Patent Description:
Various examples will be described below by referring to the following figures.

Reference is made in the following detailed description to accompanying drawings, which form a part hereof, wherein like numerals may designate like parts throughout that are corresponding and/or analogous. It will be appreciated that the figures have not necessarily been drawn to scale, such as for simplicity and/or clarity of illustration.

throughout this specification to one implementation, an implementation, one case, an example, and/or the like means that a particular feature, structure, characteristic, and/or the like described in relation to a particular implementation, case, and/or example is included in an implementation, case, and/or example of claimed subject matter. Thus, appearances of such phrases, for example, in various places throughout this specification are not necessarily intended to refer to the same implementation, case, and/or example or to any one particular implementation, case, and/or example, Furthermore, it is to be understood that particular features, structures, characteristics, and/or the like described are capable of being combined in various ways in different implementations, cases, and/or examples and, therefore, are within the scope of the appended claims. In general, of course, as has always been the case for the specification of a patent application, these and other issues have a potential to vary in a particular context of usage. In other words, throughout the disclosure, particular context of description and/or usage provides helpful guidance regarding reasonable inferences to be drawn; however, likewise, "in this context" in general without further qualification refers to the context of the present disclosure.

There may be a desire to cause printing fluid to circulate within and/or in proximity to a fluid ejection device. As used herein, the term fluid ejection device refers to a thermal ink ejection device (TIJ) or piezo ejection device (PIJ), by way of non-limiting example. For example, some printing fluids may include solids, such as pigments, that may settle while the printing fluid remains static or in a state of non-motion. In such cases, fluid flow may be sufficient to keep the solids suspended within the fluids, In other cases, fluids may contain dissolved and/or suspended polymers (e.g., in addition to solids) that may also tend to settle. For example, as liquid evaporates concentration of the dissolved and/or suspended polymers may increase leading to increased viscosity and/or worsening decap. Additionally, components of a fluid ejection device (e.g., fluidic dies of a thermal inkjet device) may experience uneven heating, such as due to operation of resistive and/or thermal elements that may cause hot spots in the device. In such cases, fluidic circulation may also be of interest to dissipate thermal buildup at portions of the fluid ejection device. However, causing fluid to circulate may present certain structural and operational challenges to fluid devices. As used herein, the term "fluid circulation" and like terms refer to fluids that flow within fluid channels, such as within recirculation paths, in order to favorize solid suspension and/or thermal dissipation. To be clear, merely transporting fluids to an ejection chamber of a fluid ejection device is not what is contemplated by the term. Instead, fluid circulation refers to fluid paths that allow printing fluids to flow upon command, such as through fluid return paths (e.g., returning back towards a fluid reservoir). At times, the term recirculation is used to refer to circulation back out of a fluid ejection device, such as back towards a fluid reservoir.

Fluid ejection devices may include ejection nozzles (through which fluids, such as printing fluids, are to be ejected towards a medium or substrate), which openings may present challenges to maintaining a fluidic pressure (and thus a rate of fluid flow, or flux) within a fluid channel. For instance, backpressure within the fluid channels, such as due to ejection of printing fluid, may lead to drops in flux in some situations. By way of example, immediately after ejecting printing fluid from a nozzle, printing fluid may cease flowing through a fluid line, may briefly flow in a wrong direction along at least a portion of a fluid line, and/or may flow much more slowly.

Pressure regulators may be used maintain fluid pressure in a fluid line in a range about a set point, which can be desirable, such as to reduce the effects of backpressure. For example, fluids may flow through a pressure regulator prior to flowing towards fluid ejection orifices (e.g., nozzles), and the pressure regulator may dampen effects of backpressure.

It may be possible to enable fluid circulation within a fluid channel that uses pressure regulators on a fluid line corresponding to the fluid channel. This may be done by opening a fluidic element (e.g., a fluid gate) of the pressure regulator to allow fluid flow (e.g., circulation). However, opening the fluidic element of the pressure regulator to allow fluid circulation may lead to a loss of flux on the fluid channel. The loss of flux may contribute to undesirable print quality, such as due to a loss of control of printing fluid droplet size. As such, fluid circulation may be desirable only at points in time for which a drop of flux may be acceptable, such as while a fluid ejection device is being serviced.

