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First, let’s take a look at the pressure regulating process of the relief valve:
The relief valve screw is fully loosened, the equipment is running, slowly tighten the screw, look at the pressure gauge, stop after raising the pressure for a few MPa, let the equipment run stably under this pressure for a few minutes, and then repeat the process of raising the pressure and running until the adjustment is made. to the set pressure.
There will be a relief valve at the oil pump outlet of each hydraulic system. Sometimes, for some reasons, the pressure at the pump outlet may be greater than the pressure required by the system. At this time, a relief valve is needed to relieve the excess pressure and drain the oil. back to the tank.
The pressure of the relief valve rises but does not rise? why? Here’s an analysis of the reasons:
The phenomenon that the pressure of the relief valve rises but cannot rise to a higher regulating pressure is as follows: although the pressure regulating handwheel is fully tightened, the pressure cannot continue to rise after it only rises to a certain value, especially when the oil temperature is high. . The main reasons are as follows.
(1) The temperature of the hydraulic oil is high, and the internal leakage increases.
(2) The internal parts of the hydraulic pump are worn, the internal leakage increases, and the output flow decreases; the pressure rises, the output flow is smaller, and the flow demand of high load cannot be maintained, and the pressure rises to less than a large pressure. And the performance is that after the pressure is adjusted, the pointer of the pressure gauge fluctuates violently, the fluctuation range is large, and the pressure of the relief valve cannot be adjusted up.
(3) Larger dirt particles enter the damping or bypass holes of the main spool, partially blocking the small holes, reducing the pilot flow entering the pilot valve, and it is difficult to establish a higher pressure in the upper cavity of the main spool to balance The pressure in the lower chamber of the main spool prevents the pressure from rising to a higher level.
(4) Due to the loose fit between the main spool and the valve body hole, strain, grooves, or serious wear after use, part of the oil flow entering the spring cavity through the damping hole of the main valve flows to the oil return port through this gap. (such as Y-type valve, two-section concentric valve); for YF-type and other three-section concentric valves, due to the wear of the sliding joint surface of the matching hole between the main valve core and the valve cover, the matching clearance is large, and the spring cavity enters the spring cavity through the damping hole of the main valve. The flow through this gap and then return to the tank through the spool hole.
(5) The wear and tear between the pilot poppet valve and the valve seat is caused by dirt, moisture, air and other chemical substances in the hydraulic oil, which cannot be well sealed and the pressure cannot rise to a high level.
(6) There is a gap in the contact surface between the pilot poppet valve and the valve seat. Or out of round into a jagged shape, so that the two cannot be well sealed.
(7) The thread of the pressure regulating handwheel or the adjusting screw is bruised or strained, so that the pressure regulating handwheel cannot be tightened to the limit position, and the pilot valve spring cannot be fully compressed to the proper position, and the pressure cannot be adjusted to a higher level. big.
(8) The pressure regulating spring cannot be adjusted to a higher pressure due to the wrong installation of the pressure regulating spring into a soft spring, or due to the decrease in stiffness of the spring due to fatigue, or due to breakage.
(9) The main valve core is stuck at a small opening due to burrs, tapers or dirt on the main valve body hole or the outer circle of the main valve core, and it is in a slightly open state that is not fully opened. At this time, although the pressure can be adjusted to a certain value, it cannot be increased.
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