The ability to move these liquids repeatedly, and reproducibly, is essential to creating successful liquid handling systems.
Time-metered dosing, uses air to pressurise a reservoir, and a fast-acting valve to control the quantities of a liquid being dispensed precisely.
By combining the high level of pressure control provided by the disc pumps, and the ultra-fast and consistent operation of The Lee Company VHS valves, we have built a prototype of a compact (100x90x20mm), low-weight (<50g) time-metered dosing system as a proof of concept, outlined in the AN059: Time-metered dosing – Disc Pump Application Note.
The application note outlines the following:
• The basic design and operation of a time-metered dosing system
• Priming and operating the time-metered dosing system
• Data from a prototype system
• In-situ set up of the system
For a quick summary of the basics and key takeaways please see below.
A disc pump, mounted as a Smart Pump Module
The disc pump’s fast response and pulsation-free output allow for a high level of pressure control. The disc pump can very accurately hold a target pressure above the fluids, the dispensed volume is then controlled by the accurate head pressure and opening and closing of the VHS valve for a defined length of time.
Using the disc pump mounted as a Smart Pump Module enables closed-loop pressure control, and the speed of response ensures that the desired pressure/flow profiles are followed accurately/the integrated drive electronics allow all components of the module to be controlled remotely with software is provided for free on The Lee Company's website.
VHS series 2-Way Dispense Solenoid Valve
The VHS Series 2-Way Dispense Solenoid Valve is a 2-way, 6mm dispensing valve that combines inkjet printing technology with inert materials to achieve precision droplets in the nanolitre to millilitre range.
With an ultra-fast response time (as fast as 250µs), it is ideal for accurate fluid regulation and dispensing repeatable droplets with minimal satellites.
The valve’s small size enables mounting in tight spaces, even in arrays directly above a well plate. It is offered with integrated precision orifices, nozzles, screens, or with our MINSTAC connectors to vary the outlet nozzle and connect tubing.
Results
The graph to the right shows the average water droplet mass achieved for a range of reservoir pressures (Pr) and valve on-times (td). As the droplets are small (~ uL), measurements reported are based on the average droplet mass as measured using a 3-decimal place mass balance.
“A coefficient of variance (CV) of ~ four percent was demonstrated at dose sizes of 10mg (10uL), and at smaller dose sizes this value is believed to be limited by the resolution of the mass balance used in this demonstration.”
Key takeaways
Exciting opportunities lie ahead as we explore a wider dosing range with better instrumentation – we are actively involved in projects using droplet analysers to produce future literature and guidance on this topic. We are looking to characterise the dispensing precision of dosing sizes smaller than 10uL by eliminating current measurement limitation.
The compact nature of the system (100x90x20 mm) will prove a huge asset when miniaturising and commercialising systems – improving not only the end-user experience, but also the time to market and commercial viability of a system.
New, lightweight (<50g) pressure-driven systems such as this can unlock a new generation of untethered, automated, tightly integrated liquid handling devices. Current benchtop equipment for pressure-driven flow systems often needs separate pumps, pressure regulators and sensors and can be very heavy and bulky, weighing several kilograms.
For further information on system set-up and results, please see AN059: Time Metered Dosing – Disc Pump Application Note.