DR Type Constant Pressure Variable Control
Introduction to Constant Pressure Variable Pumps
Pumps with constant pressure variable mechanisms belong to the category of pressure regulating pumps, and are usually referred to as constant pressure pumps. Since the control oil that actuates the constant pressure valve comes from the outlet of the variable pump itself, it is classified as a self-controlled (self-supplied) variable pump. This type of pump is widely used in various hydraulic systems, including those incorporating a hydraulic rotary motor, where maintaining stable pressure is crucial for optimal performance.
The constant pressure variable control of a variable pump means that when the flow rate is adaptively adjusted, the pressure change is very small, providing a constant pressure source to the system. This characteristic makes it particularly valuable in applications where consistent pressure is required regardless of flow variations, such as in precision hydraulic systems that power a hydraulic rotary motor with varying load demands.
The ability to maintain constant pressure while adjusting flow makes these pumps highly efficient, as they only deliver the necessary flow for the current demand, reducing energy waste. This efficiency is especially beneficial in systems where a hydraulic rotary motor operates under fluctuating load conditions, as it ensures the motor receives consistent pressure while the pump adjusts flow accordingly.
Working Principle of Constant Pressure Control
The principle of constant pressure control is illustrated in Figure 4-14. The constant pressure valve CP controls the oil inlet and return of the pump's variable piston, which in turn controls the swash plate angle of the pump, thereby changing the pump's displacement. This mechanism ensures that the system pressure remains stable even as flow requirements change, which is essential for applications involving a hydraulic rotary motor.
In Figure 4-14, assume that the preset pressure of the pressure regulating spring at the right end of the constant pressure valve is P, the pump's outlet flow is q, and the pump's outlet pressure is P. When p < P, the valve core of the constant pressure valve moves to the left under the action of the spring force, connecting the top of the variable piston to the oil tank. As a result, the pump's output flow reaches its maximum, i.e., q = qmax. This maximum flow capacity is particularly important when a hydraulic rotary motor needs to operate at higher speeds.
If the load flow qL < qmax, meaning the pump's output flow is greater than what the load requires, the excess flow will cause the system pressure to rise, thereby increasing the pump's outlet pressure. When P > P (since the valve core of the constant pressure valve has a very small stroke during movement, we can consider the spring force of the constant pressure valve core to always be its preset pressure value P), the spool of the CP valve moves to the right, introducing pressure oil to the top of the variable piston. This action reduces the pump's displacement, eventually stopping when q = qL, which causes the pump's outlet pressure to decrease.
Figure 4-14: Constant pressure control principle and pressure-flow characteristic curve
Therefore, when q < qmax, P = P. At this point, the constant pressure valve closes, the variable piston stops moving, the variable process ends, and the pump's working pressure stabilizes at the set value. This stability is crucial for applications such as a hydraulic rotary motor, where consistent pressure ensures predictable and reliable performance.
By adjusting the preload of the pressure regulating spring, the working pressure of the pump can be adjusted. This adjustability allows the system to be optimized for different operating conditions, whether the hydraulic rotary motor is operating under light or heavy loads. Based on this, we can obtain the pressure-flow characteristic curve of the constant pressure control, as shown in Figure 4-14b.
It can be seen that regardless of the load flow q, as long as q < qmax, the pump's outlet pressure remains basically unchanged, always maintaining the set pressure P of the constant pressure valve spring. This characteristic is what makes these pumps ideal for systems where pressure stability is paramount, including those utilizing a hydraulic rotary motor in precision applications.
Safety Considerations for DR Type Constant Pressure Pumps
When using DR type constant pressure variable pumps, any relief valve (safety valve) in the circuit that is used to limit the maximum pressure should be set to a safety pressure at least 2MPa higher than the constant pressure pump's pressure setting. This safety margin protects both the pump and other system components, including any hydraulic rotary motor connected to the system.