With the foregoing in mind, there may be a desire, therefore, for an approach that will enable the use of pressure regulators (e.g., to dampen backflow spikes) and also allow circulation of printing fluid while a printing fluid ejection device is active (e.g., while ejecting printing fluid) without drops in flux (e.g., without flux decreasing below an operational threshold).

The present disclosure thus proposes a system in which a printing fluid pen has a number of fluid ports. A first fluid port is to deliver a printing fluid to an ejection device of the pen (e.g., an input port). A second fluid port is to direct printing fluid out of the pen (e.g., an output port). A pressure regulator is in fluid communication with the first fluid port. And a valve is in fluid communication with the second fluid port. The valve is to open in response to a negative pressure (e.g., negative pressure exceeding a threshold), to enable fluids within the pen to exit via the second fluid port.

The combination of a valve that opens in response to a negative pressure on the outlet port and the pressure regulator in fluid communication with the inlet port may enable fluid circulation, even while ejecting fluid, without undesirable drops in fluid flux (e.g., without flux decreasing below an operational threshold).

Turning to <FIG>, a block diagram illustrates one implementation of a printing fluid pen <NUM>. As used herein, the term "inkjet" will be used to refer to devices capable of ejecting printing fluids including, but not limited to, inks. Thus, for example, a pen of a three-dimensional (3D) printer may be used to eject an agent that may cause a build material to fuse together as part of an additive printing process. The agent may or may not include colorants, such as pigments. Therefore, by referring to a pen as an inkjet pen is not done in a limiting sense. Indeed, it is intended that such fluid ejection pens could be used in a number of different contexts. Additionally, the term "pen" refers to a structure that may include a housing in which a fluid ejection device and a fluidic die may be arranged along with other components in order to enable ejection of printing fluids. The inkjet pen may be removable in some cases, such as to enable replacement of individual pens without replacing an entire printbar.

In one example, an inkjet pen <NUM> includes a plurality of fluid ports, such as a first fluid port 102a and a second fluid port 102b. The first fluid port 102a is in fluid communication with a regulator <NUM>. As noted above, regulator <NUM> may refer to a component capable of managing pressure on a fluid line (e.g., the fluid lines illustrated by printing fluid lines 104a-104d). In one implementation, for instance, regulator <NUM> may operate by opening a fluidic gate in response to backpressure levels exceeding a threshold (e.g., a negative gauge pressure drops below a threshold valve). By opening the fluidic gate, regulator <NUM> allows more fluid into the fluid line and decreases the backpressure (e.g., increases the negative gauge pressure with an influx of printing fluid).

Regulator <NUM> may be in fluid communication with fluid ejection device <NUM>, which may include a number of fluidic dies, and as shall be discussed in further detail hereinafter, the fluidic dies may be supported by a support component. Fluid ejection device <NUM> may be capable of ejecting printing fluid via nozzles, as illustrated by arrows C. Fluid ejection device <NUM> may be in fluid communication with a valve <NUM>. Valve <NUM> may comprise a check valve, which may protect fluid ejection device <NUM> from printing fluid flowing back via fluid lines 104c and 104d. Instead, valve <NUM> may be opened in response to negative pressure applied at second fluid port 102b (e.g., via a vacuum pump). By way of further example, a check valve may prevent flow of fluid backwards (e.g., flowing back upstream towards fluid ejection device <NUM>).

As shown, then, an example fluid ejection pen (e.g., inkjet pen <NUM>) comprises a plurality of fluid ports (e.g., first fluid port 102a and second fluid port 102b). A first fluid port delivers printing fluid to a fluid ejection device (e.g., fluid ejection device <NUM>) and a second fluid port directs printing fluid out of the pen. A pressure regulator (e.g., regulator <NUM>) is in fluid communication with the first fluid port of the plurality of fluid ports. And a valve (e.g., valve <NUM>) is in fluid communication with a second port of the plurality of fluid ports. In response to negative pressure, the valve opens to enable fluids within the fluid ejection device to circulate and exit via the second port.

