1. Lock after braking
The gap between the valve plug and the valve body of the steering valve of the truck crane is mostly sealed. Under the dual action of its own gravity and the gravity of the lifting load, the high pressure oil often passes between the spool and the valve body during the braking process. The small gap is slowly leaked, and the hydraulic cylinder or hydraulic motor of each mechanism cannot be effectively locked. Therefore, the hoisting weight is reduced, the boom is retracted, the amplitude is increased, and the legs are sunk. Normal work, but also lead to the occurrence of vicious accidents such as vehicle overturning and casualties. There are at least the following four safety measures to eliminate hidden dangers.
(1) Connect the hydraulic lock in the return line
The reverse oil circuit of the pilot operated check valve may only be connected after it has controlled the oil circuit to input a certain pressure of oil. It is a switching element that can achieve on-off control of the oil circuit, which is commonly referred to as a hydraulic lock. The hydraulic lock is reversely connected in series in the oil return path of the hydraulic cylinder (hydraulic motor), and the control oil passage is connected with the oil inlet pipe of the hydraulic cylinder (hydraulic motor), so that the return oil passage is in the braking state. The control oil circuit is cut off by the action of no pressure oil, and the hydraulic cylinder (hydraulic motor) plays the proper locking function.
The locking effect of the hydraulic lock depends on the shape of the spool and the type of construction of the valve.
If the spool is ball valve type or spool type, the leakage will still be inevitable, that is, the oil may leak through the groove caused by the impact of the spool or the gap between the valve body and the valve body. Therefore, the hydraulic lock spool used in the truck crane should use a cone core with good sealing performance, which can ensure that the oil does not leak even if it is used for a long time.
According to the working condition of the truck crane, the IY-F type high pressure hydraulic lock with unloading valve core should be selected.
For the leg oil circuit, there are two locking requirements: support lock and suspension lock. According to different oil passages, each leg can adopt only one hydraulic control check valve, one-way hydraulic lock that can only act as one-way locking, or two-way hydraulic pressure that is cross-connected by two hydraulic control check valves. lock. The latter option is generally employed. Each leg locking device must be set independently.
(2) Series balancing valve in the return line
The balance valve is essentially a combination valve of a one-way valve and an externally controlled internal release sequence valve. The installation position and the locking principle in the truck crane are exactly the same as those of the hydraulic lock, that is, installed in the return line. Cut off the oil circuit after braking. If there are no other special requirements for the oil circuit, you should try to use a hydraulic lock with a relatively low price.
(3) Improve the sealing of hydraulic components
After installing the hydraulic lock or balancing valve in the oil passage, it is not always possible to completely ensure the locking of the mechanism after braking, and the sealing performance of the hydraulic cylinder (hydraulic motor) is also a key factor that restricts the locking effect.
The leakage of hydraulic components is divided into internal leakage and external leakage. Leakage in the hydraulic cylinder is not easy to detect, which will result in the leg being retracted, the boom telescopic and the variable amplitude 3 mechanism can not be locked and sinking. Therefore, the key to improving the sealing effect of the hydraulic cylinder is to solve the problem of internal leakage occurring inside it.
In general, the amount of oil leakage inside the hydraulic cylinder of a truck crane should be strictly limited. For safety inspection, the moving distance of the piston at the rated pressure shall not exceed 0.5 min within 10 min. If this value is exceeded, the sealing performance is not good, and a new Y-ring should be replaced in time.
(4) hoisting lift hydraulic motor outer brake
It is difficult to see that hydraulic cylinders and hydraulic motors do not cause internal leakage for a long time, and the leakage of the seals after wear is unconsciously generated. Thus, if the lock is firm, there is only one way to install the brake, and it can only be used on the hydraulic motor that lifts the hoisting weight. Others such as the expansion and contraction of the boom can not be used.
The brake that acts on the hoisting and lifting mechanism is actually a small single-bar single-acting hydraulic cylinder. The brake is normally closed and the braking force depends on the spring force in the cylinder. In order to obtain the ideal locking effect, it is of course desirable that the larger the spring force, the better, but the excessive spring force will increase the energy consumption of the brake release brake, so the external brake is an auxiliary means of its locking scheme.
2. Speed ​​limit during exercise
Due to the long lifting of the crane crane, the telescopic expansion of the boom and the variable amplitude of the boom, the acceleration phenomenon caused by the gravity during the downward movement of the mechanism or the load is also a prominent problem. The speed limit for truck cranes is usually the following two methods.
(1) Series balancing valve in the return line
The function of the balance valve can not only lock, but also limit the speed. When the mechanism or the load is lowered, the sequence valve in the balance valve can maintain the steady flow state of the hydraulic cylinder (hydraulic motor) by the balance of the spool, so that the hydraulic cylinder (hydraulic motor) maintains the constant speed movement. In order to obtain a uniform descent speed, two points must be paid attention to when designing the system: First, in order to save costs, simply replace the balance valve with a general one-way valve and an externally controlled internal leakage sequence valve. This is because the balance valve is also a combination of a one-way valve and an externally controlled internal leakage type sequence valve, but the sequence valve has been added with a double-layer spring, a damper small hole and the like to dampen the valve core; the second is the control of the balance valve. The oil circuit is connected in series with the throttle valve so that the spool of the sequence valve operates "hysteresis", and the speed is not changed due to small changes in external pressure. In the speed limit scheme, the effect of using a balancing valve is the most ideal and the preferred method.
(2) Speed ​​limit with manual reversing valve
Among all the reversing valves, only the manual reversing valve can control the opening of the valve port at the same time as the reversing valve, and can also control the speed limit and throttle speed. Therefore, when the vehicle crane mechanism or the load is decelerated, the driver can reduce the degree of pulling of the manual reversing valve handle to reduce the opening degree of the valve port. Of course, the speed limit of the manual reversing valve is not ideal due to the shaking of the driver's hand. However, because the loading and unloading speed of the truck crane is often adjusted according to the specific conditions of the construction site, the movement of the mechanism is often discontinuous. Intermittent operation, so the skilled driver can still receive a certain speed limit effect by manipulating the manual reversing valve.
In short, for the crane hoisting lifting, boom telescopic, boom lapping 3 mechanism has both locking and limited speed requirements, should use the balance valve that can meet both locking and speed limit requirements, and then mechanical brake .
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