Reversal function Reversal FuncTIon 5.3.1.1 "Through" and "Position" of directional valve "Port" and "PosiTIon" are important concepts of directional valves. Different "pass" and "position" constitute different types of directional valve. Generally speaking, "two-position valve" and "three-position valve" refer to the spool of the directional valve has two or three different working positions. The so-called "two-way valve", "three-way valve", "four-way valve" means that the valve body of the directional valve has two, three, and four oil passages that are not connected and can be connected to different oil pipes in the system. Interface, different oil passages can only communicate through the switch of the valve port when the valve core is displaced. The structural forms and graphic symbols of the main parts of the spool valve of several different "pass" and "position" are shown in Table 5.1. The meaning of the graphic symbols in Table 5.1 is as follows: (1) Use the box to indicate the working position of the valve. A few boxes indicate how many "positions"; (2) The arrow in the box indicates that the oil circuit is in the connected state, but the direction of the arrow does not necessarily indicate the actual direction of the liquid flow; (3) The symbol "┻" or "┳" in the box indicates that the path is unavailable; (4) If there are several interfaces connected to the outside of the box, it means several "passes"; (5) In general, the oil inlet of the valve connected to the system oil supply path is indicated by the letter P; the oil return port of the valve connected to the system oil return path is indicated by T (sometimes O); and the oil port connected by the valve and the actuator Use A, B, etc. Sometimes, L is used to indicate the leakage port on the graphical symbol; (6) The reversing valve has two or more working positions, one of which is the normal position, that is, the position where the valve core is not subjected to the operating force. The median position in the graphical symbol is the normal position of the three-position valve. The two-position valve using spring return is the normal position with the passage state in the frame close to the spring. When drawing the system diagram, the oil circuit should generally be connected to the normal position of the directional valve. 5.3.1.2 Spool Valve FuncTIon When the spool valve is in the neutral position (Neutral PosiTIon) or the original position (Normal position), the connection mode of the oil ports in the valve is called the spool function of the directional valve. The spool valve function can directly affect the working state of the actuator, and different spool valve functions can meet different requirements of the system. Correct selection of spool valve function is very important. Here we introduce the spool function of two-position two-way and three-position four-way directional valves. Table 5.1 The structure and graphic symbols of the main parts of the different "pass" and "position" spool valve Name Structure schematic diagram Graphic symbol (L) 2 / 2-way valve The two-position two-way directional valve has only two states between the two ports; on or off [see Figure 5.15 (a)]. The automatic reset type (such as spring return) two-position two-way spool valve has two functions: normally closed (O type) and normally open (H type) [see Figure 5.15 (c)] Figure 5.15 Spool function of 2 / 2-way valve Table 5.2 Commonly used spool valve function of three-position four-way valve Type Symbol Status, characteristics and application of neutral port (2) Three-position four-way directional valve There are many types of spool valve functions for three-position four-way directional valves. The common ones are listed in Table 5.1. The middle box represents its original position, and the left and right boxes represent the two commutation positions. The connection methods of the left and right ports are straight-through or cross-connected, so only one letter is used to indicate the central position. In addition, the three-position four-way directional valve has two transition positions. When there is also a requirement for the connection between the oil ports of the directional valve from one station to another station, each oil The connection state of the port and the throttle mode of the valve port can still derive other spool valve functions. In hydraulic symbols, this transitional function can be drawn between each station channel symbol and separated from it with a dotted line. Figure 5.16 shows two different transition functions of O-type three-position four-way directional valve. Figure 5.16 Transition function of three-position four-way slide valve (a) The transitional function that connects T and A (or B) first; (b) The transitional function that connects P and A (or B) first Increasing the transition function will lengthen the spool stroke, which is particularly unfavorable for the electromagnetic directional valve, because the excessively long spool stroke not only affects the reliability of the electromagnetic directional valve, but also extends its operating time, so the electromagnetic spool The directional valve is generally a standard reversing function without a transition function. Only hydraulic (or electro-hydraulic) directional valves are designed for different transition functions. The spool valve of different functions, the valve body is a common part, and the difference is only in the structure of the shoulder of the spool, the axial size and the number of radial through holes on the spool.
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