Direct Acting vs. Pilot Operated Solenoid Valve

The solenoid valve is one of the products for fluid control automation. According to the start-up working model of the solenoid valve, it can be divided into the most frequently-used two types: pilot-operated solenoid valve and direct acting solenoid valve. However, if not choose the right one, it easily causes the solenoid valve does not work. Meanwhile, it will somewhat affect the safety of the application. Then, how to distinguish the difference between pilot-operated and direct acting solenoid valve? How to choose the right one for the better application? The following will give you some enlightenment.

Direct acting solenoid valve

The direct acting solenoid valve is usually used in small caliber and low pressure environment. For this kind of structure, when the valve is open, it will be able to start in zero pressure, without need of the minimum pressure of the medium. Therefore, it is faster in terms of the start-up speed compared with the pilot-operated solenoid valve. Thus, it is particularly suitable for the occasion in need of fast connection and disconnection.

The power consumption of direct acting solenoid valve is higher than that of the pilot-operated solenoid valve, usually ranging from 5W to 20W. Under the high-frequency power supplying, it is easy to make the coil burnt out. But, it is simple to control and has a wide application scope. It can work normally in the conditions of vacuum, negative pressure and zero pressure. Nevertheless, its diameter doesn’t exceed 25mm.

Pilot-operated solenoid valve

The pilot-operated solenoid valve is usually used in big diameter and high pressure occasions. As the valve is open, the minimum pressure of the solenoid valve is not allowed to be lower than 0.05MPa. So, the pilot pressure is required, otherwise it cannot be opened. In addition, the flow capability of the pilot-operated solenoid valve is bigger than that of the direct acting solenoid valve. It has a relatively higher requirement to the purity of the compressed air. Instead, the directly operated solenoid valve has no such high requirement.

For the pilot operated solenoid valve, the electromagnetic head is small and the power consumption is low, usually 0.1-0.2W. It can be energized frequently or for a long time, without getting burnt. It is also energy saving. As for the fluid pressure scope, it has a high upper bound. It can be installed randomly (need to be customized), but the requirement for differential pressure condition of the fluid should be satisfied. For the impurities in the liquid is easy to block the pilot valve holes. Therefore, it is unsuitable for the liquid.

Differences between pilot-operated and direct acting solenoid valve

• Pressure tolerance
  The pilot-operated solenoid valve has a higher tolerance of liquid pressure than the direct acting solenoid valve.
• Response time
  The starting speed of the direct acting solenoid valve is quicker than that of the directly operated type. It is mostly used for the occasion of fast connection and disconnection. Because the small valve opens in the first and the main valve opens later when the pilot-operated solenoid valve is supplied with power. Instead, the directly operated solenoid valve is opened with its main valve directly. When the pilot-operated solenoid valve is energized, the small valve opens at the first and the main valve opens later. However, as to the direct acting solenoid valve, the main solenoid opens directly.
• Flow capacity
  The flow capacity of the pilot-operated solenoid valve is bigger than that of the directly operated type. Generally, the CV value can reach 3 or above. However, the directly operated solenoid valve usually has the CV value of below 1.
• Power and consumption
  The power and consumption of the directly operated solenoid valve are higher than that of the pilot-operated type.
• Purity of the medium
  The pilot-operated solenoid valve has a relatively high requirement to the purity of the flowing medium. However, the direct acting type has no such strict requirement.

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