<FIG> includes arrows A, B, and C, which illustrate a direction in which printing fluid may flow according to one implementation. For example, printing fluid may flow into pen <NUM> via first fluid port 102a, as demonstrated by arrow A. A portion of the printing fluid may be ejected via fluid ejection device <NUM>, as illustrated by arrows C. Another portion of the printing fluid may be directed out of pen <NUM> via valve <NUM> and second port 102b, as illustrated by arrow B.

It should be apparent from the foregoing description, that it may be possible to modulate a circulation flux. For example, modulation of a positive pressure on first fluid port 102a may lead to increases and/or decreases in printing fluid flux entering pen <NUM> (e.g., directly and/or indirectly). And modulation of a negative pressure on second fluid port 102b may lead to increases and/or decrease in printing fluid flux leaving pen <NUM>. Desired circulation flux may therefore be achieved by appropriately setting pressure values at input and output fluid ports (e.g., fluid ports 102a and 102b).

Turning to <FIG>, example fluid ejection devices <NUM> are illustrated. These drawings show different components of fluid ejection device <NUM> in different examples. Fluid ejection devices <NUM> may be similar in structure and/or operation to fluid ejection device <NUM> in <FIG>. It is noted that the present description uses like element numbers to indicate elements and components that may be similar in structure and/or function. For example, an inkjet pen <NUM> in <FIG> may be similar in structure and/or operation to an inkjet pen <NUM>, as shall be discussed hereinafter in relation to <FIG>. It is noted that portions of the description may refer to structure and/or operation of an implementation, While, in some cases, this discussion may apply to other figures and/or implementations, the reader will understand that this may not always be the case, as the context of the description may make clear.

Returning to <FIG>, fluid ejection device <NUM> includes a support component <NUM> and a fluidic die <NUM>. Support component <NUM> comprises a structure, such as a molded structure like a thermoplastic or an epoxy, that provides physical support to fluidic die <NUM>. Support component <NUM> may be manufactured using a molding process, a machining process, or a layer build-up process, by way of example. Fluid slots 220a and 220b may carry printing fluids towards and/or away from fluidic die <NUM>. Fluidic die <NUM> may comprise a semiconductor material and may include a number of layers making up fluid channels and slots (e.g., fluid feed holes 218a and 218b), ejection chambers, and nozzles (e.g., nozzles <NUM> in <FIG>). Fluidic die <NUM> may also include ejection components, such as resistive components or piezoelectric membranes, by way of example, that may be activated to eject printing fluid from the nozzles.

There may be a space or gap between support component <NUM> and fluidic die <NUM> through which printing fluid may circulate. As illustrated, fluid channel <NUM> may be defined by a gap in support component <NUM> and/or a gap in adhesive layer <NUM>. Fluid channel <NUM> may be used to enable circulation of printing fluid, such as illustrated by arrows A, B, and C, in <FIG>.

In operation, an inkjet pen (e.g., inkjet pen <NUM> of <FIG>) may include a support component (e.g., support component <NUM>) connected to a fluidic die (e.g., fluidic die <NUM>). A fluid channel (e.g., fluid channel <NUM>) may be arranged in relation to the support component in proximity to a backside of the fluidic die. The backside of the fluidic die refers to the surface of fluidic die between the fluidic die and the support component. As such, in some examples, printing fluid flowing through the fluid channel may flow in contact with the backside of the fluidic die.

As described above, the fluidic die may comprise a plurality of fluid feed holes (e.g., fluid feed holes 218a and 218b) and the fluid channel is arranged to be in fluid communication with the plurality of fluid feed holes.

Additionally, in some examples, in addition to providing circulation in proximity to the backside of the fluidic die, the fluid ejection device may also provide fluid circulation within microfluidic channels within the die, as shall be illustrated by <FIG>.

