The meniscus is a curved ink surface located at the tip of each inkjet printer nozzle. For DOD inject printing the meniscus must be kept stable in order to provide the essential print quality expected by users—particularly in demanding industrial printing environments. These printers provide precision and repeatable print results in markets such as digital graphics, ceramics, glass, textile printing, printing electronics, and 3D printing. 

Unlike Continuous Inkjet (CIJ) systems, which generate a continuous stream of ink droplets, DOD printers eject ink droplets only when required, making this process accurate, economical, and clean. Modern DOD systems are sophisticated environments that include pumps for ink supply, degassing, and recirculation as well as for purging applications. 

A key part of the system is the flow-through printhead, which circulates ink through arrays of micro-nozzles. This circulation helps to maintain stable temperature and pigment distribution, ensure consistent ink viscosity, improve start-up reliability, and prevent nozzle blockage. Such features help to reduce purging efforts while also enabling higher print speeds. 

Meniscus Control in DOD Printing

Each color is stored in a container positioned above the printhead. To stabilize the ink flow inside the printhead, the system maintains a pressure balance between the inlet supply pressure and the controlled negative pressure (vacuum) applied on the outlet side of the printhead — called meniscus pressure. This pressure balance compensates for hydrostatic pressure and keeps the meniscus in a stable position. 

The meniscus forms the boundary between the ink inside the nozzle and the surrounding air. Its position depends entirely on this pressure balance. If the meniscus pressure is too high, the ink cannot be held back and may flood the nozzle causing involuntary drops to drip. If the meniscus pressure is too low, the ink retracts too far into the nozzle, limiting refill performance and potentially leading to missing dots.

In conventional DOD systems, the vacuum in the printhead is created by a diaphragm vacuum pump. Its stable and reliable performance is essential, as pressure fluctuations of even 3-5 mbar can reduce print quality. For this reason, many systems monitor pressures directly at the inlet and return via pressure sensors, or indirectly via mass flow meters, to detect deviations.

Incorporating KNF’s intelligent feature, Vacuum Control, can eliminate the need for external pressure measurements and decreases DOD system complexity, which also decreases maintenance costs. With Vacuum Control, the pump automatically monitors and adjusts its performance to maintain the defined vacuum setpoint.

A meniscus pressure control pump, such as the NVC 830 HP with Vacuum Control increases precision and stability of the ink delivery process. Thanks to an integrated sensor, and control programing, the pump automatically adjusts its own performance to maintain the exact vacuum required for a stable meniscus. This creates consistent droplet formation and controlled ink droplet dispensing even when conditions fluctuate. 

The single-head version reaches an ultimate vacuum of 200 mbar and a maximum flow rate of 4.7 l/min. Customers can adjust the desired vacuum setpoint during printing. Thanks to the pumps backflow-tight design, the NVC 830 HP maintains the vacuum level even when turned off. This ensures a reliable meniscus at the printhead, which prevents leakage, drying, air ingestion, or misfires.

The dual-headed NVC 830.3, equipped with PPS pump head and EPDM diaphragms and valves (other materials are available upon request), safely handles water-based, solvent-based, pigmented, and reactive inks, even in challenging viscosity ranges. Its oil-free operation prevents contamination to ensure high print quality. This intelligent pump with Vacuum Control delivers a high pneumatic performance with an ultimate vacuum of 55 mbar and a maximum flow rate of 2.6 l/min.

Simplified design along with intelligent features of the KNF pumps help this inkjet printer manufacturer maintain ink integrity and printhead reliability for their DOD inkjet printers. This presents the customer with a product that offers long service life and precision operation across multiple industrial applications.

For information: 

KNF

NVC 830 HP

NVC 830.3