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Smooth Flow Diaphragm Pumps for Drop-on-Demand Digital Inkjet Help Reduce Complexity

As technology advances, diaphragm pumps are becoming the superior pump option for drop-on-demand printing systems.

Drop-on-demand (DOD) Digital Inkjet Technology continues to evolve and finds new applications. Beyond simply printing graphic images on paper, the latest digital inkjet systems are printing colors and coatings on ceramics, glass, and textiles, and jetting functional fluids for 3D printing, printed electronics, and even biomedical and diagnostic applications. To take full advantage of the advances in printhead technology and ink formulations, a new generation of KNF Smooth Flow Pumps is being integrated into the latest ink delivery systems. The new systems are simpler, more flexible, and more cost-effective.

Many Pumps for Drop-on-Demand Inkjet Needed with Conventional Technology

Conventional recirculating DOD systems are complex and rely on an intricate system of liquid pumps, air compressors and vacuum pumps. In a typical system that uses a mix of different pump types, the ink is stored in a bulk supply tank, where a pump (1) may be needed to mix and agitate the ink to prevent pigment settling. The ink may then be transferred by a pump (2) to a secondary reservoir (3), from where it is transferred by the next pump (4) to a degassing unit which requires a vacuum pump (5).


The degassed ink then flows into a supply header tank (6) from where it passes a filter (7) and then supplies the printhead with a constant recirculating supply of ink. Piezoelectric elements in the print head (8) eject small droplets of ink onto the surface of the object to be printed (9). The unused recirculating ink leaves the printhead and flows back to the return header tank (10). From there, a return pump (11) transfers the ink back to the reservoir tank. Vacuum pumps (12 and 13) provide vacuum above the ink in the header tanks to overcome the hydrostatic head and maintain a small vacuum at the printhead, sufficient to hold the ink meniscus within the nozzle plate. An additional purging pump (14) is used when required for purging and cleaning.

Smooth Flow Technology Reduces Number of Pumps for Drop-on-Demand Inkjet

In the past, the complicated system of two sub-tanks (6 and 10) and their associated meniscus and purge air pumps (12, 13 and 14) was required to maintain a smooth recirculating flow and stable meniscus vacuum at the printhead nozzle plate. Today, thanks to the development of KNF Smooth Flow pump technology, these additional components are no longer necessary.


Instead, the ink can be pumped directly from the recirculation reservoir (A) via a KNF Smooth Flow Pump (B) through the degasser (C) and a filter (D), flowing smoothly through the printhead (E). Unused ink returns to the reservoir (A) via a second Smooth Flow Pump (F). The desired meniscus vacuum is regulated and maintained by controlling the relative speeds of the supply and return pumps (B and F).

New Possibilities for DOD Thanks to Smooth Flow Technology

KNF Smooth Flow Pump technology unlocks new possibilities for recirculating ink delivery systems by offering several technical and economic advantages. The reduction in component count and complexity makes the system smaller, simpler, and less costly to manufacture, operate and maintain. With the ink flowing smoothly through the system, a lower system operating pressure is achieved, reducing the load on the pumps and other system components, extending their lifetimes.


Another advantage of the low pulsation is that the system runs smoothly and quietly and is more energy efficient as well as reliable. Reducing the total volume of ink in the system significantly makes purging, cleaning, and priming quicker and less costly. This reduced system volume can also provide an advantage in multi-pass and direct-to-shape applications where the printhead moves quickly around the object to be printed.

Key Benefits of Diaphragm Pumps for Drop-on-Demand Inkjet

KNF diaphragm pumps have long been the natural choice for inkjet applications. With a wide range of materials, they provide excellent compatibility with even the most challenging ink chemistry and abrasive particles. Diaphragm pumps handle pigmented inks more gently than other positive displacement pump technologies (peristaltic, gear, and piston) and with the introduction of Smooth Flow Technology, the latest KNF diaphragm pumps are now even gentler and ideal for recirculating very sensitive or abrasive particles in functional inks.

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