Turning to <FIG>, a fluid ejection device <NUM> is illustrated with components that are similar to those discussed in relation to <FIG>. For example, fluidic die <NUM> may be similar in structure and/or operation to fluidic die <NUM> of <FIG>, adhesive layer <NUM> may be similar in structure and/or operation to adhesive layer <NUM> of <FIG>, and support component <NUM> may be similar in structure and/or operation to support component <NUM> of <FIG> also illustrates fluid slots 220a and 220b, fluid channel <NUM>, and fluid feed holes 218a and 218b, which are similar in structure and/or operation to those discussed in relation to <FIG>. The combination of fluid channel <NUM>, fluid slots 220a and 220b, and fluid feed holes 218a and 218b may be referred to collectively as a fluid flow path <NUM>, as illustrated by arrows, A and B. Additionally, fluid may be ejected from nozzles, such as nozzle <NUM>, as illustrated by arrow C. An example ejection component <NUM> is illustrated in proximity to a different nozzle and is intended to contemplate thermal-based ejection elements, piezo-based ejection elements, and the like. It is to be understood that ejection elements, such as ejection component <NUM>, may be arranged in each ejection chamber from which it may be desired to eject printing fluid.

In contrast to the arrangement of fluid feed holes 218a and 218b in <FIG>, fluid feed holes 218a and 218b in <FIG> are also in fluid communication within fluidic die <NUM> (e.g., within microchannels). As such, printing fluid may enter an ejection chamber via a first fluid feed hole (e.g., fluid feed hole 218a), traverse an ejection chamber, and a portion of the printing fluid that is not ejected may subsequently flow out of the firing chamber and the fluidic die via a second fluid feed hole (e.g., fluid feed hole 218b). This fluidic path is illustrated by arrow B. In one implementation, one or more circulation components may be arranged within fluidic die <NUM> in order to cause printing fluid to enter fluid feed hole 218a from fluid channel <NUM>. Additionally (or alternatively), activation of ejection components (e.g., resistive elements) may exert a fluidic pressure within the fluid path illustrated by arrow B to cause fluid (e.g., all or part of the fluid indicated by the arrow A) to enter fluid feed hole 218a. Such circulation may be enabled by activation of a circulation component <NUM>, by way of example. Circulation component <NUM> may comprise a resistive component, such as an embedded resistor, that may generate heat in response to current flow. Activation of circulation component <NUM> may facilitate fluid circulation, such as illustrated by arrow B. It is noted that while but a single circulation component <NUM> is illustrated, a number of circulation components may be arranged within other fluid feed holes to facilitate circulation. It may be in some cases that fluid may circulate through individual microchannels, as opposed to circulating through all ejection chambers concurrently. In other implementations, rather than using circulation components <NUM>, due to external pressure (e.g., due to a pump external to fluid ejection device <NUM>), printing fluid may be forced to enter fluid feed hole 218a.

As noted above, the combination of a plurality of fluid ports (e.g., fluid ports 102a and 102b in <FIG>), a regulator (e.g., regulator <NUM> in <FIG>), and a valve (e.g., valve <NUM> in <FIG>), in combination with fluid ejection device <NUM> may enable circulation of printing fluid without a decrease in fluid flux.

In operation, therefore, printing fluid entering fluid ejection device <NUM> may be caused to be both ejected (in part) and to recirculate (in part). Thus, as shown by arrow A, printing fluid may enter a fluid slot (e.g., fluid slot 220a), may travel through a fluid channel <NUM>, and may exit the fluid ejection device via another fluid slot (e.g., second fluid slot 220b). A portion of the printing fluid may be ejected from a fluidic die (e.g., fluidic die <NUM>) via a nozzle (e.g., a nozzle <NUM>), as illustrated by arrow C. And another portion of the printing fluid may be caused to circulate away from an ejection chamber and out of fluid ejection device <NUM> (e.g., as illustrated by the portion of arrow B traversing fluid feed hole 218b and the portion of arrow A traversing fluid channel <NUM> and fluid slot 220b). The circulation of printing fluid out of fluid ejection device <NUM> may be in response to application of a negative pressure, activation of a circulation element, activation of a plurality of ejection elements, or a combination thereof.

The next drawings focus on the support structure that enables flow of printing fluid in proximity to a back surface of a fluidic die.

