Having worked in the dispensing industry for over twenty years, I have experience with almost every type of valve. Needle valves are among the most common and basic dispensing valves. Despite their simple structure, they remain highly practical in the right applications.
The operating principle of a needle valve is straightforward: the needle moves up and down to control the flow of adhesive. When the needle presses against the valve seat, the adhesive is sealed; when lifted, adhesive flows out under air pressure or gravity. Its advantages include fast response and intuitive operation, especially suited for low- to medium-viscosity adhesives such as instant glue, UV glue, or diluted epoxy. In these applications, needle valves provide relatively stable dispensing and are easy to maintain.
A key feature of needle valves is retraction capability. When the needle closes, it creates a slight negative pressure that pulls back excess adhesive from the nozzle. This is particularly useful for low-viscosity adhesives, preventing stringing or dripping. I recall a project involving notebook speaker assembly: the client used a time-pressure valve and often experienced adhesive stringing at the nozzle, resulting in low yield. Switching to a needle valve solved the problem, thanks to the retraction function, resulting in clean and precise glue dots.
However, needle valves have limitations. First, they require adhesives within a certain viscosity range—high-viscosity adhesives can cause sticking or nozzle blockage. Second, their dispensing consistency is lower than that of screw valves, making them less suitable for high-precision applications. Needle and valve seat wear over time can also reduce sealing performance, causing dripping or incomplete shut-off, so regular replacement of wear parts is necessary.
Structurally, needle valves consist of a drive mechanism, needle, valve seat, and nozzle. They are usually air-driven, with a few electric models available. Needles are typically made of carbide or stainless steel for wear resistance. Nozzle diameters range from 0.1 to 0.5 mm, directly affecting dispensing volume. Proper pressure adjustment is essential: too high causes splashing, too low may prevent full shut-off—common considerations during on-site setup.
Needle valves are ideal for applications where adhesive volume consistency is moderate but clean dispensing is required, such as instant glue dotting, UV glue positioning, or small-area bonding in consumer electronics. Their advantages include simplicity, low cost, and compatibility with most low-viscosity adhesives.
Recently, manufacturers have improved needle valves by adding heating modules for slightly higher-viscosity adhesives or optimizing needle shapes to reduce wear and enhance retraction. While the basic principle has remained unchanged for decades, these enhancements expand their usefulness in modern dispensing processes.
In summary, needle valves, though simple in design, remain indispensable in dispensing applications. As a field technician with over twenty years of experience, I always advise clients: when selecting a needle valve, focus not on ultra-high precision but on compatibility with adhesive properties and process requirements. In suitable applications, needle valves continue to provide stable and reliable dispensing performance.