Pressure Based Precision Fluid Dispensing
Many industrial processes require fluid dispensing systems to apply any number of fluids to the part or process. One method of dispensing fluid is with a pressurized fluid dispenser system. Such a system uses a pressurized fluid source to push the fluid through tubing to either drip, spray, or coat an object. Maximum impact spray nozzles are often used in this type of application to distribute the fluid to the target.
How does pressure based precision fluid dispensing work?
Obtaining the correct pressure and amount of fluid dispensed is possible with the right systems in place.
How is the system pressurized and how is that pressure controlled?
Pressure based fluid dispensing starts by pressurizing the fluid to dispense. This can be done with an air over fluid pressure tank (air pressure reservoir) that uses compressed air to drive the fluid, or it can be done with a type of pump such as a diaphragm pump or rotary vane pump with pressure relief.
How is the rate or volume of fluid dispensed precisely?
The pressurized fluid is typically metered through a valve or orifice. Fluid metering is achieved with a high pressure spray nozzle tip with a defined orifice size, a manual needle valve to control the flow of the fluid, or with a discrete on/off solenoid valve where the duration of time that the valve is open controls the volume of fluid dispensed. More sophisticated systems use an electronic air pressure regulator or a proportional solenoid valve to meter the flow of fluid to the application zone.
What are all the elements to a pressure based precision dispensing system?
Pressure based dispensers always require some means of generating the fluid pressure, means of controlling the flow rate, and then the high pressure sprayer nozzle or other applicator to deliver the fluid to the final target. Fluid can be drawn from a pressure tank or another reservoir depending on the delivery set up. For intelligent control, a fluid flow meter must be incorporated as the actual flow rate can not be known even if the pressure and orifice restriction sizes are known. This type of system is sensitive to changes in viscosity, contamination build up, or other ambient conditions as these will all affect the flow rate of the system. Therefore if a precise flow rate or volume is to be delivered with a pressure based dispensing system, a closed loop control must be used.
What are the benefits of pressure based dispensing over other methods?
At their most basic level of implementation, pressure based dispensing systems are inexpensive. A small pressure tank, needle valve, and manual on off valve feeding a precision spray nozzle is an economical way to deliver fluid. These are however not very accurate and are sensitive to small changes in valve orifice, inlet pressure, and fluid viscosity changes. For thin fluids with a low viscosity index such as water-based fluids, they may provide satisfactory results.
Pressure based dispensers will provide smooth, pulse free flow, if that is a requirement, and are capable of a maximum impact spray with the right supply for high pressure spray applications. With a closed loop control of delivery pressure, orifice size, and a fluid flow meter an accurate system can be designed.
What are the downsides or challenges compared to other methods?
The downsides of pressure driven dispensing solutions is the volumetric accuracy. Frequent calibrations are required to keep an open loop pressure based dispensing control system accurate. It is difficult to calculate the flow rate from a high pressure spray nozzle without a flow meter. Otherwise a closed loop control is required and this can be expensive. Clogging, pressure changes, and viscosity changes all will affect the amount of material dispensed. If your process has a wide tolerance in the amount of fluid applied, pressure-based dispensing is a good option.
Unist products for pressure based systems
Unist offers several pressure based dispensing solutions ranging from air over fluid pressure supply tanks, metering block dispensers, and solenoid valve controlled dispensing with electronic programmable fluid controllers. We also can help design a closed loop control system for your dispensing needs. Contact us today to help you select the best pressure nozzle for your precision based fluid dispensing system.