<FIG> illustrates an implementation in which fluid channels traverse a width of fluidic dies, while <FIG> illustrates an implementation in which fluid channels traverse a length of fluidic dies. <FIG> may include components similar to those discussed previously. For example, a support component <NUM> may be similar to support components <NUM> illustrated in <FIG>. Likewise fluid slots 320a and 320b may be similar to fluid slots 220a and 220b in <FIG>.

<FIG> also show example die supports <NUM> that may support and/or secure fluidic dies (not shown; see, e.g., fluidic die <NUM> in <FIG>) into support component <NUM> and/or provide protection against potentially damaging contact (e.g., by media, by a service blade, etc.).

Support component <NUM> may include gaps 326a-326d within the structure, such as to allow printing fluid to flow from fluid slot 320a to fluid slot 320b, as illustrated by arrows A. It should be understood that gaps 326a-326d may correspond to fluid channel <NUM> in <FIG>, by way of example. Additionally, adhesive dots may be applied to support surfaces 328a-328c to secure the fluidic die to support component <NUM>. in one example, there may be gaps in the adhesive layer corresponding to gaps 326a-326d. In some cases, a fluid channel (e.g., fluid channel <NUM> in <FIG>) may be formed along a backside of a fluidic die without gaps 326a-326d. For instance, if a sufficiently thick adhesive layer is applied, gaps in the adhesive layer (e.g., similar to gaps 326a-326d in support component <NUM>) between adhesive dots may be sufficient to form a fluid channel.

In contrast to <FIG>, in which gaps 326a-326d form fluid channels that extend across a width of the fluidic die, <FIG> illustrates an example in which fluid channels are arranged to run lengthwise across a back surface of the fluidic die.

<FIG> illustrates components that are similar to those discussed in <FIG>, including support component <NUM>, fluid slots 320a-d, gaps 326a and 326b, and die supports <NUM>. Nevertheless, gaps 326a and 326d are arranged with respect to fluidic dies such that printing fluid will enter gaps 326a and 326b (corresponding to, for instance, fluid channel <NUM> of <FIG>) by fluid slots 320c and 320d. The printing fluid will traverse the length of the backside of the fluidic die, and will exit gaps 326a and 326b via fluid slots 320a and 320b. In some implementations, more than one pair of input and output ports (e.g., fluid slots 320a and 320c) may be formed within a gap (e.g., gap 326a). For instance, along one channel defined by a gap, there may be a first input port followed by a first output port, then a second input port followed by a second output port, etc. Such an implementation may be desirable to reduce a pressure drop along the length of the fluid channel defined by the gap in support component <NUM>.

The next drawing, <FIG>, illustrates an example fluid pen, including those structures discussed above, in relation to <FIG>,.

<FIG> illustrates an inkjet pen <NUM> and illustrates a flow of printing fluid in through a first fluid port and out of a second fluid port (e.g., fluid ports 102a and 102b in <FIG>), where fluid flow out of pen <NUM> is illustrated by broken arrows and fluid flow into pen <NUM> is illustrated by solid arrows. A cap <NUM> refers to a structural component to enclose a top portion of pen <NUM>, and may be in a suitable material including, but not limited to, thermoplastics. A filter <NUM> may be arranged in a fluidic plate <NUM> designed to facilitate directing fluid flow into and out of pen <NUM>. For example, due, among other things, to recirculation of printing fluid, colorants may stick together and increase in size. Additionally, dust and debris may accumulate within circulating printing fluids. In such cases, filter <NUM>, which may comprise a screen or a membrane, by way of non-limiting example, and may remove the undesirable particles (e.g., colorants, debris, etc.) from the printing fluid. Suitable materials for fluidic plate <NUM> may include thermoplastics, ceramics, glass, and metals, by way of non-limiting example. In one example, valve <NUM> and regulator <NUM> may be arranged within a body <NUM>; valve <NUM> may enable flow of printing fluid out of pen <NUM>; and regulator <NUM> may maintain flux for printing fluid entering fluid ejection device <NUM>. A carrier <NUM> may act as a support structure, such as including support compound <NUM> discussed above in <FIG>. Carrier <NUM> may include other components, including a fluid fan-out manifold, by way of non-limiting example. An adhesive layer <NUM> is illustrated as by connect carrier <NUM> to fluid ejection device <NUM>.

