Created on:2022-04-06 09:11

Adjustment and repair of directional valve

Adjustment and repair of directional valve

1. Introduction

The working principle of the directional valve is that the slide valve moves and shifts in the body and connects the oil circuits in different directions, so as to realize the reciprocating motion of the hydraulic cylinder and the left, right and stop of the hydraulic motor. The telescopic mechanism and luffing mechanism of general truck crane apply three position four-way directional valve; Some hoisting and slewing mechanisms also use three position four-way valves, while others use five position three-way valves or three position six-way valves. The number of reversing positions of the reversing valve indicates the number of different connection states between the oil ports. Among them, the middle working position of the three position four-way valve is called the neutral position. When the directional valve is in the neutral position, the connection of each oil port is an important feature (see the table below).

Slide valve skill code

状态

中位时的性能及用途

O

中间封闭

  各油口全部封闭,系统保持压力;AB两口处于紧锁状态,使工作机构停留在任一位置。适用于一个液压泵供给数个液压缸的液压系统

M

PO连通

  中位时,AB油口封闭,PO连接,可将液压缸或马达锁住在一定工作位置,液压泵来油直接回邮箱,使用该阀的此种形式时可以几个串联使用

 

2. Micro adjustment of the position of the oil port when the manual directional valve is in the middle position

(1) Phenomenon analysis. A QY8 truck crane was replaced with a new valve not long ago due to the serious oil leakage of the original directional valve, but other faults occurred after a short service time. When the valve stem of the directional valve is pulled by hand, it is stopped at about 1 / 5 of the front of the total stroke and the accelerator is increased, there will be abnormal noise. In serious cases, there will be pipe explosion or high-pressure rubber hose falling from the pipe joint. Such faults have occurred several times; If the driver can quickly pull over this position or reduce the throttle when operating the valve stem, this fault can be avoided. The analysis shows that the problem may lie in the dimensional error of an oil groove on the valve stem relative to the position of the oil groove of the valve body (casting), that is, the machining error of the position of the oil return groove of the valve stem or valve body. If so, when the valve stem is pulled slowly and short, the oil inlet and outlet of the valve cannot be opened at the same time within a short distance or even at a certain point at the beginning, that is, the high-pressure oil circuit (incoming oil) has been connected but the oil return circuit has not been connected. At this moment, if the valve stem stops and the accelerator is increased, the pressure will be held until the above fault occurs.

(2) Method for correcting the position of valve stem oil return groove. Methods to eliminate this fault: first, replace the valve with a new one, and second, correct the position of the valve stem oil return groove under neutral working conditions. There are two ways to correct the position of the valve stem oil return groove.

199

1) Method 1. Remove the valve plate in question, clean it, draw the relative position diagram of each oil groove in the inner hole of the valve plate (see Figure 199), find the reference of the neutral position of the valve rod in the valve plate and mark it on the diagram, then measure the exact position and width of the valve rod oil groove and mark it on the diagram, and then draw several working positions of the valve rod one by one through calculation or on the diagram, but it must be accurate, In this way, we can find the position where the oil inlet and outlet controlled by the valve rod cannot be synchronized in an instant. After marking this position on the valve rod, use a grinder or lathe to slightly widen the oil return groove in question, that is, reverse the shoulder blocking the oil return on the valve rod on one side (side) of the oil return groove by 30 ° or 45 °, and the axial side length of the chamfer shall be calculated and determined according to the previous size. It must not be too large, otherwise the directional valve will not be used. According to experience, the side length of chamfer is about 0.5mm, and the maximum can not exceed 0.8mm. If there is no machine tool, this work can also be completed on a grinder with relatively stable rotation.

