Having worked in the dispensing industry for over 20 years, I have experienced the evolution from early pneumatic valves to today’s high-precision designs. Each valve type has its unique advantages, limitations, and application scenarios. Based on my hands-on experience, I would like to share my insights into screw valves, needle valves, and jet valves, as well as key considerations when applying them in production.

At the core of a screw valve is a precision screw driven by a motor, which dispenses adhesive like a miniature screw pump. Each rotation corresponds to a fixed volume, allowing the output to be linearly controlled by motor speed. Unlike time-pressure valves, screw valves are unaffected by air source fluctuations and offer much greater stability.
One limitation is that screw valves have little natural suck-back. In practice, I often set a small reverse angle in the program to simulate suck-back and reduce tailing.
Screw valves consist of a motor, screw, valve body, and nozzle. High-precision applications require screw-to-barrel clearance within 10 microns to ensure long-term stability. They are particularly suitable for high-viscosity adhesives such as silver paste, solder paste, epoxy, and conductive adhesives. In LED encapsulation and semiconductor packaging, screw valves can control dispensing variation within ±5%, ensuring consistent production quality.

Needle valves rely on the up-and-down motion of a needle. When pressed against the seat, it seals; when lifted, adhesive flows out under pressure or gravity. With fast response and good suck-back, needle valves are ideal for low-viscosity fluids to prevent dripping or stringing.
In one notebook speaker assembly project, a customer had poor yields with a time-pressure valve due to adhesive stringing at the nozzle. Switching to a needle valve solved the issue—the suck-back kept dots neat and clean. However, needle valves are not suitable for high-viscosity adhesives, offer less stable volume control than screw valves, and require frequent maintenance as needle-seat wear affects sealing.

Jet valves dispense adhesive by ejecting micro-droplets through high-frequency needle or diaphragm motion. They offer millisecond response speeds and are ideal for micro-dispensing at high speed.
In applications like Mini LED encapsulation, camera modules, and micro-electronics, jet valves deliver extremely small, precise deposits without contact. However, they demand strict adhesive properties—any particles or high viscosity can cause clogging, making filtration and degassing essential. Jet valves also lack mechanical suck-back, so tail control depends on fast needle actuation and software settings. While costly and maintenance-intensive, they are irreplaceable in high-speed, high-precision micro-dispensing scenarios.

From my projects, screw valves ensured stable dispensing with high-viscosity adhesives, improving yields by 10–15%. Needle valves excelled in precise dotting with low-viscosity adhesives. Jet valves, although expensive, proved indispensable for micro, high-speed applications.

Selecting a dispensing valve is not just about comparing specifications but about matching adhesive properties, process requirements, and production goals. From my two decades of frontline experience, I have learned that equipment performance matters, but process optimization, tuning, and regular maintenance are equally critical. Screw, needle, and jet valves each have their strengths—understanding their principles and best-fit scenarios is the key to maximizing value in dispensing production.