Comparison of characteristics between open hydraulic system and closed hydraulic system

January 15, 2019

Features of open hydraulic system and closed hydraulic system Comparison of closed hydraulic system:

1. At present, the closed-type hydraulic system variable pump is an integrated structure. The charge pump and the oil-filling, overflow, and control valve groups are integrated into the hydraulic pump, which makes the pipe connection simple, which not only reduces the installation space, but also It reduces the leakage and pipeline vibration caused by the pipeline connection, improves the reliability of the system and simplifies the operation process.

2. The oil replenishing system can not only ensure the response of the volumetric transmission when the displacement of the main pump is changed, but also improve the operating frequency of the system, and also increase the pressure at the inlet of the main pump to prevent venting cavitation at high flow rates. Improve the pump speed and prevent pump suction, improve working life; the oil system is equipped with filters to improve the reliability and service life of the transmission; in addition, the charge pump can also conveniently supply power to some low-pressure help mechanisms.

3. Since only a small amount of oil is drawn from the fuel tank, the loss of the fuel tank is reduced.
Features of the open hydraulic system:

1. Generally use double pump or three oil supply, the pilot oil is provided by a separate pilot pump.

Some hydraulic actuators require a large amount of power to be combined and supply oil. There are two ways to merge:

1 valve merges.

Generally, a dual pump is combined to supply a valve stem, and the hydraulic actuator is controlled by the general rod of the valve to supply the desired hydraulic flow. The aperture design of the valve stem of the combined flow mode needs to consider the virtual flow area of the multi-pump oil supply.

2 outside the valve.

The two pumps are respectively operated by the respective valve stems through the two valves, and the oil is supplied to the hydraulic actuators of the desired confluence outside the valve stem. Although the steering structure is relatively complex and bulky, the stem diameter is relatively small due to the single pump flow through the valve stem and may be common to other valve stems.

2, multi-way valves are often divided into sections and sub-pumps for oil supply. Each valve group can use two kinds of oil passages, straight through oil supply passage and parallel oil supply passage, according to actual needs. The former can achieve preferential oil supply. When the upstream valve stem is actuated, the pressure oil is supplied to the hydraulic component operated by the valve stem, and the hydraulic component operated by the downstream valve stem cannot be operated. The latter can be achieved and supplied with oil.

3. In order to meet various working conditions and compound action requirements, a simple on-off type two-position two-pain valve and a cartridge valve are generally used to directly lead oil from one oil passage to another, and often adopt a single The valve is prevented from returning to the oil and constitutes a unidirectional passage.

There are two ways to operate the on-off valve:

1 The pilot operated oil linkage operation is adopted, and the pilot control oil controls the operation of the valve stem to move the interlock valve simultaneously.

2 The oil passage is added to the control valve as the oil passage for controlling the on-off valve, so that the opening and closing of the on-off valve is also controlled while the control valve is operated.

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