the reverse oil in chamber A1 and chamber B1 is closed under the tight contact between the conical surface of the valve core and the valve seat (hydraulic lock). Figure 9 shows the symbol of double hydraulic control check valve.

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The technical parameters of hydraulic control check valve are shown in the table below.

Technical parameters of hydraulic control check valve

型号

通径(mm)

压力(MPa)

流量(L/min)

生产单位

DFY

10 20 32

50 80

21

251200

油研

SV/SL

10 15 20

25 30

31.5

80400

力士乐

 

 

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