Sequence valve failure principle

I. Introduction The sequence valve is a pressure control valve that uses the pressure of the inlet oil circuit itself to control the sequence of two or more actuators in the hydraulic system. When the pressure at the inlet fails to reach the pressure set in advance by the sequence valve, the sequence valve closes; when the pressure preset by the sequence valve is reached or exceeded, the valve opens and the fluid enters the secondary pressure circuit from the outlet. The next actuator action acts as a switch. If the outlet pressure oil is returned to the tank, it constitutes an unloading valve.

Sequence valve according to the structure and working principle can also be divided into direct-acting and pilot; according to the control of oil into the internal control and external control. The structure of the sequence valve is basically similar to that of the relief valve and the relief valve, but since the ports P1 and P2 are all pressure oil, the drain port L of the sequence valve is connected to the slewing tank separately from the outside of the valve. The sequence valve and check valve combine to make a one-way sequence valve.

Second, the failure analysis and exclusion (A) the set value is not stable, can not be the order of the action of the actuator, or the order of the disorderly movement of the valve in the hydraulic system is the use of system pressure to control the other hydraulic components (such as the cylinder) action sequence When the system reaches the setpoint (setpoint), the sequence valve opens for automatic control.

In a control circuit in which multiple cylinders (two or more cylinders) controlled by a sequence valve operate in sequence, if the set value of the sequence valve is unstable, normal sequential operation cannot be achieved.

(2) When the system does not reach the working pressure set by the sequence valve, the pressure oil flows out from the secondary port. 1 The main valve plug and the valve hole have a large clearance, or the clearance is too large due to wear over time. The pressure oil on the side P1 is leaked to the secondary side, so that the pressure on the secondary side is increased. With spring force, the sequence valve may be opened. At this time, although the pressure of the P1 chamber does not reach the regulating pressure of the sequence valve, two There is also fluid outflow on the secondary side. At this point the main spool can be repaired or replaced and a reasonable assembly clearance is guaranteed.

2 Internal leakage due to other causes.

(C) When the set value is exceeded, the sequence valve does not open. 1 The main valve spring is misfitted into a hard spring.

2 The control piston is stuck.

3 When the heavy equipment is being repaired and reinstalled, the control piston is leaked. As a result, the control pressure oil is relieved by the valve core damping hole through the drain hole, the main valve core is closed under the action of the spring force, and the valve core cannot be opened.

(4) The pressure fluctuation is large and the pressure swing is large According to the standard of JB2146-77, the allowable error of the pressure swing of the X-B low pressure sequence valve is ±0.2Mpa, the pressure of the X type intermediate pressure sequence valve is ±0.3Mpa, and that of the XF type The sequence valve is ±0.5Mpa. Exceeding this standard provides large pressure swing. If the pressure swing is too large, it will also cause malfunctions or non-sequential actions.