System Pressure Behavior
When the system pressure has not reached the constant pressure setting of the constant pressure pump, it will always supply the maximum flow to the system, effectively functioning as a fixed displacement pump. This is important to understand when sizing components like the hydraulic rotary motor, as they must handle maximum flow conditions.
Flow Adjustment Characteristics
Before the constant pressure pump enters the constant pressure operating condition, its displacement (which, multiplied by speed, gives flow) is already at maximum. Therefore, if flow adjustment is needed, the flow will only decrease. This means that when a constant pressure pump operates under constant pressure conditions, its flow can only be equal to or less than the maximum flow, which affects the performance capabilities of any hydraulic rotary motor in the system.
Speed and Flow Relationship
When the system speed decreases, meaning less flow is required, the variable mechanism of the constant pressure variable pump automatically reduces the swash plate angle to match the system's flow needs while maintaining essentially constant system pressure. This is particularly beneficial for a hydraulic rotary motor, as it allows for speed control while maintaining torque output.
Pressure Holding Phase
When the system enters a pressure-holding phase where no more flow is needed, the constant pressure pump outputs only the flow required to maintain internal leakage, no longer supplying oil to the system. This energy-saving feature is especially valuable in systems where a hydraulic rotary motor may be in a holding position for extended periods.
Proper Operating Conditions
For a constant pressure pump to work properly, in addition to the basic condition that the system pressure must reach the set value, this basic condition must also be achievable. If the relief valve in the system is set to a pressure lower than the set value of the constant pressure pump, the constant pressure pump will never be able to enter the constant pressure operating condition and will remain a fixed displacement pump with maximum displacement. This scenario can lead to inefficiencies and potential damage, especially to components like the hydraulic rotary motor that depend on proper pressure regulation.
Pressure Regulation Mechanism
The pressure oil at the outlet of the hydraulic pump acts on the left end of the valve core. As the outlet pressure of the hydraulic pump increases, the valve core moves to the right. When the outlet pressure exceeds the preset value of the spring, the valve control port opens, connecting the hydraulic pump's outlet pressure oil with the variable piston chamber. This action pushes the variable valve sleeve, placing the pump's swash plate in a "zero" swing angle position.
The pump can automatically vary its displacement according to the needs of the load flow, thereby maintaining a constant system pressure. This capability is essential for applications where a hydraulic rotary motor must maintain consistent torque output regardless of speed variations.
The pressure can be infinitely adjusted through the pressure regulating screw on the control valve. Turning it counterclockwise increases the pressure, while turning it clockwise decreases the pressure. This precise adjustability allows for fine-tuning of system performance to match the requirements of the hydraulic rotary motor and other system components.
Proper adjustment of these settings ensures that the hydraulic system operates within optimal parameters, providing the necessary pressure to the hydraulic rotary motor while maintaining efficiency and preventing damage from overpressure conditions.
The relationship between pressure settings and flow output directly impacts the performance of the entire hydraulic system. Operators must understand how these adjustments affect the hydraulic rotary motor's operation to ensure safe and efficient system performance.
Figure 4-17: Adjustment of constant pressure variable pump
- • DR valve pressure regulating screw (locked)
- • Pump outlet pressure oil
- • Pressure regulating screw
- • Return oil
- • Oil entering variable piston
Applications and Advantages
DR type constant pressure variable pumps find applications in a wide range of industrial and mobile hydraulic systems where maintaining stable pressure is critical. These include machine tools, injection molding machines, hydraulic presses, and various types of construction equipment. In many of these applications, the pump works in conjunction with a hydraulic rotary motor to convert hydraulic energy into mechanical rotational motion.
Energy Efficiency
By adjusting flow output based on demand while maintaining constant pressure, these pumps significantly reduce energy consumption compared to fixed displacement pumps. This efficiency is particularly beneficial in systems utilizing a hydraulic rotary motor for extended periods.
Stable Performance
The constant pressure output ensures consistent operation of system components, including the hydraulic rotary motor, resulting in predictable and reliable performance even under varying load conditions.
