A viable circuit to improve the basic functions of a gear pump

Due to the structure of the limited displacement, usually that the 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 eliminates the need for piping between the pump and the directional valve, controlling costs from the surface. Fewer tubing and connections reduce leakage and improve operational 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.

Uninstall the 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 operation for rapid operation, requiring large flow and reducing flow for precise control, such as a telescopic boom circuit. When the unloading valve of the circuit shown in Fig. 1 has no operation signal, the circuit always outputs a large flow rate. On the normally open valve, under normal circumstances the circuit will output a small flow.

Pressure sensing unloading valve is the most common program. As shown in Figure 2, the spring acts to place the unloader valve in its high flow 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 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 unloader valve is basically a self-unloading element that achieves system pressure relief, commonly used in the range finder and hydraulic vise.

The unloader valve in the flow sensor unloading circuit is also urged by the spring to a large flow rate. The size of the fixed orifice in the valve is based on the required flow rate for the machine's optimum engine speed. If the engine speed exceeds this optimum range, the orifice pressure drop will increase, displacing the unloader valve to the low flow position. Therefore, adjacent components of the large flow pump can be made to throttle the maximum flow size, so the circuit less energy consumption, work steadily and reduce costs. A typical application of this circuit is to limit the amount of circuit 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, unloading no matter whether the pressure reaches the preset pressure or the 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 loop has a wide range of load and speed, often used to excavate equipment.

Figure 5 is a power-integrated pressure sensing unloading circuit, which consists of two groups of pressure-sensing unloading pump slightly change the composition of the two groups of pumps driven by the same prime mover, each pump plus a unloading pump pilot unloading signal people. This type of sensing is called interaction sensing, which allows one set of pumps to operate at high pressure and the other to operate at high flow rates. Two relief valves can be adjusted for each circuit's special pressure to unload one or two pumps. This program reduces the power requirements, it can be low-cost prime mover.

Figure 6 shows the load sensing off-load circuit. When the main control valve cavity (lower chamber) no load sensing signal, the pump all the flow through the valve 1, valve 2 row back to the tank; when the control valve to apply a load sensing signal, the pump to the circuit for liquid; When the pump output pressure exceeds the load sensing valve pressure preset value, the pump only to the circuit to provide the working flow, and excess flow through the valve 2 bypass valve back to the tank.

Compared with the plunger pump, the gear pump with load sensing element has the advantages of low cost, strong anti-pollution ability and low maintenance requirements.

Priority flow control

Regardless of the speed of the pump, the working pressure or the amount of flow required by the branch, the value of the primary flow control valve always ensures the flow required for the operation of the equipment. In this circuit shown in Figure 7, the output flow of the pump must be greater than or equal to the required flow rate of the primary circuit. The secondary flow rate can be used for it or returned to the tank. Setting a flow valve (proportional valve) will be a combination of control and hydraulic pump, eliminating pipelines and eliminate external leakage, so reduce the cost. A typical application for such a gear pump circuit is the steering mechanism often found on truck cranes, which eliminates the need for a pump.

Load sensing flow control valve function and set a value of flow control function is very similar: no matter the pump speed, working pressure or branch pumping demand flow size, provide a flow. But through a port to the first oil flow to provide the required flow until its maximum adjustment value. This circuit replaces the standard primary flow control loop for maximum output flow. Due to no-load circuit pressure is lower than the value of a flow control program, so the loop temperature low, no load power consumption. Load sensing than the flow control valve, the typical application of power steering.

Bypass flow control

For bypass flow control, the pump always supplies fluid to the system at a predetermined maximum, regardless of pump speed or operating pressure, and the excess is drained to the tank or pump inlet. This scenario limits the amount of traffic that enters the system to give it the best performance. This has the advantage of controlling the maximum flow rate through the loop size to reduce costs; combining the pump and the valve and bypassing the pump to minimize loop pressure, thereby reducing tubing and leakage.

The bypass flow control valve can be designed with a medium-duty load-sensing control valve that defines the range of working flows (operating speeds). Gear pump circuits of this type are commonly used in landfill trucks or power steering pump circuits that limit the hydraulic operation for optimum engine speed and also for stationary machinery.

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