Created on:2021-09-25 14:30

Lifting and transportation equipment_ Maintenance of truck crane_ Adjustment of directional valve

Lifting and transportation equipment_ Maintenance of truck crane_ Adjustment of directional valve

The working principle of the directional valve is that the slide valve moves and shifts in the valve body to connect 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 mechanism and slewing mechanism also use three position four-way valve, and some use three position five-way valve or three position six-way valve. The number of reversing positions of the reversing valve indicates the number of different connection states between the oil ports, among which 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).

 

The connection condition of each oil port when the two directional valves are in the middle position

Slide valve skill code

状态

中位符号

中位时的性能及用途

O

中间

封闭

img1

各油口全部封闭,系统保持压力;A、B两口处于锁闭状态,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

P、O

连通

img2

中位时,A、B油口封闭,P、O链接,可将液压缸或马达锁住在一定工作位置,液压泵来油直接回油箱。使用该阀的此种形式时可以几个串联使用

 

Micro adjustment of oil port position when manual directional valve is in neutral position

There is a QY8 truck crane in a steel wholesale department. Not long ago, a new valve was replaced due to the serious oil leakage of the original directional valve, but other faults occurred after a short service time. When the valve rod of the directional valve is pulled by hand, 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 off 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 be caused by the dimensional error of an oil groove position on the valve stem relative to the oil groove position of the valve body (casting), that is, the machining error of the oil return groove position of the valve stem or valve body. If so, when the valve rod 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 return oil circuit has not been connected. At this moment, if the valve rod stops and the accelerator is increased, the pressure will be suppressed, resulting in the above failure.

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.

① Method I 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 E), find the reference of the neutral position of the valve rod in the valve plate and mark it on the diagram, then measure the accurate 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 can not be synchronized in an instant. After marking this position on the valve rod, use a grinder or lathe to slightly widen the problematic oil return groove, 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 determined according to the size calculation. It must not be too large, otherwise the directional valve will not be used. According to experience, the chamfer side length 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.

E.jpg

② Method II if it is inconvenient to adopt method I, the accurate position of valve stem chamfer can be determined by adding round gasket (see Figure f). 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 valve stem diameter D, and the outer diameter is slightly smaller than or equal to the inner diameter of the rear cover 10 in Figure E; The outer diameter of the small gasket is slightly smaller than the inner diameter of the rear cover 10 in Figure F, and the sound is small, 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 neutral position of the valve rod to the left, pad the large gasket behind the reference plane of the spring seat B and the small gasket behind the reference plane of the spring seat a (in this way, the neutral position of the valve rod will move to the left, and the valve rod can still maintain no free movement left and right. If you only pad the large gasket, the valve rod will have free movement); If you want to move the valve stem to the right, pad the large gasket behind the spring seat reference plane a and the small gasket behind the spring seat reference plane 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 shall be carried out. The oil groove on the valve rod that hinders the low-pressure oil return (corresponding to chamber a or chamber B) can be found out for up to four times; Then, chamfer the shaft shoulder blocking the oil return as the method worker, but do not forget to remove the added gasket after chamfering; If the valve rod acts normally after adding gasket, it can be used temporarily.

F.jpg

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