2) Method 2. If it is inconvenient to adopt method 1, the method of adding round gasket can be used to determine the accurate position of valve stem chamfer (see Figure 200). Two groups of round gaskets with thickness of 0.5mm and 0.8mm are processed in advance, one large and one small in each group. The large gasket is used to move the valve stem and the small gasket is used to prevent the valve stem from moving. The inner diameter of the large gasket for left displacement is slightly larger than the diameter D of the valve stem, and the outer diameter is slightly smaller than or equal to the inner diameter of the rear cover 10 in Figure 199; The outer diameter of the small gasket is slightly smaller than the inner diameter of the inner end of the rear cover 10 in Figure 199, and the inner diameter is equal to or slightly larger than the front diameter D of the valve stem. If you want to move the middle position of the valve stem to the left, put the large gasket behind the reference plane of the spring seat B and the small gasket behind the reference plane of the spring seat (in this way, the neutral position of the valve stem will move to the left, and the valve stem can still maintain no free movement left and right. If only the large gasket is padded, the valve stem will have free movement); If you want to move the valve stem to the right, put the extra large gasket behind the through datum plane of the spring seat and the small gasket behind the datum plane of the spring seat B. in this way, the neutral position of the valve stem will move to the right. After each installation of gasket (there are two kinds of gaskets with two thicknesses moving left and right, and there are four states in total), the installation test must be carried out. The oil groove on the valve stem that hinders the low-pressure oil return (corresponding to chamber a or chamber B) can be found out at most four times; Then, chamfer the shaft shoulder blocking the oil return as in method 1. However, do not forget to remove the added gasket after chamfering; If the valve rod acts normally after adding gasket, it can be used temporarily.

200

3. Repair of reversing valve stem (slide valve) after wear

After the valve rod (slide valve) of the directional valve is worn, the fit gap with the valve body hole increases, the sealing performance at the oil port decreases, the hydraulic system leaks internally, and the bearing capacity decreases (or shifts). If the internal leakage is serious, it will cause accidents. If only one or two valve discs of a multi-way directional valve are seriously worn, the valve discs were replaced after wear in the past. At present, there are more and more repairs. It is economical and technically feasible to repair it. When repairing, first clean the valve body hole and carry out accurate measurement; Then make the grinding mandrel according to the measured size (see Figure 201).

When grinding the valve body hole with the grinding mandrel, first fix the valve body and make the valve body hole vertical, and then put the reinforcement rod through the hinge shaft hole to lift the grinding mandrel. In the process of lifting, pay attention to the left and right rotation, try to grind the hole evenly, and focus on restoring the roundness of the valve body hole. After grinding, accurately measure the hole, make a new valve rod according to the measured size, conduct quenching and tempering treatment, and finally finish grinding and forming; If the original valve rod can be used according to the measured hole size after the valve plate is repaired, use the original valve rod; If the valve rod becomes thinner, it can be repaired by electroplating. Before electroplating, the outer diameter of the original valve rod can be turned to 0.2mm. After electroplating, the valve rod can be ground according to the new size requirements.

201.202

4. Inspection of oil outlet tightness of directional valve

In the luffing mechanism and telescopic mechanism of truck crane, there are four factors affecting the sliding of heavy objects: the sealing ring at the piston is damaged and the hydraulic cylinder leaks; The sealing ring at the head of the pressure relief cylinder is damaged and there is oil leakage along the piston rod; The balance valve is not tightly sealed and has internal leakage; The valve rod of the directional valve is seriously worn, and the seal at the oil port connected with the actuator is not tight. This paper puts forward a simple detection method for the reason of heavy object falling caused by the lax sealing of directional valve. Its working principle is shown in Figure 202.

When it is suspected that the sealing of an oil outlet connected between the reversing valve and the hydraulic cylinder is not tight, the oil pipe of the other m oil outlet connected between the reversing valve and the hydraulic cylinder (luffing cylinder or telescopic cylinder) can be removed and blocked first; Put the reversing valve in the middle position after; Then connect and fasten according to the requirements of figure 202, press the hand pump and bleed through the bleed screw; Finally, pressurize with manual pump and observe whether the value of pressure gauge can reach the standard pressure value of the system (the standard pressure of telescopic and luffing system is 21MPa). If the pressure cannot be added at all or maintained after adding it, and the pressurized hydraulic system does not leak oil, it can be concluded that there is a problem with the directional valve. Oil pipe 3 in Figure 202 is an oil circuit for measuring another oil outlet. Which oil outlet should be measured depends on the actual situation. However, it should be noted that when this method is applied, the crane should be unloaded; The jib must be in the low position; The directional valve must be kept in the neutral position; At the same time, do a good job in other aspects of safety work.

 

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