Due to the structure of the displacement limit, it is generally considered gear pump can only be used as a constant flow hydraulic source. However, the attachment and threaded coupling valve scheme is effective in increasing its functionality, reducing system costs and increasing system reliability, and as a result, gear pump performance can approach that of costly, complex piston pumps. For example, installing a control valve directly on the pump controls the cost by eliminating piping between the pump and the directional valve. Fewer tubing and fittings reduce leakage and improve work reliability. And the pump itself to install the valve can reduce the cycle pressure of the circuit, improve its performance. Here are some of the loops that can enhance the basic functions of a gear pump, some of which are practically proven viable circuits, while others are innovative. Unloading circuit The unloading element will combine the high flow pump with the low power single pump. Liquid is discharged from the outlets of both pumps until a predetermined pressure and / or flow rate is achieved. At this moment, the large flow pump circulates the flow from its outlet to the inlet, thereby reducing the output flow of the pump to the system, that is, reducing the pump power slightly higher than the required value of the high pressure part. The percentage of flow reduction depends on the ratio of unloaded displacement to total displacement at this time. The combination or threaded coupling unloader valve reduces or eliminates the need for piping, ducts and fittings, and other possible leaks. The easiest to uninstall components by hand. The spring causes the unloader valve to be switched on or off, and when the valve is manipulated, the on-off condition of the valve is switched. Lever or other mechanical mechanism is the easiest way to manipulate this valve. Guided (pneumatic or hydraulic) unloaders are an improvement on the way in which such valves can be remotely controlled. The biggest progress is the use of electrical or electronic switch control of the solenoid valve, which can be used not only remote control, and can be automatically controlled by the computer, usually considered this simple uninstall technology is the best case. Manually operated unloading components are commonly used in circuits requiring high flow rates and rapid movements for rapid actuation, requiring large flow and reducing flow for precise control, such as a telescoping boom circuit. Circuit unloading valve without manipulation signal (left position), the circuit has been a large flow output. For normally open valves, the circuit will output a small flow under normal conditions. Pressure sensing unloading valve is the most common program. The spring action puts the unloader valve in its high flow position (left position). When the circuit pressure reaches the preset value of the relief valve, the relief valve is opened and the relief valve is switched to its low flow position (right position) under hydraulic pressure and action. The pressure sensing unloading circuit is used for the stroke to be fast, and the hydraulic cylinder requiring high pressure and low speed at the end of the stroke is for liquid supply. The pressure sensing unloading valve base is basically an automatic unloading element that achieves system pressure relief, commonly used in range finders and hydraulic vices. The unloading valve in the flow sensing unloading circuit is also urged by the spring towards the large flow position (left position). The size of the fixed orifice in the valve is based on the required flow rate for the machine's optimum engine speed. If engine speed exceeds this optimum range, the orifice pressure drop will increase, displacing the unloader valve to the low flow position (right position). Therefore, adjacent components of the large flow pump can be made to the size of the maximum flow throttling, so the circuit less energy consumption, stable and low cost. A typical application of this circuit is to limit the loop flow to the optimum range to improve the overall system performance or to limit the circuit pressure during high speed operation of the machine. Commonly used in garbage truck and so on. The unloading valve of the pressure-flow sensing unloading circuit is also spring-biased to the high-flow position (left-hand position) and will be unloaded regardless of the desired pressure or flow rate. Equipment in idle or normal working speed can be completed under high-pressure work. This feature reduces unnecessary traffic and therefore reduces the power required. Because of this circuit has a wide range of load and speed changes, it is often used in mining equipment.