Fast Liquid Valve
Original Publication Date: 1976-Nov-01
Included in the Prior Art Database: 2005-Mar-03
Giordano, FP: AUTHOR [+2]
In an ink jet printing system, puddle formation during start-up and shut-down of the system leads to crusting on the nozzle, which, in turn, results in drift of nozzle directionality. Prevention of puddle formation is accomplished by fast turn-on and turn-off of a liquid jet.
Fast Liquid Valve
In an ink jet printing system, puddle formation during start-up and shut-down of the system leads to crusting on the nozzle, which, in turn, results in drift of nozzle directionality. Prevention of puddle formation is accomplished by fast turn- on and turn-off of a liquid jet.
The sharp turn-on of a liquid jet is accomplished by using the excess liquid pressure, sometimes called "water hammer pressure", which is created due to the sudden blockage of fluid flow through a liquid line.
The water hammer pressure Ph is defined as:
Ph = Rho u c
Rho is the liquid density;
u is the liquid velocity before blockage; and
c is the sound speed in the liquid.
Operation of the valve is as follows: Valves V1 and V2 are in the open position, as illustrated, allowing liquid to flow from a source (not shown) in the direction of the arrow to a sump (not shown), thereby bypassing the nozzle N, with the liquid flowing at a bypassed speed of u. Leakage of liquid into air chamber A is prevented by pressurizing the air chamber at pressure Pa, which need only be a few pounds per square inch (psi) above atmospheric pressure. Closing valve V1, as shown in broken lines, causes a shock wave to travel in the reverse direction through the liquid line in the direction of the source, producing a very sharp pressure rise at the nozzle N.
Since C is large, on the order of l500 m/sec for water, the momentary pressure rise is on the same order of magnitude as the liquid suppl...