Analysis and elimination of hydraulic fault in truck crane
1. judgment and removal of hydraulic throttle fault on truck crane
(1) a fault phenomenon of a 16t crane has a special fault in the lifting of the 8t weight, load at 200mm above the ground. No matter how the engine throttle to increase, the lifting speed is very slow, if 10t load, almost stop lifting. The original design standard of the hoisting speed of the machine is that when the 5 magnification is used, the load lifting speed is 12m/min, that is to say, every 5S should be 1m. Inspection found that the sound of the idling engine and the lifting speed of the hook in the no-load condition are normal. What is the cause of the increase in load when the lifting speed does not go?
(2) the reason analysis in accordance with the usual logic, in the case of overloading, when hoisting speed is slow or stop, the factors involved are the following: the power of engine oil pump, the total efficiency, the lifting motor function, multiway valve and hydraulic oil pressure and so on. By checking and testing, it is determined that the engine, the oil supply pump, the lifting motor and the multiple reversing valve on the engine are all right. Problems of hydraulic oil in the crane on the throttle, and the hydraulic oil is the use of units of their own reform: when the car hydraulic throttle control oil mixed in the air or oil can make the control oil pressure is insufficient, the speed of the engine can not improve, resulting in the lifting power shortage, rising speed influence.
It is found that there are three main reasons for the malfunction of the hydraulic throttle control circuit. When the hydraulic oil is added to the pipeline, the air can not be discharged in time or can not be discharged. There is always a small amount of air in the pipeline. (II) there is a slight crack in the oil pipe wall of the oil pipeline; under the working condition, with the increase of the compression density of the oil, there is a leakage phenomenon, and the proper working pressure is reduced. In the oil pipeline, both ends of the metal pipe joint have dirt, and the crack at the expansion mouth is not smooth, and the joint surface is not smooth, so that the joint is not sealed tightly and has slight leakage. These will affect the hydraulic throttle on the engine control function.
(3) the method of judging the pipeline of the hydraulic accelerator on the truck crane, as shown in figure 21-1. As the center of the system under the rotary joint position to the engine governor a circuit which is not conducive to observation, must be drilled into the body below to see down the tubing side effect on fault judgment, to determine as follows: 1. This work by 3 people at the same time. A nail on the ground as a command, and is responsible for the binding anvil and do some test code records; B in the car control room, control control handle, but not control car throttle; C off in the control room, only responsible for handling off the throttle, throttle is off because of rigid connection in bundled load. By a command from C fuel door, the engine running after lifting a B control handle, lifting the observation and record, find abnormal. A command, observation and recording on the ground; B in the car handle handle and increase the gas; C in the diesel engine next to observe the governor's work. When the throttle is increased, the load is stopped or the lift is slow, the sound of the diesel engine will change, and the governor is unstable at the same time.
(4) the Countermeasures of exclusion
1) exclude the air from the side hydraulic line. As the crane's hydraulic throttle pipeline is relatively long, the pipe diameter relative to the length is too small, so the exhaust is not easy, need to be patient and meticulous work. In the exhaust pipe joint, to the front position as far as possible to raise the oil, near the center part of the rotary joint is lower than that of the front as much as possible so as to exhaust.
2) the tubing shall be cleaned before installation and air pressure tested. One end of the tubing is sealed with a joint, and the other end is connected with the pipeline of the air compressor. After inflation, put people in the water to check whether the pipeline leaks. In the on-site maintenance or commissioning, one of the most simple method is to rub the surface of the pipe clean, end seal, the other end by smoking sprayed into a smoke, if the wall cracks, cracks in the smoke will, on a sunny place, will see more clearly. The air pump for lifting the crane can also be used as an air source for air pressure test. Locate the crack, or weld it, or replace it.
3) the opening at the ends of the pipe is prone to crack. If necessary, remove a small part, and then re open the system.
Trouble removal of hydraulic steering of 2.TL-250E truck crane
A TL 25OE truck crane TADANO turn heavy, difficult fault.