It is noted that in one implementation, one pen <NUM> may house a fluid line and supporting components (such as a filter, a pressure regulator, a check valve, etc.) for a single color printing fluid (e.g., black). Additional pens may be used to support fluid lines for additional colors of printing fluid (e.g., cyan, magenta, yellow, white, etc.).

The next two drawings (and associated description) will discuss how the elements of <FIG>, <FIG>, and <FIG> may operate together in order to enable fluid circulation within a pen while the pen is active (e.g., ejecting fluid) without reductions in printing fluid flux.

<FIG> and <FIG> illustrate example printing fluid delivery systems <NUM> configured to enable circulation of printing fluid, such as across a backside of a fluidic die, without a reduction in flux, such as using an inkjet pen <NUM>, similar in structure and/or operation to inkjet pen <NUM> in <FIG>. Fluid ejection devices <NUM> may be similar in function and/or operation to fluid ejection device <NUM> in <FIG> and fluid ejection devices <NUM> in <FIG>. Regulator <NUM> may be similar in structure and/or operation to regulator <NUM> in <FIG>. And valve <NUM> may be similar in structure and/or operation to valve <NUM> in <FIG>.

<FIG> also illustrates a filter <NUM>, a printing fluid supply <NUM>, a pump <NUM> (e.g., for pressurization at a first port), a pump <NUM> (e.g., for creating a vacuum at a second port), a pressure regulator <NUM>, a flow restrictor <NUM>, an input pressure regulator <NUM>, and a thermal regulating component <NUM>. A controller <NUM> may be in communication (e.g., via electrical signals exchanged) with components of printing fluid delivery system <NUM>.

In one implementation, printing fluid supply <NUM> refers to a reservoir capable of receiving, storing, and releasing printing fluid. In examples herein, printing fluid may exit printing fluid supply <NUM> and may traverse fluid supply lines towards pen <NUM>. Printing fluid that is not ejected by pen <NUM> may be recirculated back to printing fluid supply <NUM>, as illustrated.

Pump <NUM> may be capable of applying a positive pressure on a fluid supply line, such as to cause printing fluid to flow towards pen <NUM>. Pump <NUM> may take any suitable form including electromechanical and solid-state pumps, by way of non-limiting example.

in one implementation, a subloop through input pressure regulator <NUM> may be used to help maintain constant input pressure at fluid port 502a. For instance, as flux changes within pen <NUM> (e.g., due to pressure changes on a fluid line due to changes in drop ejection flux), input pressure regulator <NUM> may comprise a gate to dynamically open and/or close based on pressure on a fluid line after pump <NUM>.

Thermal regulating component <NUM> refers to components capable of heating and/or chilling printing fluid prior to transmission thereof to pen <NUM>. For example, there may be a desire, such as when a printing device is first turned on, to heat a fluidic die, such as to enable desirable operational parameters. Heating of printing fluid may also be desirable in order to reduce printing fluid viscosity. Similarly, at times there may be an interest in chilling a print head. For instance, at times a fluidic die may have portions that are exceeding a desired temperature. Additionally, in some cases there may be a desire to increase a viscosity of a printing fluid. Thus, in such cases, there may be a desire to transmit chilled printing fluid to pen <NUM>. As should be appreciated, a thermal regulating component <NUM> may be desirable to yield a desired print quality (PQ).

After pressurization by pump <NUM> and/or traversing thermal regulating component <NUM>, printing fluid may enter pen <NUM> via a first fluid port 502a, similar to as has been discussed above. Printing fluid may flow through filter <NUM> in order to remove any solids or debris exceeding a desired size, as discussed above. As should be apparent, then, in one case, a filter (e.g., filter <NUM>) may be in fluid communication with a pressure regulator (e.g., regulator <NUM>).

