1. Basic circuit basic circuit is composed of one or several hydraulic components, which can complete specific functions and is the basic unit of the system.
2. Pressure limiting circuit the pressure limiting circuit is used to limit the pressure so that it does not exceed a certain set value, so that the system and components will not be damaged due to overload.
A ground parallel limited pressure valve (overload valve) is often formed on the oil inlet and return circuits of the boom cylinder and the stick cylinder of the excavator to limit the maximum locking pressure of the hydraulic cylinder in the locked state; If this pressure is exceeded, the pressure limiting valve opens for unloading, protecting the hydraulic components and pipelines from damage. For example, when the excavator bucket is digging, the boom must be stressed. In order to maintain normal operation, although the boom hydraulic cylinder is in the "non working state", it must have enough locking force to resist tension or compression. Sometimes, this locking pressure exceeds the maximum working pressure of the system. When the locking pressure is greater than the setting value of the overload valve, the overload valve opens and returns oil to the oil tank. Theoretically, the set pressure of this pressure limiting valve can be independent of the pressure of the hydraulic system. Moreover, the higher the set pressure, the greater the locking force, which is beneficial to mechanical operation. However, the excessive set pressure affects the strength of hydraulic components and the safety of hydraulic pipelines. Generally, the set pressure of the overload valve is 1.25 times of the system pressure.
Speed limiting circuit speed limiting circuit is used to ensure operation safety. Yc13 and yc35 excavators are equipped with one-way throttle valves on the return oil circuit of the boom cylinder cavity in order to prevent the boom from falling too fast due to its own weight. Throttling oil circuit is set on the corresponding oil return circuit of the boom, stick and bucket reversing valve of yc65 and yc85 excavators, which can also prevent the boom, stick and bucket from falling too fast due to their own weight.
Speed limiting circuit
Speed limit circuit is used to ensure operation safety. Yc13 and yc35 excavators are equipped with one-way throttle valves on the return oil circuit of the boom cylinder cavity in order to prevent the boom from falling too fast due to its own weight. Throttling oil circuit is set on the corresponding oil return circuit of the boom, stick and bucket reversing valve of yc65 and yc85 excavators, which can also prevent the boom, stick and bucket from falling too fast due to their own weight.
Braking circuit and buffer circuit of slewing mechanism
The rotary inertia of the excavator is large and the starting and braking are frequent. Special circuits should be used to ensure safety and protect components.
(1) Braking circuit
Rotary mechanism often adopts hydraulic braking, mechanical braking and mechanical hydraulic braking.
Hydraulic braking is to realize rapid braking by cutting off the inlet and outlet oil circuits of the rotary motor and generating a large back pressure on the return oil circuit. Large braking force. Hydraulic braking is adopted for the slewing motor and traveling motor of Yuchai excavator.
(2) Buffer circuit
In order to reduce the excessive impact during braking, two buffer valves are installed on the inlet and outlet oil circuits of the swing motor. When the swing motor suddenly stops or reverses, the pressure oil in the high-pressure oil circuit of the motor is discharged back to the oil tank from the buffer valve, and the low-pressure oil circuit is replenished by the oil replenishment circuit through the one-way valve, so as to eliminate the hydraulic impact.
The swing motor of yc35, yc65 and yc85 excavators adopts the buffer circuit of two buffer valves and two one-way oil makeup valves. The set pressure of the buffer valve is equal to the rated working pressure of the swing motor. The oil makeup pressure of the one-way oil makeup valve is provided by the back pressure valve of the return oil circuit, and the oil makeup back pressure is generally 0.3-0.5mpa.