The hydraulic steering principle of this machine is shown in figure 21-2. It is a split hydraulic power assisted system. It is mainly composed of vane pump, throttle valve, safety valve, control valve and power assisted cylinder. The rated working pressure of vane pump is 12.5MPa, the displacement is 17ML/r, and the speed is 370~3700r/min. After preliminary examination, the lubrication of the steering gear is normal, without abnormal noise and wear. Then from the tank began to inspect: oily, oil and oil filter were normal, remove the safety valve and throttle valve check vane pump on the results are normal; the disintegration of vane pump, because there is no standard data and measurement tools, the naked eye can not see the problem; the dismantling of the control valve and the cylinder does not help. Found the problem. After replacement, replace the new oil (No. 8 hydraulic transmission oil), the failure is still as before. But in the disassembly of vane pump a phenomenon makes people doubt that when taking out the rotor from the vane pump, blade immediately from the rotor slot completely slipped out, make people feel the blade groove on the rotor clearance is too large, the vane pump failure. To this end, the oil circuit is disconnected at the A in Fig. 21-2, and the pressure gauge is connected at the front of the disconnection and the pressure test is carried out. When the engine speed is rated speed, the starting oil pressure is 10Mpa, 5min after 9MPa, 8min after 6MPa, 10min after only 4MPa and, and the standard value should be 12.5MPa. The oil pressure decreased gradually with the prolonging of time of the phenomenon, that with the extension of time, the oil temperature rising (when the temperature of 30 degrees, oil viscosity decreases, and the gap of blade and slot ultra serious job pump discharge caused by the pressure gradually decreased, the front confirmed the judgment is correct. After the replacement of the new vane pump, the fault disappears.
Failure analysis of hydraulic support for hydraulic support of 3.QZ-8 model automobile tray machine
(1) the working principle and the fault phenomenon diagram 21-3 are the hydraulic system diagram of the QZ-8 bus crane's outrigger. Because the automobile tire bearing capacity is limited, and as an elastic body in the lifting operation before will bring down the front and back legs, making the car tire with overhead, legs bearing, in order to ensure safe operation, when the car is running, and will be, leg up.
When the manual valve A in the left position when the rod chamber pressure oil pump output by A valve and hydraulic one-way valve into the front leg of the hydraulic cylinder, pushes the piston down, the front leg down; when the valve is located on the right A when working oil pressure and hydraulic control valve A the one-way valve into the front leg of the hydraulic cylinder rod chamber, push the piston upward, the front leg up. In order to ensure
When the supporting leg is parked at any position, the utility model can be reliably locked, and a double hydraulic lock composed of a hydraulic control check valve is arranged in the oil circuit. When the valve A is in the middle, the hydraulic pump is unloaded.
The manual reversing valve B is used to control the movement of the rear leg hydraulic cylinder, and the operating principle is the same as that of the front leg hydraulic cylinder.
System in the course of work, although down the front and rear legs, but can not lift the body, so that the tires overhead.
(2) inference analysis from the fault symptoms to identify the real cause of the failure, can be carried out according to 3 steps: (L) from the fault symptoms, infer the essential reason of fault; (2) from the nature of the reasons for failure, a common inference may lead to failure; (3) from the real reason common causes of faulty reasoning.
