The pressure difference before and after the throttle valve in the throttle speed regulating circuit is too small

The pressure difference before and after the throttle valve in the throttle speed regulating circuit is too small

In the system shown in Figure 34, the hydraulic pump is a quantitative pump, and the throttle valve is on the oil inlet road of the hydraulic cylinder, so the system is an oil inlet throttle speed regulation system. The hydraulic cylinder is a single rod hydraulic cylinder, and the reversing valve adopts a three position four-way O-type electromagnetic reversing valve. The check valve on the oil return circuit of the system is used as a back pressure valve. As it is an oil inlet throttle speed regulation system, the overflow valve is normally open during the speed regulation process, playing the role of constant pressure and overflow.

The fault phenomenon of the system is that when the hydraulic cylinder pushes the load to move, the movement speed cannot reach the set value.

After inspection, all components in the system work normally, and the oil temperature is 40 ℃, which belongs to the normal temperature range. The regulating pressure of the overflow valve is 0.3MPa higher than the working pressure of the hydraulic cylinder, and the pressure difference is small, that is, the low regulating pressure of the overflow valve is the main reason for the above failures.

In the throttle valve oil inlet throttle speed regulating circuit, the movement speed of the hydraulic cylinder is determined by the flow through the throttle valve. The flow through the throttle valve depends on the flow cross-section of the throttle valve and the pressure difference between the front and back of the throttle valve. Generally, it should reach 0.2 ~ 0.3MPa, and then adjust the flow cross-section of the throttle valve to stabilize the flow through the throttle valve.

In the above circuit, the pressure loss of the oil passing through the reversing valve is 0.2MPa, and the set pressure of the overflow valve is only 0.3MPa higher than the working pressure of the hydraulic cylinder, which causes the pressure difference before and after the throttle valve to be lower than the allowable value (only 0 ~ 0.1MPa), and the flow through the throttle valve cannot reach the value required by the design, so the movement speed of the hydraulic cylinder cannot reach the set value.

Troubleshooting: increase the regulating pressure of the overflow valve to 0.5 ~ 1.0MPa, make the pressure difference between the front and rear of the throttle valve reach a reasonable pressure value, and then adjust the flow section of the throttle valve, so that the movement speed of the hydraulic cylinder can reach the set value.

From the above analysis, it is not difficult to see that the throttle valve speed regulating circuit must ensure that the pressure difference before and after the throttle valve reaches a certain value. If it is lower than a reasonable value, the movement speed of the actuator will be unstable, and even cause the hydraulic cylinder to crawl.