8. Direction control valves Direct operated, pilot operated

Direction control valves: Direct operated, pilot operated {Hydraulics} Making India Employable

Directional control valves Directional control valves perform only three functions: • stop fluid flow • allow fluid flow, and • change direction of fluid flow. These three functions usually operate in combination. Classification of Directional Control Valves: Directional control valves can be classified according to- • number of ports • number of positions • actuating methods • type of spool For internal Training purposes only

Direct acting solenoid valve Pilot-operated solenoid valve • The direct acting solenoid valve is • The pilot-operated solenoid valve is usually usually used in small caliber and low used in big diameter and high pressure pressure environment. For this kind of occasions. As the valve is open, the structure, when the valve is open, it minimum pressure of the solenoid valve is will be able to start in zero pressure, not allowed to be lower than 0.05MPa. So, without need of the minimum pressure the pilot pressure is required, otherwise it of the medium. Therefore, it is faster in cannot be opened. In addition, the flow terms of the start-up speed compared capability of the pilot-operated solenoid with the pilot-operated solenoid valve. valve is bigger than that of the direct acting Thus, it is particularly suitable for the solenoid valve. It has a relatively higher occasion in need of fast connection and requirement to the purity of the compressed disconnection. air. Instead, the directly operated solenoid valve has no such high requirement.

Differences Between Direct & Pilot-Operated Regulating Valves Regulators, both pressure and temperature, can be classified as either “direct” or “pilot” operated depending on their design characteristics. The purpose of this primer is simply to explain the differences between these two types and highlight the benefits of each for proper selection per application. Below is a simple comparison highlighting the basic variations and characteristics of direct and pilot-operated regulators. • Pressure tolerance: The pilot-operated solenoid valve has a higher tolerance of liquid pressure than the direct acting solenoid valve. For internal Training purposes only



• 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. For internal Training purposes only



• 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. For internal Training purposes only

https://www.youtube.com/watch?v=vfz_CM0ygs4 Pressure Relief Valves: Direct Acting and Pilot Operated

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