The spool shifts toward the compensator spring chamber, directing the pump’s output fluid to the stroking piston while reducing pump displacement. The compensator spool returns to a neutral position when the pump pressure aligns with the compensator spring setting. If a load obstructs the actuators, the pump flow drops to zero.
Utilizing a Automotive Lift Repair Orlando variable-displacement, pressure-compensated pump instead of a fixed-displacement pump significantly lowers circuit horsepower requirements. The output flow of this pump type adjusts according to a predetermined discharge pressure, which is detected by an orifice within the pump’s compensator.
The compensator operates from pressurized fluid, necessitating that the discharge pressure is set higher—approximately 200 psi more than the maximum load pressure setting. For example, if the load pressure setting is 1,100 psi, the pump will modulate its displacement based on a 1,300-psi discharge pressure.
In a two-stage Automotive Lift Repair Orlando pressure-compensator control, pilot flow at load pressure passes through an orifice in the main stage compensator spool, creating a 300 psi pressure drop. This drop generates a force on the spool that opposes the main spool spring. The pilot fluid is directed to the tank via a small relief valve, and a spring chamber pressure of 4,700 psi establishes a compensator control setting of 5,000 psi.
When the pressure exceeds the compensator setting, the main stage spool shifts to the right, directing the pump output fluid to the stroking piston. This action overcomes the bias piston force, reducing pump displacement to meet load demands.
The misconception mentioned earlier arises from observing that the output pressure from a pressure-compensated pump can drop below the compensator setting during actuator movement. This occurs not because the Automotive Lift Repair Orlando pump is sensing the load, but due to the pump being undersized for the application. Pressure decreases when the pump cannot produce sufficient flow to match the load. When appropriately sized, a pressure-compensated pump should always deliver enough fluid through the compensator orifice to function properly.
The two-stage compensator performs similarly to a proportional compensator control; however, its dynamic performance is notably superior. This becomes evident in scenarios involving a sudden decrease in load flow demand while starting from a full stroke at low pressure.
The single-stage control spool directs pressure fluid to the stroke piston only once the pump discharge pressure meets the compensator setting. In contrast, the main-stage spool of the two-stage control begins moving as soon as the pump discharge pressure, minus spring chamber pressure, exceeds the 300 psi spring setting. Due to the pilot fluid flowing through the orifice and the flow needed to compress the fluid in the spring chamber, the spring chamber pressure lags behind the pump discharge pressure, causing the spool to become unbalanced and shift to the right.
Pump destroking initiates before the Automotive Lift Repair Orlando pump discharge pressure reaches the compensator setting. In systems equipped with an accumulator, the two-stage compensator control offers minimal advantages. However, in excavator hydraulic systems, the superiority of the two-stage compensator is apparent, as it provides enhanced protection for system components against pressure transients.
A similar, recently popularized control is the load-sensing control, also known as power matching control. This single-stage valve resembles the single-stage compensator control, with the distinction that the spring chamber connects downstream of a variable orifice rather than directly to the tank. The load-sensing compensator spool reaches equilibrium when the pressure drop across the variable orifice matches the 300 psi spring setting.
In unloaded mode, the absence of Automotive Lift Repair Orlando load pressure prompts the pump to produce zero discharge flow at bias or unload pressure. In working mode, the load pressure causes the pump to generate discharge flow based on a set pressure drop or bias pressure. When the system achieves maximum pressure, the pump maintains this pressure by adjusting its discharge flow.
Similar to pressure-compensated pumps, load-sensing pumps feature pressure-compensation control, but with modifications to accept two pressure signals instead of one. Like pressure compensation, the load-sensing control receives a signal representing discharge pressure, along with a second signal indicating load pressure. This second signal originates from a second orifice located downstream from the first, which could be a flow-control valve immediately following the pump outlet, the spool opening of a directional control valve, or a restriction in a fluid conductor.
By comparing these two Automotive Lift Repair Orlando pressure signals in the modified compensator section, the pump can detect both load and flow, further reducing power losses. The output flow of the pump adjusts in relation to the differential pressure of the two orifices. Just as the pressure-compensated pump increases its discharge pressure to accommodate the pressure compensator, the load- and flow-sensing pump’s discharge pressure typically remains between 200 and 250 psi higher than the actual load pressure.
Moreover, a load-sensing pump can adapt to the load and flow requirements of single circuit functions or multiple simultaneous functions, correlating horsepower with maximum load pressure. This minimizes horsepower consumption and reduces heat generation.
If the variable orifice is a manually operated Automotive Lift Repair Orlando flow control valve, the system can function in a load-matched mode under operator direction. As the operator opens the flow control valve, flow increases proportionally, maintaining a constant pressure drop across the enlarging orifice, slightly above load pressure.
With a load-sensing variable volume pump compensator, power wastage is minimal. Since the control detects pressure drop rather than absolute pressure, a relief valve or another pressure-limiting mechanism is necessary.
This issue is addressed by a load-sensing/pressure-limiting control. This control operates similarly to the previously described load-sensing control until the load pressure reaches the pressure limiter setting. At that point, the limiter aspect of the compensator takes precedence over the load-sensing control to reduce pump output, while the prime mover must possess corner horsepower capability.
Load-sensing gear pumps utilize their variable-displacement feature to achieve load sensing. Unlike variable-displacement designs, standard gear pumps are less costly when compared to other options with similar flow and pressure capabilities.
A load-sensing gear pump can:
– Deliver high efficiency in load sensing without the elevated costs linked to piston or vane pumps.
– Achieve zero to full output flow in under 40 milliseconds with minimal or no pressure spikes, without requiring pump inlet supercharging.
– Operate circuits with low (approaching atmospheric) unload relief pressures.