A Excavator machine, a: Do the boom action, after the pilot valve handle is reset, the boom will continue to move for a certain distance. b: Or the boom will move to the end automatically after starting.
Analysis: When the operation is stopped and the pilot valve handle is in the neutral position, the directional spool should also be in the neutral position (at this time, the pilot oil ports at both ends of the spool are connected to the fuel tank), if the spool is offset from the neutral position, then the cylinder will have Action, the above fault is obviously caused by the boom reversing spool can not return to the neutral position (or not reset in time).
Reversing spool can not return to the neutral position will cause the above b fault.
Failure to reset the spool in time will cause the above a fault.
(D directional spool can not return to the neutral position is affected by the following three aspects:
1) The spool is stuck. Contaminants and iron filings have stuck the spool.
2) When the operation is stopped, the pilot pressure oil at the one-end of the spool is not drained. This is mostly due to the clogging of the pilot orifice spool damping hole in the pilot oil port at the end of the directional spool.
3) After starting, the pilot pressure oil on the spool-end of the spool is automatically connected. This is because the pilot spool is stuck in the open position. , To determine whether the directional spool is stuck, the pilot pressure oil on the directional spool-end has not been drained or the problem is still the pilot valve, you can start the machine after lifting the left control box. If the fault is eliminated, it is the pilot spool It is stuck; otherwise, the directional spool is stuck or the pilot pressure oil at one end of the directional spool is not drained.
(The spool is not reset in time due to the following two aspects:
1) The pilot pressure oil at one end of the directional spool has a slow pressure relief. It may be that the damping hole of the pilot one-way throttle spool of the directional spool-end pilot oil port is blocked; it may be that the boom pilot spool is reset slowly.
First check whether the pilot oil ports on both ends of the boom directional valve are equipped with pilot one-way throttle valves, if there are, first remove the one-way throttle valve for cleaning, clear the damping hole or cancel the throttle valve core: if the fault is still If there is or is not equipped with a pilot one-way throttle valve, the two pilot hoses of the adjacent normal return switch valve and the two pilot hoses of the boom reversing valve are exchanged. If the action failure of the boom is eliminated, it means that the bucket There is a problem with the rod pilot valve. If the fault still exists, it means that the pilot control is ok, and the rest is the boom directional spool.
2) Movement resistance of spool of directional valve and spring return spring force.
Remove the boom reversing spool and check whether the spool can slide freely and whether the spool return spring is broken (if the spring is broken, the connection between the spool and the spring seat is loose).
