Principles and Applications of Siphon Ink Supply System

1. Siphon Ink Supply System

A siphon ink supply system is an ink delivery method that operates based on the principle of atmospheric pressure difference.

2. Siphon

A siphon is a physical phenomenon in which a liquid rises automatically within a tube. It is caused by a pressure difference formed inside the tube. When one end of the tube is immersed in liquid, and the other end is positioned lower, the liquid will flow upward automatically until equilibrium is reached.

3. Siphon Ink Supply

Siphon ink supply is a method of delivering ink using the siphon principle and is commonly used in continuous ink supply systems (CISS) for inkjet printers.
In this system, an external ink bottle is connected to the printer’s ink cartridge via ink tubes. Using the siphon effect, ink continuously flows from the ink bottle into the cartridge, enabling an uninterrupted ink supply.

4. Siphon Principle

The siphon principle is based on the principle of communicating vessels. When the siphon tube is completely filled with liquid and contains no air, the liquid level at the inlet side is higher, while the outlet is initially sealed. At this point, the pressure inside the tube is uniform.
Once the outlet is opened, the higher liquid level and greater pressure at the inlet side push the liquid to flow continuously through the tube and exit from the outlet.

5. Siphon Phenomenon

The siphon phenomenon results from intermolecular attraction between liquid molecules combined with a difference in gravitational potential energy. The pressure difference created by the liquid column causes the liquid to rise and then flow to a lower position.

In inkjet printers, the siphon ink supply operates based on this physical phenomenon. Ink in the cartridge is connected to the nozzle through ink tubes, forming a liquid circulation system.
Specifically, ink in the cartridge first flows into the ink tube under gravity. As the ink descends inside the tube, one end of the tube remains immersed in ink while the other end is positioned at the lower nozzle location. Due to this height difference, the liquid rises automatically, creating a siphon effect. The ink is drawn upward through the tube and then, under printer control, ejected through the nozzles.

6. Siphon Ink Supply vs. Traditional Gravity Ink Supply

Compared with traditional gravity-fed ink systems, the siphon ink supply has the following advantages:

① It ensures continuous ink delivery and prevents printing interruption caused by an empty cartridge.
② It provides better control of ink flow rate, ensuring proper pressure at the nozzle for improved print quality.
③ It reduces ink splashing and uneven ink ejection, thereby enhancing overall print quality.

7. Precautions for Siphon Ink Path Connections

① Proper coordination between the printhead and waveform is required to generate suitable pressure and jetting speed for optimal print results.
② Connections between the ink cartridge and ink tubes must remain airtight to prevent ink leakage or evaporation.
③ Ink viscosity must be appropriate; viscosity that is too high or too low will negatively affect the siphon effect.

8. Siphon Ink Supply Method (Working Conditions)

To generate a siphon effect, the outlet of the bent tube must be lower than the inlet.

Let the liquid level at the inlet be plane A and the liquid level at the outlet be plane B. Atmospheric pressure acting upward on both planes is P₀. However, in the right-side tube below plane A, there is a liquid column of height h. Therefore, the pressure at plane A inside the right tube is:

P = P₀ − ρgh

Since P₀ > P, this pressure difference causes the liquid to flow toward the right tube and eventually exit at point B.

Note:
The formula for liquid pressure is:
p = ρgh

Where:

• p = liquid pressure (Pa)
  

• ρ = liquid density (kg/m³)
  

• g = gravitational acceleration (≈ 9.8 m/s²)
  

• h = liquid depth (m)
  
  

To create a meniscus negative pressure at the nozzle surface, the ink level in the cartridge must be set lower than the nozzle surface due to ink surface tension.

9. Applications of the Siphon Ink Supply Method

① When the ink cartridge is positioned behind the carriage, and its liquid level must be lower than the nozzle surface, the machine can only be used for roll-to-roll printing.
② When the ink cartridges are positioned at one or both ends of the machine and connected to the printhead via drag chains, the printer can be designed for either roll-to-roll printing or flatbed material printing.

PS:
The typical liquid level difference is approximately 70 mm.