K Factor Nozzle

[Berk Boyraz]

Asfamiliar as the subject of water flow may be to some, there are still those that do not have the opportunity to apply it daily. As a result, they may not be as familiar with water flow as those of us who do.

One comment that I often hear is that fixed and selectable gallonage nozzles are limited to the rating or setting. This is far from true. Any fixed or selectable gallonage nozzle can be under or over-pumped depending on what the desired outcome is.

Now, obviously you would not want to go to extremes and generate too much nozzle reaction or have too low of a pressure, but there is some wiggle room for deviation from actual flow and pressure ratings.

The flow rating on a fixed or selectable gallonage nozzle is simply how much flow it will deliver at that base nozzle pressure. This flow rating is a minimum, but not to exceed 10% above the flow rating at the rated base nozzle pressure..

The flow and pressure rating are indicated by what is known as a K-factor or K-value. This value can determine flow at any given pressure or vice versa, pressure at any given flow. This information is illustrated on the flow curve found in the technical support materials for your nozzle.

What this shows is that a 150 at 50 nozzle and a 185 at 75 nozzle are essentially the same give or take a few GPM and PSI. If you work the formula for them, you will also find that a 160 at 50 and 200 at 75 nozzle are essentially the same.

Understanding the K-value can help you develop discharge pressures for various flows based on the conditions you face. If two 150 GPM handlines is your standard, you can easily deliver at an almost 25% higher application rate if needed by understanding what your nozzles are capable of and figuring out the required pump discharge pressure for the additional flow and nozzle pressure.

Keep in mind that over pumping any given nozzle will increase your nozzle reaction. You and your crew should be mindful of this as it increases strain on the firefighter at the nozzle and can increase the risk of injury.

In fire protection engineering, the K-factor formula is used to calculate the discharge rate from a nozzle. Spray Nozzles can be fire sprinklers or water mist nozzles, hose reel nozzles, water monitors and deluge fire system nozzles.

Care should be exercised not to intermix K-factors from Metric and English units as the resulting factors are not equivalent or interchangeable.

Let's take an high pressure water mist nozzle as example, the operating pressures are from 10Mpa to 14 Mpa and the K factor is 1.00.

The ratio is a multiplier applied to the nozzle size to derive a suitable extrusion width. I think they've done it this way to simplify working with different nozzle sizes. The default of 1.2 works well IME.

A good general guideline is to use extrusion widths between 100 and 120% of your nozzle size. I usually leave them set to 0 in PrusaSlicer, which will use values derived from the nozzle size. This lets me use one Print Settings preset with any nozzle size.

You can definitely experiment with these, and if you stick to quality nozzles (E3D, P3-D, TriangleLab), you can go up to roughly 200% of nozzle size and still get good quality, provided you don't mind the more rounded corners it produces. If I'm printing something that consists primarily of perimeters, I'll often crank up the perimeter and external perimeter widths higher. I've even gone with wide 200% single perimeter prints giving "pseudo vase mode" speeds but still very strong walls. If I'm doing a large print with lots of infill and I'm only using infill to support top surfaces, I'll specify a narrower width for infill.

In fire protection engineering, the K-factor formula is used to calculate the volumetric flow rate rate from a nozzle. Spray nozzles can for example be fire sprinklers or water mist nozzles, hose reel nozzles, water monitors and deluge fire system nozzles.

K-Factors have also previously been calculated and published using the United States customary units of pound per square inch (psi) and gallon per minute (gpm). Within the United States, US measurements are still often used instead of metric.[3][4]

Care should be exercised not to intermix K-factors from metric and Imperial/US units, as the resulting factors are not equivalent or interchangeable.[5] In case of mix-ups, results can be catastrophic[broken anchor].

The table below provides measured nozzle geometry information obtained via various techniques as discussed in Kastengren, 2012. Silicone mold analysis has also been performed for nozzle 675. Orifice exit boundaries (X-Y profiles measured via optical microscopy) are provided in the table as text files (*.txt), centered on the axis of the injector to highlight the offset of the orifice at the outlet. Equivalent diameter along the axis of the orifice is given based on tomography or phase-contrast analysis. To remove artifacts of inlet rounding, we fit the equivalent diameter from 10-80% of the hole length and then extrapolate this fit to the inlet and exit of the nozzle to determine the K factor.