A portion of the printing fluid may be ejected via fluid ejection devices <NUM>, as discussed above, and may be allowed to flow out of fluid port 502b as valve <NUM> is opened, such as in response to application of a negative pressure. In one example, negative pressure may be applied to valve <NUM> by pump <NUM>. Pump <NUM> may comprise any suitable form of electromechanical or solid-state component (among other things) capable of applying a negative pressure on fluid port 502b. Flow restrictor <NUM> and regulator <NUM> may work in concert to ensure that a vacuum pressure does not exceed an acceptable threshold at port 502b analogously to the operation of regulator <NUM> and input pressure regulator <NUM>. For example, if excessive pressure were to be applied by pump <NUM>, a flux of printing fluid may exceed a threshold for providing acceptable pressure to fluid ejection devices <NUM>. And flow restrictor <NUM> and regulator <NUM> may reduce such an occurrence.

It should be understood that controller <NUM> may be capable of enabling the operation of components, as discussed above, such as by transmitting signals to a desired component, such as via an electrical contact of a pen. Once received by the pen, the signals may be transmitted to enable operation, such as discussed above (e.g., causing ejection of printing fluid from a fluid ejection device).

<FIG> includes components similar in structure and/or operation to those discussed in <FIG>. For instance, <FIG> illustrates an inkjet pen <NUM>, in fluid communication with a printing fluid supply <NUM>, a pump <NUM>, a thermal regulating component <NUM>, a pressure regulator <NUM>, a vacuum regulator <NUM>, and a vacuum pump <NUM>, <FIG> also illustrates a degas component <NUM>, capable of removing gasses from printing fluid, such as by allowing air bubbles to separate from the fluid and be vented elsewhere. <FIG> also shows an inlet trunk line 503a through which printing fluid flows, after being pumped from pump <NUM>. Printing fluid enters a number of fluid ejection devices <NUM> for ejection via fluidic lines and a first fluid port 502a. Printing fluid that is not ejected by fluid ejection devices <NUM> may be recirculated back towards printing fluid supply <NUM> via second fluid port 502b, may traverse a flow restrictor <NUM>, and be directed to another fluid trunk line, this time an outlet trunk line 503b. As described, above, a valve in fluid ejection devices <NUM> may enable flow of printing fluid out of second fluid port <NUM>, even while printing, without a reduction in flux.

<FIG> illustrates a method <NUM> including blocks <NUM>, <NUM>, and <NUM>. At block <NUM>, a printing fluid is caused to enter a pen (e.g., pen <NUM> of <FIG>) via a first port (e.g., fluid port 502a of <FIG>). As noted above, fluid flow may be engendered responsive to operation of a pump, activation of ejection components, and activation of circulation components, by way of non-limiting example. Returning to example method <NUM>, the printing fluid is to traverse a pressure regulator (e.g., regulator <NUM> of <FIG>) and enter a fluid ejection device (e.g., fluid ejection device <NUM>).

At block <NUM>, a plurality of ejection elements are activated in the fluid ejection device to cause a first portion of the printing fluid to exit the fluid ejection device (see, e.g., arrow C in <FIG>).

At block <NUM>, a negative pressure is applied to a valve (e.g., valve <NUM> in <FIG>) in fluid communication with a second port (e.g., second fluid port 502b in <FIG>) of the pen to cause a second portion of the printing fluid to circulate across the back surface of the fluid ejection device (see, e.g., a second portion of arrow A in <FIG>) and to exit the pen while the plurality of ejection elements are being activated.

Claim 1:
An inkjet pen (<NUM>, <NUM>, <NUM>) comprising:
a plurality of fluid ports, a first fluid port (102a, 502a) configured to deliver printing fluid to a fluid ejection device (<NUM>, <NUM>, <NUM>) from a printing fluid supply (<NUM>) and a second fluid port (102b, 502b) to direct printing fluid out of the pen;
a pressure regulator (<NUM>, <NUM>, <NUM>) in fluid communication with the first fluid port (102a, 502a) of the plurality of fluid ports; and
a valve (<NUM>, <NUM>, <NUM>) in fluid communication with the second fluid port (102b, 502b) of the plurality of fluid ports;
wherein, in response to negative pressure, the valve (<NUM>, <NUM>, <NUM>) is configured to open to enable fluid within the pen that is not ejected by the fluid ejection device (<NUM>, <NUM>, <NUM>) be recirculated towards the printing fluid supply (<NUM>) via the second fluid port (102b, 502b).