Brand

ATOS

Advantages and Disadvantages of ATOS Proportional Directional Valves

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ATOS servo valves generally have a spool valve structure, similar to directional valves. However, the valve core’s directional movement is not driven by an electromagnet, but by the hydraulic pressure output from the pilot valve. This is similar to electro-hydraulic directional valves, except that the pilot valve in an electro-hydraulic directional valve is an electromagnetic valve, while the pilot valve in a servo valve is a nozzle-flange valve or jet valve with better dynamic characteristics.

In other words, the main valve of a servo valve is controlled by the output pressure of the pilot valve, which comes from the servo valve’s inlet port (p). If the pressure at port p is insufficient, the pilot valve cannot output enough pressure to actuate the main valve core.

We know that when the load is zero, if the four-way spool valve is open, the pressure at port p = pressure at port t + pressure loss at the valve port (ignoring other pressure losses in the oil circuit). If the pressure loss at the valve port is very small, and the pressure at port t is zero, then the pressure at port p is insufficient to supply the pilot valve to actuate the main valve spool, and the entire servo valve will fail. Therefore, the valve port of the servo valve is made relatively small, so that even when the valve port is fully open, there must be a certain pressure loss to maintain the normal operation of the pilot valve.

ATOS servo valves actually have many disadvantages: high energy consumption, prone to failure, poor contamination resistance, high price, etc. Their only advantage is that their dynamic performance is the highest among all hydraulic valves. Because of this single advantage, servo valves are necessary in many applications with high dynamic performance requirements, such as aircraft and rocket servo control, and turbine speed regulation. For applications with lower dynamic requirements, proportional valves are generally preferred.

Generally speaking, servo systems seem to be closed-loop control, while proportional valves are mostly used for open-loop control. Secondly, proportional valves have more types, including proportional pressure and flow control valves, and their control is more flexible than that of servo valves. From their internal structure, servo valves are mostly zero-coverage, while proportional valves have a certain dead zone, resulting in lower control precision and slower response. However, looking at development trends, especially in proportional directional flow control valves and servo valves, the performance difference between the two is gradually narrowing. Furthermore, proportional valves are significantly cheaper than servo valves and have stronger resistance to contamination.

The difference between ATOS servo valves and proportional valves: There is no strict definition of the difference between servo valves and proportional valves. Because the performance of proportional valves is constantly improving and gradually approaching that of servo valves, proportional servo valves have emerged in recent years.

ATOS proportional directional valves can control flow in two ways: one is on/off control: either fully open or fully closed, with the flow rate either at its maximum or minimum, without intermediate states, such as ordinary solenoid straight-through valves, solenoid directional valves, and electro-hydraulic directional valves. The other is continuous control: the valve port can be opened to any degree as needed, thereby controlling the flow rate. These valves can be manually controlled, such as throttle valves, or electrically controlled, such as proportional valves and servo valves. Therefore, the purpose of using proportional valves or servo valves is to achieve flow throttling control electronically (of course, pressure control can also be achieved through structural modifications). Since it’s throttling control, there will inevitably be energy loss. Servo valves differ from other valves in that their energy loss is greater because they require a certain flow rate to maintain the operation of the pre-stage control circuit.

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