The application of solenoid valves in vacuum environments requires specialized optimization to address backflow, sealing reliability, and material adaptability. Their structural design necessitates a comprehensive consideration of interdisciplinary technologies, including fluid dynamics, materials science, and electromagnetic control. The unique characteristics of a vacuum environment lie in the rarefied medium, drastic pressure gradient changes, and the ineffectiveness of traditional gravity- or atmospheric-pressure-assisted sealing mechanisms. Therefore, a combination of active control and passive protection is necessary to achieve backflow prevention.
From a sealing structure perspective, solenoid valves require a two-stage sealing design, with a primary sealing surface and an auxiliary sealing surface working in tandem. The primary sealing surface typically uses a metal bellows or an elastomer sealing ring. The former achieves zero-leakage sealing through the expansion and contraction of the bellows, while the latter relies on the low outgassing rate of fluororubber or perfluororubber to ensure continued sealing performance even in ultra-high vacuum environments. The auxiliary sealing surface optimizes the contact angle between the valve seat and valve disc, utilizing the fluid pressure difference to create a self-sealing effect. When the medium attempts to backflow, the pressure difference forces the valve disc to fit more tightly against the valve seat, thus blocking the backflow path.
The choice of valve body material directly affects the adaptability of the solenoid valve in vacuum environments. Stainless steel is the preferred choice due to its low saturated vapor pressure, high corrosion resistance, and chemical stability, especially 316L stainless steel, which has a high molybdenum content and effectively resists chloride ion corrosion, making it suitable for vacuum systems containing corrosive media. For ultra-high vacuum environments, materials with low outgassing rates, such as oxygen-free copper or aluminum alloys, must be further used, and vacuum baking treatment should be used to remove adsorbed gas molecules from the material surface, reducing the risk of system contamination. Furthermore, the thermal expansion coefficients of the valve body and moving parts must be matched to avoid jamming or sealing failure due to temperature changes.
Optimization of the electromagnetic control system is crucial for preventing backflow. Traditional solenoid valves rely on spring reset to achieve the closing action, but in a vacuum environment, the elastic modulus of the spring may change due to low or high temperatures, resulting in insufficient closing force. Therefore, a dual-electromagnet drive structure is required, with one electromagnet responsible for the opening action and the other for the closing action, achieving precise valve disc position adjustment through independent control. In addition, a position feedback sensor is introduced to monitor the valve disc opening in real time. When abnormal opening is detected, the closing electromagnet is immediately triggered, forming an active protection mechanism.
The flow channel design has a critical impact on backflow prevention performance. The flow channel of a solenoid valve must employ a gradually expanding and contracting structure to avoid eddies or sudden pressure changes during media flow. Eddies lead to energy loss and reduce the valve's closing speed; while sudden pressure changes can trigger water hammer, causing impact damage to the valve body. Computational fluid dynamics (CFD) simulations optimize the flow channel curvature, making the media flow closer to a laminar state. This reduces energy loss and ensures the valve receives sufficient reverse pressure at the moment of closure, quickly blocking media flow.
Matching the vibration period with the spring stiffness is another crucial factor in preventing backflow. The valve core's vibration period directly affects its closing response time. If the period is too long, the media may flow backward before the valve is fully closed; if the period is too short, the valve core may frequently impact the valve seat, shortening its service life. By adjusting the spring stiffness and the valve core's equivalent mass, the vibration period is kept within a reasonable range, ensuring rapid closure while avoiding excessive vibration. Furthermore, a built-in one-way check valve serves as an auxiliary protection measure. When the main solenoid valve fails, the one-way valve automatically closes to prevent media backflow.
Solenoid valves operating in vacuum environments also require consideration of heat conduction and dissipation. Due to the lack of air convection in a vacuum, the heat generated by the solenoid coil is difficult to dissipate naturally, potentially leading to aging of the coil insulation or demagnetization of the magnetic material. Therefore, a radiative cooling design is necessary, such as adding heat sink fins or using materials with high thermal conductivity, to conduct heat to the valve body surface, and then dissipate heat through the contact between the valve body and the mounting base. For high-power solenoid valves, active cooling devices, such as miniature heat pipes or semiconductor cooling chips, can also be used to ensure the coil operating temperature remains within a safe range.
The backflow prevention design of solenoid valves in vacuum environments requires a comprehensive approach, considering factors such as sealing structure, material selection, electromagnetic control, flow channel optimization, vibration cycle matching, thermal management, and auxiliary protection. By combining active control with passive protection, reliable operation of the solenoid valve in a vacuum environment can be ensured, while effectively preventing system failures caused by media backflow, providing technical support for high-precision vacuum applications.