The hydraulic cylinder moves the miasma, the essential reason is the lack of oil cylinder hydraulic pressure or resistance to motion is too large, so that the hydraulic cylinder can drive the load movement. Hydraulic cylinder, relief valve, reversing valve, pipeline system and hydraulic pump may fail, resulting in insufficient pressure; and some aspects of the fault may be caused by different reasons. The hydraulic cylinder of serious oil spill, heavy load or friction resistance is too big, the oil inlet is blocked will cause insufficient pressure; pressure relief valve adjustment is too low, the main reason for failure of valve spring (Guide) or soft, pilot valve and main valve seat seal bad heart orifice plug can also cause insufficient pressure; reason the valve can not change, oil shortage, oil plug, still can make the insufficient pressure; hydraulic pump is the power component, insufficient or low volume efficiency of the pump flow, will also make or insufficient pressure, that can't push the load. Hydraulic pump speed is not enough, the pump mixed air, displacement is too small or suction port leakage will make the pump flow is insufficient; the pump seal failure, the pump friction serious wear and tear will make volumetric efficiency too low. After a certain understanding of the law in the event of failure, you can draw the block diagram of fault analysis, the purpose of which is to field failure analysis and troubleshooting process determined by the reasonable way and step down, in order to seek the best way, the real reason to find out one or several faults from possible common fault reasons in use the reasoning method, analysis of the block diagram as shown in figure 21-4 automobile crane outrigger retractable hydraulic system fault. The common reasons for the failure to be deduced from the nature of the failure step by step depend on the study of theoretical knowledge and the accumulation of working experience.
(3) there are several methods for on-site inspection of field inspection methods:
1) instrument analysis. When the hydraulic system fails, the performance of the hydraulic device must change, and this change will be characterized by the characteristic parameters. The characteristic parameters of pressure, flow, temperature, velocity, executive mechanism of noise, oil condition (pollution degree, viscosity) and leakage, of which the most important parameters of pressure, its variation on hydraulic device status is very sensitive. It is the most common fault detection method to determine the state of the system by measuring the pressure of the relevant parts of the system. When measuring different parameters, different testing instruments should be chosen according to the requirements of field conditions and control accuracy.
2) partial stop method, that is, temporarily stop some work of the hydraulic system, observe the influence of the symptoms of the fault.
3) try to prove to the contrary, that is, to try to change part of the working conditions in the hydraulic system, and to observe the influence on the symptoms of the symptoms. If the hydraulic cylinder does not move, remove the external load of the hydraulic cylinder, and observe whether the hydraulic cylinder can operate normally, it can prove whether the hydraulic cylinder does not move because the load is too large.
4) comparison method, that is, the use of standard or qualified components instead of the same components in the system, through the comparison of the working conditions, to determine whether the replacement of components is invalid.
(4) reasoning diagnosis example
1) according to the principle of "from simple to complex", from "easy to difficult", first check the oil quantity of the tank, the leakage of the hydraulic cylinder, and whether the filter and the pipeline are blocked. After examination, we can see that the tank is full of oil, there is no leakage of the hydraulic cylinder, the filter and the pipe are not blocked.
2) check the hydraulic cylinder fault. Because the leg hydraulic cylinder can be laid down and retracted, the reversing valve can be reversed and the hydraulic cylinder is not jammed. Using the "trial and suppression" method, the leg hydraulic cylinder is put down, but not the ground, stationary for some time, the hydraulic cylinder piston is still in situ, indicating that the hydraulic cylinder without leakage, the hydraulic cylinder without fault.
3) check the overflow valve fault. First, check if the adjustment pressure is too low. The "instrument analysis method", an overflow valve is fully open, start the hydraulic pump and valve A in the left position, gradually tighten the overflow valve pressure regulating handwheel, observe the change of the pressure gauge: no matter how tight pressure regulating handwheel, the maximum pressure gauge indicates only 6 of a state, can not reach the working pressure 21MPa pump, which shows that the pressure does not go on.
Relief valve pressure is not high, may be overflow valve failure, or other reasons. In order to avoid the overflow valve qualified inspection, using the "comparison method", the overflow valve is removed, replaced with the type of backup overflow valve, repeat the inspection process, found that the maximum pressure adjustment is still only 6MPa. Thus, the flow valve is no fault.
4) check the hydraulic pump fault. After excluding the possible cause of the failure, it is concluded that the actual cause of the failure is in the hydraulic pump.
Remove the hydraulic pump, check the disintegration, see the cylinder and the valve plate, plunger and cylinder have varying degrees of wear and tear. Wear and tear caused serious leakage of hydraulic pump, hydraulic system pressure can not go up, resulting in outrigger hydraulic cylinder can not hold up the body. For a hydraulic pump of the same type, the fault can be eliminated.
