One of the main characteristics of the excavator pressure transmission compared with other transmissions is the use of more types and numbers of valves to control the direction, flow and pressure of the liquid flow, so as to realize the action of hydraulic machinery under different operating conditions. Many, according to their role in the hydraulic system, can be divided into the following categories (see Table 1-2)
1. Pressure control valve
Used to control or adjust the hydraulic pressure valves in the hydraulic system, such as safety valves, overflow valves, back pressure valves, etc.
2. Flow control valve
Maintain the liquid flow at a certain value to adjust the movement speed of the working mechanism, such as throttle valve and stroke control
3. Direction control valve
is used to control the direction of liquid flow. There are two types of directional valve and one-way valve. The directional valve is divided into two types: spool valve and rotary valve.
Among hydraulic excavators, the most used is the directional valve (also known as the control valve). It is often used to directly control the movement direction of each working mechanism of the hydraulic digging machine. In order to reduce the installation volume of the directional valve and facilitate the connection of the oil circuit, it is often used to connect several directional valves and safety valves with bolts, or to form the valve body as a whole, called the multi-directional valve group, also known as Multi-way combination valve.
Valve type directional valve has good sealing and sensitive action, but the force required to open the valve is large, so it is rarely used.
Rotary valve type reversing valve relies on the spool to rotate in the valve body to change the direction of liquid flow. Due to the unbalanced radial force and poor sealing, it is mostly used for low-pressure winding.
Spool-type reversing valve is the most widely used hydraulic excavator by relying on the movement of the valve stem in the valve body to control the direction of liquid flow. The number of spool valves depends on the number of working positions of the valve stem in the valve body, which is represented by the number of squares in the system diagram, which is divided into two, three and multiple positions. The number of inlet and outlet ports of the main oil passage on the spool body is called the pass number. Generally, the middle square of the three-position valve represents the middle position of the valve. Slide valve in the middle
The form of the passage at the position is called the spool function. For example, the spool valve functions include O type, H type, M type, etc., as shown in Table 1-3.
In order to facilitate the standardization and serialization of the design and production of valves, often use the same structure of the valve rest, respectively equipped with different structure of the stem, so as to obtain a variety of valves with different functions. Because the production of the valve body is more complicated, adopting the above-mentioned percussion is beneficial to the mass production of the valve body.
For details, please consult Merritt Excavator Repair Center
