First, try the action
This refers to a variety of single actions. First, start from the bottom, try the dozer blade, and do it up and down. See if it hits the structure or ca n’t reach the head at all. Can lift the whole machine, stay for a few minutes when lifting, see if there is automatic lowering, if there is leakage in the cylinder or valve core; try walking again, first advance about 10 meters at the same time, and then back about 10 meters at the same time See if there is an obvious deviation, if there is an obvious deviation, the oil path is not uniform, and maintenance is required. Then walk unilaterally, move forward and backward, and see if it can be successful. Normally, you should be able to walk unilaterally at medium speeds. (It is common to not be able to walk unilaterally at idle speed, and is generally not included in the scope of failure).
Try the turning action again. There should be two kinds of fast operation and slow operation when trying the turning operation. Is the turning response too slow or too fast during slow operation? Too slow means that the pilot handle has not been turned after one third of the stroke. Action, too fast means that the pilot handle starts to move slightly at the beginning, and the turning action starts immediately. The response is too fast. You must also test the turning brake performance. After the handle stops operating, how many degrees should the turning action turn, some of the braking performance may be poor. It stops after turning 180 degrees. This is a problem. It is necessary to deal with it. Personally, I think that the braking range of second-hand excavators is generally less than 45 degrees, which are considered acceptable. Retry the action of bucket, stick, and boom. There is no strict standard for the speed. It is generally felt by the hand, but it can be provided here for reference: Take Yuchai's YC230-8 as an example, the bucket extends and retracts the entire stroke for about 3 seconds, and the arm extends and retracts the entire stroke for about 4.5 seconds. The arm is raised or lowered from the lowest to the end, about 5 seconds. Generally, the hand can directly feel the movement too fast or too slow. Too fast or too slow is a problem. Too slow will affect efficiency. Too fast and easy to damage the machine should be repaired and the value will be reduced.
Test tightness
All the moves of the bulldozer can be tried, but the point of trouble is to walk. You can only try on the ramp. Stop on the ramp for about 20-30 degrees and stop for half an hour. If there is something leaking in the motor, it will slide automatically. Now, the turning action tests the brake angle. The tightness of other working devices can be tested as follows: Turn the working device to the other direction of the bulldozer, lift the bulldozer one end, and lift the work device. Pay attention to each cylinder Force, and then jack to mid-air, if there is no bulldozer machine, dig a bucket of mud (or an object of similar weight), close the bucket, extend the stick, and extend the boom to the highest (higher (You can also). If you put it aside, you can go to the room to drink tea. Wait for half an hour before seeing which cylinder has a large stroke change. Personally, I think that excavators that work for thousands of hours generally have a stroke change of less than 10 cm after half an hour If it exceeds, there will be serious internal leakage, which needs to be dealt with. If there is internal leakage, the value will decrease again;
Third, measuring pressure
This is the key, and it is difficult to do, because a non-professional second-hand excavator appraiser may not have a pressure gauge and a pressure measuring joint when he goes to the machine. It can only be lifted by the method of point 2 above. To estimate whether the hydraulic system is sufficient or not, if a professional second-hand excavator evaluation will measure each action, the pump pressure, pilot pressure, and return pressure will be measured once. If the pump pressure is insufficient, the strength will be insufficient. Weakness. If the oil return pressure is too large, the temperature measurement will easily rise. If the pressure is too small, the oil will not be replenished. This will affect the work of the parts that need to be replenished. For machines above 13.5 tons, about 31.5MPa is required, and the following are 16-27MPa, depending on the size of the model, the pilot pressure is generally 3.5MPa-4MPa, and the return pressure is generally 0.3MPa-0.5MPa. Cause or need repair.
