The difference between Italian ATOS proportional valves and servo valves

Brand

ATOS/Italian Atos

ATOS proportional valves control flow in two ways:

One is on/off control: either fully open or fully closed, the flow is either at its maximum or minimum, with no intermediate state, such as ordinary solenoid direct-flow valves, solenoid directional valves, and electro-hydraulic directional valves.

The other is continuous control: the valve port can open 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 throttling control of flow rate electronically (of course, pressure control can also be achieved through structural modifications). Since it is throttling control, there is inevitably 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.

Differences between ATOS proportional valves and servo valves

ATOS proportional valves are mainly distinguished by the following points:

1. Different drive devices. 1. **Differences in Driving Mechanisms:** Proportional valves are driven by proportional electromagnets; servo valves are driven by force motors or torque motors.

2. **Differences in Performance Parameters:** Hysteresis, dead zone, bandwidth, and filtration accuracy differ, leading to different applications. Servo valves and servo-proportional valves are primarily used in closed-loop control systems, while other types of proportional valves are mainly used in open-loop control systems and closed-loop speed control systems.

2.1 Servo valves have no dead zone at mid-position, while proportional valves do.

2.2 Servo valves have a higher frequency response, reaching up to approximately 200Hz, while proportional valves typically have a maximum frequency of tens of Hz.

2.3 Servo valves have higher requirements for hydraulic fluid, requiring fine filtration to prevent clogging, while proportional valves have lower requirements.

3. **Differences in Valve Core Structure and Machining Precision:** Proportional valves use a valve core + valve body structure, with the valve body also serving as the valve sleeve. Servo valves and servo-proportional valves use a valve core + valve sleeve structure.

4. **Differences in Mid-Position Functions:** Proportional directional valves have a neutral position function similar to ordinary directional valves, while servo valves only have an O-type neutral position function (E-type for Rexroth products).

5. The rated pressure drop of the valves differs.

Advantages and disadvantages of ATOS proportional valves:

Spool valve structure: The main valve of a servo valve is generally a spool valve structure, similar to that of a directional valve. However, the valve core 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 of an electro-hydraulic directional valve is an electromagnetic directional valve, while the pilot valve of a servo valve is a nozzle-flapper 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, and the pressure of the pilot valve comes from the inlet p of the servo valve. If the pressure at p is insufficient, the pilot valve cannot output enough pressure to drive 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 proportional valves actually have many disadvantages: high energy consumption, prone to failure, poor resistance to contamination, 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-overlap, while proportional valves have a certain dead zone, resulting in lower control accuracy 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 proportional valves and servo valves is not strictly defined. 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 valve spot list

DKZOR-A-171-D5 40

DKZOR-A-171-L5

DKZOR-A-171-S5

DKZOR-A-171-S5/18

DKZOR-A-173-D5

DKZOR-A-173-L5

DKZOR-A-173-L5/18 40

DKZOR-A-173-L5/Y

DKZOR-A-173-S3

DKZOR-A-173-S5

DKZOR-A-173-S5/18

DKZOR-AE-171-L5 10

DKZOR-AE-171-S5

DKZOR-AE-171-S5 10/WG

DKZOR-AE-171-S5/Y 10

DKZOR-AE-173-D5 10

DKZOR-AE-173-L5 10

DKZORC-A-151-S5/18

DKZOR-T-151-L5

DKZOR-T-151-L5/Y

DKZOR-T-153-L5

DKZOR-T-171-D5

DKZOR-T-171-L5

DKZOR-T-171-S5

DKZOR-T-171-S5/Y

DKZOR-T-173-L5 40

DKZOR-TE-170-L5 40

DKZOR-TE-171-L5

DKZOR-TE-171-L5/I 40

DKZOR-TE-171-S5 DKZOR-TE-171-S5/Y

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