Gear pumps are typically regarded as constant-flow hydraulic sources due to their fixed displacement design. However, the integration of an attachment-threaded coupling valve significantly enhances their functionality, reduces system costs, and improves reliability. This makes gear pumps more versatile and capable of performing tasks previously reserved for complex and expensive piston pumps.
One effective approach is to directly mount the control valve on the pump, eliminating the need for additional piping between the pump and the directional control valve. This not only cuts down on installation costs but also minimizes the number of fittings and connections, reducing potential leakage points and improving overall system reliability. Additionally, integrating the valve with the pump helps lower the circuit’s pressure cycle, thereby enhancing performance.
Several circuits can be used to expand the basic functions of a gear pump. Some are well-established, while others represent innovative solutions. For example, unloading circuits allow high-flow and low-power pumps to work together. When the system reaches a set pressure or flow rate, the high-flow pump redirects its output back to the inlet, reducing the overall flow supplied to the system. This process is controlled by an unloader valve, which can be manually, hydraulically, or electronically operated. Manual valves are often used in applications requiring rapid response, such as telescopic boom systems, while electronic controls offer automated operation and greater precision.
Pressure-sensing unloading valves are another common solution. These valves use a spring to keep the pump in a high-flow position until a preset pressure is reached, at which point the valve shifts to a low-flow mode. This is particularly useful in applications like hydraulic jacks or splitters, where precise pressure control is essential.
Flow-sensing unloading circuits adjust based on engine speed. If the engine exceeds its optimal range, the flow through a fixed orifice increases, causing the unloader valve to shift and reduce the flow. This helps maintain efficient operation and reduces energy consumption, making it ideal for vehicles like garbage trucks.
In load-sensing systems, two pumps work in tandem, each responding to signals from the other. This allows one pump to operate at high pressure while the other provides high flow, optimizing performance and reducing power demands. Such systems are commonly found in mining equipment where variable loads and speeds are typical.
Priority flow control circuits ensure that the primary system receives the required flow regardless of pump speed or pressure. Excess flow can be redirected back to the tank, minimizing waste and reducing costs. These circuits are widely used in truck cranes and similar applications where consistent performance is crucial.
Bypass flow control systems regulate maximum flow by diverting excess fluid to the tank or pump inlet. This ensures stable system performance and reduces wear on components. These circuits are often used in power steering systems and stationary machinery.
Dry suction valves are another innovative feature. They prevent excessive flow when the system is under low load, reducing no-load power consumption and noise. This is especially beneficial in vehicles powered by internal combustion engines, such as refuse trucks.
Today, gear pumps are capable of handling pressures close to those of piston pumps, and with advanced load-sensing schemes, they can even offer variable flow capabilities. As a result, the traditional distinction between gear and piston pumps is becoming less clear. When choosing a hydraulic pump, cost, simplicity, and maintenance requirements play a significant role. Gear pumps remain a practical and cost-effective option in many applications, offering reliable performance without the complexity of piston pumps.
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