The high pressure gear pump is limited by the structure of the fixed displacement, and it is generally believed that the high pressure gear pump can only be used as the constant flow hydraulic source. However, combination valve attachment into the thread connection scheme for the improvement of its function, reduce the system cost and improve the system reliability are effective, therefore, the performance of the gear pump can be close to the price, complex plunger pump.

 

 

For example, the direct installation of control valve on the pump can save the pipeline between the pump and the direction, thus controlling the cost. Fewer pipe fittings and fittings can reduce leakage, thus improving the reliability of work. And the pump itself installation valve can reduce the circulation pressure of the loop, improve its working performance. Below are some circuits that can improve the basic functions of the gear pump, some of which are the basic circuits that have been proved feasible, while others are innovative.

 

Discharge circuit

 

The unloading element will be combined in a large flow pump with a small power single pump. The liquid is discharged from the outlet of two pumps to achieve predetermined pressure and/or flow. At this point, the large flow pump will flow the flow from its outlet to the inlet, thereby reducing the output flow of the pump to the system, and reducing the power of the magnetic field to slightly higher than the required value of the high pressure part. The percentage of reduced flow rate depends on the ratio of uninstalled capacity to total displacement at this time, and the combination or threaded connection unloading valve reduces or eliminates pipeline, pore and auxiliary parts and other possible leakage.

 

The simplest uninstall element is manually operated. The spring makes the unloading valve turn on or off. When the valve is given a control signal, the valve can be switched off. Leverage or other machinery is the simplest way to manipulate the valve.

 

The pilot control (pneumatic or hydraulic) unloading valve is an improvement of the operation mode, because this valve can be controlled remotely. Its biggest progress is to use an electric or electronic customs control solenoid valve, it not only can use the remote control, and microcomputer automatic control are available, and usually think this simple unloading technology is the best situation for application.

 

Manual unloading elements are often used for high flow and fast operation for quick operation, and to reduce the flow of traffic for precise control, such as a rapid telescopic boom loop. When the unloading of the loop in FIG. 1 shows no control signal (left), the loop always outputs a large flow. For normally open valves, the circuit will output small flow in normal. Pressure sensing offloading is the most common solution. As shown in figure 2, the spring action makes the unloading valve in its large flow position (left). When the circuit pressure reaches the preset value of the overflow valve, the overflow valve opens, and the unloading valve is switched to its small flow position (right) under hydraulic pressure and action. The pressure sensor unloading valve is basically an automatic unloading element that reaches the system pressure, which is widely used in log division and hydraulic vise.

 

The unloading valve in the flow sensor unloading loop is also loaded by the spring to the large flow position (left). The fixed orifice size of the valve is determined by the flow rate required for the optimum engine speed of the device. If the engine speed exceeds the optimum range, the throttle pressure drop will increase, and the unloading valve will be shifted to the small flow position (right). Therefore, the adjacent components of the large flow pump can be the size of the maximum flow throttling, so the circuit has less energy consumption, stable work and low cost. The typical application of this circuit is to limit the flow of the circuit to the optimum range to improve the performance of the whole system or to limit the circuit pressure during the machine's high-speed running. It is often used in garbage truck, etc.

 

The unloading valve of the pressure flow sensor unloading loop is also loaded by the spring to the large flow position (left), which can be unloaded regardless of the predetermined pressure or flow. The equipment can complete high-pressure work under idle or normal working speed. This feature reduces unnecessary flow and reduces the required power. Because the circuit has a wide range of load and velocity, it is often used to excavate the equipment.

 

Has integrated pressure sensor unload power circuit, it is composed of two groups of a quick change of pressure sensor of unloading pump, pump driven by the same prime mover, the two groups each magnetic accept another unloading pump control discharge signal. This way of sensing is called interactive sensing, which allows a set of pumps to work under high pressure while the other pumps a lot of work. The two overflow valves can be adjusted according to the special pressure of each circuit to uninstall one or two pumps. This scheme reduces the power demand, so it can be used with low cost and low cost motive.

 

The load sensing unload circuit is shown. When the control valve (lower cavity) of the main control valve is not loaded, all the flow of the pump goes through valve 1 and valve 2 to the fuel tank; When the load sensing signal is applied to the control valve, the pump is supplied to the loop. When the output pressure of the pump exceeds the pressure predetermined value of the load sensing valve, the pump only provides the working flow to the circuit, while the excess flow passes through the throttle position of valve 2 (upper) to the fuel tank. The gear pump with load sensing element has the advantages of low cost, high anti-pollution ability and low maintenance requirement compared with plunger pump.

 

Priority flow control

 

No matter the speed of the pump, the working pressure or the flow rate required by the branch, the constant flow control valve can guarantee the flow of the equipment. In the circuit shown in FIG. 7, the output flow of the pump must be greater than or equal to the amount of flow required for an oil circuit, and the secondary flow can be used or returned to the tank. The constant value of a flow valve (proportional valve) combines a control with the hydraulic pump, saves the pipeline and eliminates the leakage, thus reducing the cost. The typical application of this type of gear pump circuit is the steering mechanism often visible on the car crane, which saves a pump.

 

The function of the load sensor flow control valve is very similar to that of the fixed-value flow control: that is, no matter the speed of the pump, the working pressure or the flow size of the branch, it provides a flow rate. However, the proposed scheme only provides the required flow rate to an oil channel through a single oil port until its maximum adjustment value. This circuit can replace the standard one flow control loop and obtain the maximum output flow. The pressure of the no-load circuit is lower than the fixed value one flow control scheme.

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