I have been working in the dispensing industry for over twenty years and have experience with various types of valves. Each valve type has its suitable applications, but in processes requiring high viscosity and consistent dispensing, screw valves have proven to be a reliable choice. Based on my experience, I would like to share some insights on screw valves.

The principle of a screw valve is straightforward. A motor drives a precision screw to push out adhesive like a small screw pump. Each rotation dispenses a fixed volume, so the dispensing amount can be linearly controlled by the motor speed. Compared to time-pressure valves, this method is much more stable and not affected by fluctuations in air pressure. Unlike needle valves, screw valves do not have a significant “suck-back” effect; they rely on the screw stopping and the gap sealing to prevent excess adhesive from flowing. If stronger retraction is needed, a small reverse rotation can be programmed, which is a common adjustment technique.

Although the structure of a screw valve is not complex, it requires high precision. It consists of a motor, screw, valve body, and nozzle. The motor needs to be stable; the screw pitch affects the dispensing volume and must be selected according to the adhesive characteristics; the valve body must be precisely machined to avoid leakage or jamming; and the nozzle, usually 0.1 to 0.6 mm, controls the size of the dispensed dots. I have seen low-cost valves with poorly controlled screw-to-body gaps, and they quickly develop unstable dispensing, which is a common issue in real-world use.

Screw valves are particularly suitable for high-viscosity adhesives such as silver paste, solder paste, epoxy, and conductive glue. I have used them in LED potting processes where the adhesive volume deviation had to be within ±5%, and the screw valve performed reliably. In another case involving camera module assembly, the customer initially used a time-pressure valve, resulting in poor yield. After switching to a screw valve with a 0.2 mm nozzle, the dispensing consistency improved significantly, and yield increased by over 15%. Cases like these reinforce my confidence in screw valves.

Of course, there are limitations. Large adhesive particles can clog the screw, so filtering is necessary before use; the screw may wear over time and must be replaced periodically; and air in the supply system can cause intermittent dispensing, requiring vacuum degassing. Many on-site problems are not due to the valve itself but to insufficient support systems.

In recent years, manufacturers have made improvements, such as integrating servo motors with the valve body to enhance response speed, or adding heating to facilitate the dispensing of high-viscosity adhesives. With the development of Mini LED, semiconductor, and new energy electronics, the application of screw valves is expected to grow further.

From my perspective as a technician with over twenty years of hands-on experience, the effectiveness of a screw valve depends not only on its specifications but also on adhesive properties and process requirements. Correct valve selection, combined with proper adjustment and maintenance, is essential to ensure stable and reliable dispensing processes.