Barometric Pressure Regulation for Ink to Printers

Fabricate refillable, resealable fluid containers for each color. Install a barometric sensor in the head space of each bottle. Install a circulation type pressure regualted loop type ink feed with one port feeding the ink jet tube. Use a solenoid valve to regulate the pressure of the ink flow. Establish the ideal ink flow pressure and use feedback from the baro sensor to regulate the pressure on the feed tube to that value. As baro pressure varies you can modulate the pulse width to the feed pressure regulator in real time to get consistent flow. A control unit could be built to monitor all the pumps, valves and ink levels for all the machines from a single control point.

I thought the same thing at first; I think I have a much simpler solution: Find or make plastic BAGS (IV bags?) to store the ink. The bags will automatically adjust for atmospheric pressure, using only the pressure due to the height of the bags above the printhead.

I considered that idea too, at first but after realizing the OP's concern with high precision in measuring the dispensed fluid, i.e. moving the containers up and down small fractions of an inch to establish the proper pressure, I reverted to the more technical approach.

The two ideas combined look good. Bags with height adjusted by linear actuators which are controlled by a barometric pressure transducer.

Why not simply seal the containers holding the ink, and attached air lines with regulators to maintain a constant pressure?

pressurizig with air liners / compressed air can create bubble and print quality may suffer. Better idea is to use a piston - cylinder (hydraulic, as it gives a better pressure and motion control) to maintain constant pressure in the bottle

With a much less exact requirement - engineering printing - we had difficulties with the large bottles as well. So we got 2 or three of each colour regular ink cartidges and refilled them from the bulk bottles. It still requires regular replacement, but, since the IT people knew how and the engineers simply kept getting angry, we just put new ones in every morning. Downtime was scheduled and controlled.

I would suggest to replace the 1/4" tube with a 1/2" or 3/8" tube. that would change the sensitivity of the system in that the pressure differences wouldn't be so critical. For the pressure regulation the plastic bag idea sounds effective enough

Could be : 1. Combined variation of ink level and internal pressure on the surface of the ink : Is the bottle of ink puncture at high point to equilibrate pressure with atmosphere ? If not, it may request a connection to the machine with a plug and dual piping one from low point to the machine for ink and the other one to equilibrate pressure on ink surface with outside pressure. I do not believe that atmospheric pressure is so critical. Variations are minute. Is the ink viscous ? In that case it would be more difficult to equilibrate pressure at the top of the bottle and outside (possibly via a neutral gas to avoid contamination and drying). Could be also in equilibrium with a light plastic bag containing nitrogen at ambient pressure (plastic bag not fully inflated) to avoid contamination. 2. design of tubing : is there low point ( stagnating deposits) or high points (sky of gas) ? This could leead to plug flow : i.e. irregular flow like geyser. 3. Plugging by particles or dry ink ? What is the stability of your ink regarding drying ? contaminant ? dust ? 4. Diameter of the pipe : if the supply is of one liter, I would think that 1/4" is sufficient. Unless the ink is very viscous. Then increasing the diameter looks like a good idea. An as short as possible straight-vertical pipe is also a good idea. 5. What do the guy who is changing the bottles think about it ?

You didn't mention it, but have you done anything to vacuum break the upturned bottles?

There is also the possibility of using a siphon effect, having the bottles open side up, for consistent pressure. The ink jets should not be so sensitive as to be affected by barometric pressure.

one factor in the feed is the smaller hose flinging around ,,im thinking that the print head moves rather swiftly, as most do, if the hose is connected, it also will be giong side to side,, this could be causing some or all of the problems?? the pressurizing the containers seems like the better idea, but might not want to have the containers above the print heads, since it will be forced, the slight pressure shouldnt cause problems with ink, its not thick enough to need a very high pressure, the barametric pressure,dont seem like it would be a factor, its the same on both ends of system, could be more of a thickness of ink, thicker today that yesterday? can you put thinners in ink? this would be a way to test viscosity each day, but would be messy, unless you empty each day to clean up, and startwith a fresh batch each day, then could be set at a specific viscosity, that might help make system more consistant, how long has the system been running? is this problem a new one? theres my 2 cents worth, good luck

for your viscosity control I strongly suggest looking into a industrial viscometers by Norcross Corp (www.viscosity.com) they have in-line and in-tank units that could be tied into the process flow.

Thanks

Similar to wrench's suggestion, but simpler: Fabricate a single, sealable container to house all of the (vented) individual fluid color containers (like a secondary containment). Fit this container with tygon tubing or other suitable tubing for each color. Install a barometric pressure sensor in the head space of the secondary container. Establish the ideal ink flow pressure, and use feedback from the barometric pressure sensor to operate an air pump in conjunction with a solenoid pressure relief valve to pressurize the secondary container appropriately in order to control the ink flow simultaneously from all of the ink containers which would all be held at the same pressure.

Replace the gravity feed entirely with regulated positive pressure. Use nitrogen bottles (cheap, non-hazardous, non-polluting, more reliable than air compressors, and will not oxidize your inks) to provide gas pressure. Since you are using the gas to provide pressure and not flow, operating costs should be negligible.

I seems to me that the height of the surface of the ink in the bottle would be the predominating factor in the ink pressure at the print head. This assumes that the ink bottle is vented and the viscosity of the ink is not a factor in the 1/4" tygon tube. For instance, if the ink bottle is say, 12" high and the the specific gravity of the ink is the same as water, the pressure of the ink at the print head is 1/2 psi higher with a full bottle vs. the pressure at the print head with an almost empty bottle. (Difference of 12" water column.) The trick would be to maintain the surface of the ink level at a constant height. This could be done by having the bulk ink bottle feeding an intermediate open-topped vessel. A constant level could be maintained by inverting the ink bottle over the open vessel with a drip feed or with a sealed ink bottle with a tube set to the required height that would allow the ink to drain until the lower ink level covered the end of the tube blocking further draining of the ink bottle until the surface level dropped below the end of the tube. If you can imagine those "automatic" dog water bowls where an inverted water bottle replenishes the bowl to a given level.

Assuming there is some type of vacuum relief to the bottle and that the issue is the height of the column of ink, consider suspending the bottles from springs that would lift the bottle up as the ink is used to maintain a fixed column of ink. By selecting the right mass for the holder and the right spring, it should be possible to get a linear response in a 1 to 1 ratio to the ink level in the bottle.

Call the ink cartridge manufacturer to obtain the exact characteristics of how the ink cartridges operate. Then simulate with your own ink containers. The manufacturer may even have a larger cartridge available to purchase. Of course, I am assuming that you are using your own bottles at present.

In the system you describe, (inverted bottles), you don't mention venting. If you install two lines per bottle, one opening at the bottom to deliver ink, and one extending above the ink level to equalize pressure, your fluid pressure should then be regulated only by 'head` and will not vary so widely. I suspect you had partial vaccums in the bottles, being randomly releived by bubble venting, which would give rise to the kind of problem you describe.