The high flow pump circulates the flow from its outlet to its inlet, thus reducing the pump's output to the system, that is, reducing the magnetic power to a value slightly above that required for the high pressure part of the operation. A typical application of this gear oil pump circuit is the steering mechanism commonly found on truck cranes, which eliminates a pump
1. Priority flow control of high pressure gear oil pump
It has a power comprehensive pressure sensing unloading loop, which is composed of two groups of slightly changed pressure sensing unloading pump, two groups of pumps driven by the same prime mover, each magnetic accept the other unloading pump control unloading signal. The size of the fixed throttle hole in the valve is determined according to the flow rate required for the optimum engine speed of the equipment. Compared with 3G three screw pump, the gear oil pump with load sensing element has the advantages of low cost, strong anti-pollution ability and low maintenance requirements. The spring makes the unloading valve on or off, and when the valve is given a control signal, the state of the valve is switched. Here are some of the basic circuits that can improve the basic functions of gear pumps, some of which are proven and some of which are innovative. For normally open valves, the loop will output a small flow under normal conditions. The pressure sensing unloading valve is basically an automatic unloading element to reach the pressure of the system. It is commonly used in log splitting and hydraulic vice. This type of gear pump circuit is commonly used in garbage truck or power steering pump circuits where hydraulic control is limited to achieve optimum engine speed, and in stationary machinery.
For bypass flow control, regardless of pump speed or working pressure, the pump always according to the predetermined maximum liquid supply to the system, the excess part is discharged back to the tank or pump inlet. When the circuit pressure reaches the pre-set value of the relief valve, the relief valve opens, and the unloading valve switches to its small flow position (right position) under hydraulic pressure and under action.
The manually operated unloading element is often used in the loop which needs large flow for fast operation and the loop which needs large flow for fast operation and reduces flow for precise control. The high-pressure gear oil pump, for example, the loop of fast telescopic boom.
The unloading valve of the pressure flow sensing unloading loop is also operated by the spring pressure to the large flow position (left position), and will be unloaded whether the predetermined pressure or flow is reached.
Regardless of pump speed, working pressure or branch flow size, fixed value of a flow control valve can always ensure the required flow of equipment work.
. Therefore, the adjacent components of the large flow pump can be made to the size of the maximum flow throttling, so the loop has less energy consumption, stable work and low cost. This circuit can replace the standard primary flow control circuit to obtain the maximum output flow. This feature reduces unnecessary flow, thus reducing the power required. This scheme limits the flow of the system so that it has the best performance. This type of sensing is called interactive sensing, which enables one set of pumps to operate at high pressure and another at high flow. The percentage of flow reduction depends on the percentage of ununloaded volume at the time of discharge. Combined or threaded unload valves reduce or eliminate piping, holes, accessories and other possible leaks. Such loops are typically used to limit loop flow to an optimal range to improve overall system performance, or to limit loop pressure during high-speed machine travel. Because of its wide range of load and speed variations, this loop is often used in excavating equipment. The gear oil pump can only be used as a constant flow hydraulic source because of the structural limitation of constant displacement.
2. Selection of high pressure gear oil pump scheme
Bypass flow control valves can be designed with medium load sensing control valves that limit the working flow (working speed) range. Pressure sensing unloading is the most common solution. And the pump itself installed valve can reduce the loop circulation pressure, improve its performance. It is effective to improve its function, reduce the system cost and improve the reliability of the system. Therefore, the performance of the gear oil pump is close to the expensive and complex plunger pump. If the engine speed is outside this optimum range, the throttle hole pressure drop will increase and the offload valve will be moved to the low flow position (right position). When the unloading of the loop has no operation signal (left bit), the loop has been output large flow.
The offloading element will be combined in a high flow pump with a low power single pump. The equipment can work under high pressure under idling or normal working speed. Load sensing flow control valve and primary flow control valve, its typical application is power steering mechanism. The fluid is discharged from the outlet of the two pumps and the high-pressure gear oil pump reaches the predetermined pressure and/or flow rate. Because the pressure of the no-load loop is lower than the fixed-value primary flow control scheme, the temperature rise of the loop is low and the no-load power consumption is small. This scheme reduces the power requirements, so the use of small capacity cheap prime mover. Constant value primary flow valve (proportional valve) combines primary control with hydraulic pump, eliminating pipeline and eliminating external leakage, thus reducing costs. Its advantage is that the maximum flow rate can be controlled by loop scale and the cost can be reduced. Combine the pump and valve into a whole, and through the pump bypass control, so that the loop pressure is reduced to the minimum, from the surface to reduce the pipeline and its leakage. Fewer fittings and connections reduce leakage and improve reliability.
At present, the gear pump working pressure, function, reduce the system cost and improve the reliability of the system has been close to the plunger pump, combined load sensing scheme for the gear pump provides variable possibilities, which means that the original clear boundary between the gear pump and the plunger pump becomes more and more blurred.
The simplest unloading element of high pressure gear pump is manually operated. Often used in garbage trucks, etc. In this loop, the output flow of the pump must be greater than or equal to the required flow of the primary oil route, and the secondary flow can be used for it or back to the tank. Two relief valves can be adjusted to the special pressure of each loop to unload one or two pumps. Reasonable choice of hydraulic pump scheme one of the determinants, is the cost of the whole system, compared with the price of the piston pump, gear pump with its low cost, simple loop, low filtration requirements, has become a practical choice for many applications. A lever or other mechanism is the easiest way to operate the valve.
The unloading valve in the flow sensing unloading loop of high pressure gear oil pump is also pressed to the large flow position by the spring (left).
3. Bypass flow control of high pressure gear oil pump
The function of load sensing flow control valve is very similar to the function of fixed flow control: that is, no matter the speed of the pump, the working pressure or the size of the branch pumping flow, all provide a flow.
4. Unloading loop of high pressure gear oil pump
High pressure gear oil pump temperature pressure principle, gear oil pump production, directly installed on the pump control valve, can save the pipeline between the pump and the direction, high pressure gear oil pump so as to control the cost. Spring action puts the offload valve in its high flow position (left).