*Note 210675 tomography has been updated based on high-resolution x-ray tomography performed at CNRS, France by Ali Chirazi. The raw data was smoothed to create the stl file given, which was recommended for computational grid generation for ECN3.

Below is a schematic of the definition used for the hole orientation. The orifice exit is located on the origin of the cartesian coordinates system used (X, Y, Z). The orientation angle θ together with the exit offset represent the location of the orifice with respect to the axis of the injector body and the fuel tube. Note that the orientation angle is also expressed as φ, the angle used by the manufacturer. However, φ is referenced with two pins to hold the nozzle in position with respect to the injector body, which are not visible from outside (without unmounting the nozzle). For that reason, θ is defined as the angle between the fuel tube and the actual orifice in the counter clockwise direction when facing the injector tip. The offset presented in the table above corresponds to the distance between the axis of the injector and the axis of the orifice at the exit.

Stereo lithography files (.stl) derived from x-ray tomography are provided for each nozzle in the table according to the injector orientation convention, except the axial distance in these files is the z coordinate. For modeling these nozzles, be aware that the actual nozzle surface is not portrayed perfectly in these stl files because of measurement artifacts, as discussed by Kastengren, 2012. Efforts are currently underway to produce more refined surface files. An idealized hexahedral mesh has also been generated for nozzle 675.

While some individuals may be well-acquainted with the subject of water flow, there are others who lack the opportunity to apply this knowledge in their daily lives. Consequently, their familiarity with water flow may not be as extensive as those of us who have regular exposure to it.

The flow rating on a fixed or selectable litreage nozzle simply indicates the amount of flow it delivers at the base nozzle pressure. However, this flow rating is not a strict limit; it allows for a maximum increase of 10% above the rated flow at the base nozzle pressure, in compliance with the NFPA (National Fire Protection Association) 1964 standard.

The flow and pressure ratings are indicated by a K-factor or K-value. This value determines the flow at any given pressure or vice versa, the pressure at any given flow. You can find this information illustrated on the flow curve, which can be found in the technical support materials for your specific nozzle.

This calculation demonstrates that a 568 LPM nozzle at 345 kPa and a 654 LPM nozzle at 517 kPa are essentially equivalent, with only a small difference in LPM and kPa. Similarly, a 605 LPM nozzle at 345 kPa and a 755 LPM nozzle at 517 kPa yield comparable results.

There were way more paths before but I increased the "Maximum allowed detour factor" in the advanced tab, and this did reduce the number of paths (thanks Neatko!). Anything above 6 or 7 doesn't decrease the number of paths anymore.

I've also tried all three "Start point" options including random start points, optimized start points, and custom start points. For custom, I tried 300, 0 0, 300 -999, 0 just to try different ways, but there are still many random paths of the nozzle.

Dunno. Maybe Cura finally thinks better. In my experience Cura always did worse paths than s3d, but maybe they improve it. Afaik for the things I do it always does worse path than s3d, but ofc it might just depend on what you do.

To cut down stringing I just improved my hotend, changed the feeder to allow almost infinite retractions. When you can do as much retractions as you want you only worry about scratching the print (something Cura likes to do). So maybe for your stuff you should stick to cura? For top layer quality I still see s3d as the better option, specially since it allows the user more control, it doesn't hide options thinking for the user and let you do much more tricks. Cura even old versions has been for me a really good click/print but a poor production slicer (production as when you need to do 1000 of the same). Ofc anything works, and cura can work (slow) for most of the cases, but when you control s3d, it can do anything you ask him without hidden stuff or thinking for the user when not asked to do so.

What stops s3d to do longer path traveling? Dunno. Maybe it knows that over crossing path over and over can make the paths overheat and deform, but you ain't doing overhangs so you can use long path travel. Also s3d uses retractions to keep the control of extrusion, but cura loves to hide the mistakes on the infill or in long travels (hiding the dripping).

Thank you! It helps a lot for me a noob to here from the more experienced like you! I will just do whatever works best and was just a bit shocked when, after using S3D for so long, and then to try out Cura, to realize that Cura makes better/cleaner travel paths. I am sure it can be fixed in S3D somehow but I'm just going to use Cura for now!

3a8082e126