Taking a low viscosity material (100 CPS) that can be quickly cured as an example, such as cyanoacrylate adhesive, this type of fluid is likely to require adhesive release, which means that the adhesive valve used for adhesive application must be able to prevent the fluid from blocking the channel due to curing during the adhesive application cycle. At the same time, the rubber valve must be able to separate the moving parts driven by air from the wet parts.
For water or low viscosity fluids, the suitable rubber valve should be able to ensure that the fluid can still flow under low pressure, which is commonly referred to as gravity supply. At this time, the available rubber valves include clamping valves, needle valves, or diaphragm valves.
The viscosity of low to medium viscosity fluids is similar to that of milk fat materials. The pressurized storage container for feeding such fluids needs to have degassing and stirring functions. A plunger valve with suction function is suitable for this type of fluid. Medium viscosity fluids can also be operated by pneumatic needle valves.
For corrosive materials with high viscosity (500000cps) and abrasive fillers, high-strength pneumatic rubber valves with corrosion-resistant and wear-resistant sealing components are very suitable. The higher the grindability of the material, the more frequent the maintenance cycle of the rubber valve.
In addition to viscosity, some rheological properties of the fluid also need to be considered. Fluid with thixotropy is difficult to pour, but after stirring, it becomes creamy and easy to pour. Tomato sauce is a good example of this situation. The fluid with syrup viscosity and gel require the same requirements, but the difference is that such fluid is generally stored in a small tank that has not been degassed. Therefore, we need to consider how to extract the fluid from the tank and degas it from the point valve. The viscosity of the paste like fluid is higher and can be directly extracted from the packaged container into the glue valve. Normally, such fluids have already been degassed, but this still needs to be confirmed with the manufacturer. Pneumatic glue valves suitable for paste like fluids include plunger valves and high-pressure needle valves. If it is used for micro adhesive application of high viscosity fluids, it is recommended to use an electric screw pump.
The hardness of the fluid is also a factor that needs to be considered. For example, corrosive fluids may contain acids, bases, methanol, and solvents. These substances will react with the wet chamber, piston, and O-ring. Therefore, diaphragm valves or needle valves must be able to withstand corrosive substances, while pistons and O-rings should be made of acid resistant ultra-high molecular weight materials. Ultra high molecular weight materials can also withstand alcohol and methanol. Based on the specific corrosive strength, polyetheretherketone materials are also applicable.
Clamping valves are commonly used for acid and all solvent based materials, as their polyethylene pipes are disposable. The clamping valve has no wet chamber that can be corroded. Adhesive fluids, such as cyanoacrylate, are solvent based adhesives with strong corrosiveness. Therefore, if a diaphragm valve is used, the materials for its wet chamber, piston, and O-ring must be ultra-high molecular weight materials. Grinding fillers are usually in the form of paste, which can improve the conductivity and dielectric properties of the material. Not all fillers have abrasive properties, and the specific product properties need to be confirmed with the manufacturer or supplier. Once it is determined that the fluid has abrasive properties, a dispensing valve should be selected: the wet chamber must be made of high hardness stainless steel material; Seals must have high strength, be able to withstand continuous wear, and have the lowest possible repair rate.