Versatility
With adjustable pressure settings, these pumps can be easily adapted to different system requirements, making them suitable for a wide range of applications where a hydraulic rotary motor may need to operate under various pressure conditions.
In systems where a hydraulic rotary motor is the primary actuator, the constant pressure characteristics of DR type pumps provide several advantages. The motor receives a consistent pressure supply, ensuring that torque output remains stable regardless of speed variations. This is particularly important in precision applications such as automated manufacturing processes, where consistent performance is essential.
Another key advantage is the pump's ability to reduce flow to a minimum during pressure-holding phases, which not only saves energy but also reduces heat generation in the system. This is beneficial for maintaining optimal operating temperatures for both the pump and the hydraulic rotary motor, extending their service life and reducing maintenance requirements.
When properly integrated into a hydraulic system with a hydraulic rotary motor, DR type constant pressure variable pumps contribute to overall system efficiency, reliability, and performance. Their ability to maintain constant pressure while adjusting flow according to demand makes them an ideal choice for many modern hydraulic applications.
The combination of a DR type constant pressure variable pump with a high-quality hydraulic rotary motor creates a powerful and efficient hydraulic system capable of handling varying loads while maintaining precise control. This makes such systems invaluable in industries ranging from manufacturing to construction, where performance, efficiency, and reliability are paramount.
Maintenance and Troubleshooting
Proper maintenance of DR type constant pressure variable pumps is essential to ensure their longevity and reliable performance, especially in systems that include a hydraulic rotary motor. Regular inspection and maintenance can prevent unexpected downtime and costly repairs.
Regular Maintenance Tasks
- Check oil levels and quality regularly to ensure proper lubrication of all components, including those in the hydraulic rotary motor.
- Inspect for leaks around the pump housing, connections, and seals, as leaks can lead to pressure loss and inefficient operation.
- Clean or replace filters according to manufacturer recommendations to prevent contamination from damaging the pump and hydraulic rotary motor.
- Check pressure settings periodically to ensure they remain within the recommended range for your specific application.
- Lubricate any external moving parts as specified in the maintenance manual to prevent excessive wear.
Common Troubleshooting Issues
- Pressure fluctuations: May indicate a worn valve core, contaminated oil, or issues with the pressure regulating spring, all of which can affect hydraulic rotary motor performance.
- Inability to reach set pressure: Could be caused by a leaking relief valve, worn pump components, or incorrect spring adjustment.
- Excessive noise or vibration: May signal worn bearings, misalignment, or cavitation, which can also impact the hydraulic rotary motor.
- Overheating: Often caused by inefficient operation, contamination, or insufficient oil flow, potentially damaging both the pump and hydraulic rotary motor.
When troubleshooting issues with a DR type constant pressure variable pump, it's important to consider the entire hydraulic system, including the hydraulic rotary motor, as problems in one component can often manifest as issues in another. Regular maintenance and prompt attention to any anomalies will help ensure the system operates efficiently and reliably for its intended service life.
Conclusion
DR type constant pressure variable control represents a sophisticated solution for hydraulic systems requiring stable pressure output with variable flow rates. These pumps offer numerous advantages, including energy efficiency, consistent performance, and adaptability to varying load conditions. When paired with a hydraulic rotary motor, they form a powerful combination capable of delivering precise control and reliable operation across a wide range of industrial applications.
Understanding the working principles, proper adjustment methods, and maintenance requirements of these pumps is essential for maximizing their performance and longevity. By following the recommended guidelines and ensuring that system components, including the hydraulic rotary motor, are properly sized and configured, operators can achieve optimal system performance and efficiency.
As hydraulic technology continues to evolve, DR type constant pressure variable pumps remain a cornerstone of modern hydraulic systems, providing the reliability and efficiency needed in today's industrial environment. Their ability to maintain constant pressure while adjusting flow according to demand makes them an indispensable component in systems utilizing a hydraulic rotary motor for precision applications.