Stream Speed Standard

[DX]

[Output in mL per second/1 million] cubed divided by [nozzle area in mm/1 million] squared = stream speed in m/s

There we go. I would rather have x rating back in though. I meant x as in times rating, not as a variable. x rating is the same as saying output in mL per second! [20x is 600mL/second]

[Ben]

Never took a look at this, but my formula is a lot simpler. I'm not even sure if what was posted is correct.

O - output in mL/s
D - diameter of nozzle is mm

speed in m/s = 4*O / pi*D^2

Really easy to remember and every result it has given me appears correct.

I think this forumula will be installed in our review system in the future to automatically give approximate initial speed for water guns based upon the statistics available.

[joannaardway]

Sounds good - I'm just so used to using any old unit that I forget that people occasionally have trouble converting them.

For the reviews - you will need to know the nozzle diameter - not the most common stat for reviews.

So - specify somewhere that people should mention that if they submit a review.

[Ben]

Nozzle diameter is not too hard to take. I'll be taking detailed statistics and writing new reviews for all water guns I have access to, so we'll have more to work with. I have a digital caliper too, so nozzle diameter is easy to take unless the diameter is very small. If the diameter is too small, I'll probably compare against drill bits. If a 1/16" (~1.5mm) drill bit is too big, I'll just round up to that.

I also think I should say that you can't use this formula to calculate output of a different nozzle size. Some people might get that impression. The flow valve varies with the nozzle diameter. Some people might think you can use it for that, but it would be a very rough approximate at best. You'd be better off guessing based upon experience in my opinion.

[joannaardway]

The interesting truth is that flow is roughly proportional to nozzle diameter.

So, for a given soaker, the stream speed should be similar for all nozzles.

[DX]

I doubt that given simple observations. Such as a 12x 21K nozzle vs the riot blast. Medium-sized, fast stream vs big-sized, extremely slow stream. I can tell very easily that the stream speed is different, for the difference in ranges is at least 40ft [60 vs ~15].

I like Ben's formula quite a bit, since it doesn't make you convert units, as long as you always use mm and mL for measuring output and nozzle diameter. SM will adopt this formula for initial stream speed in reviews. I will give the metric m/s and the standard ft/s though, since I can't visualize short metric distances [under 50m] very well.

I also still want to try 0-x, as an additional add-on. Instead of 0-30ft, 0-whatever the max range is. That is much more useful than the 30ft figure. Knowing how fast your stream hits its max range is a pretty nice thing when you are in the middle of a firefight. That is also nice to know when dodging, since if you know the enemy's stream speed to max range, you can time your dodge near perfectly.

[joannaardway]

A riot blast spreads out and will slow down very fast.

Range and stream speed are linked, but that doesn't mean that one should be used to prove the other.

It's good to hear that this calculation is going to be used semi-universally.

Of course, if I buy a chrono for measuring launched projectiles, then I'll do some measurements at after say 5m for my soakers.

I still know the nozzle diameters of the nozzles on my original 2700 , and I can look up output on isoaker, so I can work out what the 32-balloon K-mod did for it.

Final point about the 0-x measurement - I would vote 0-"something about half range" So maybe 15 or 20ft.

[isoaker_com]

Speed----------------

* For a soaker with measured output of 300mL/sec;

nozzle diameter:
3.5mm => 31.2 m/s
3mm => speed 42.4 m/s
2.5mm => speed 61 m/s
2mm => 95.5 m/s

* For a soaker with nozzle of 2mm;

measured output:
150mL/sec (5x) => 47.7 m/s
180mL/sec (6x) => 57.3 m/s
210mL/sec (7x) => 66.8 m/s

* For a soaker with a measured output of 35mL/sec;

nozzle diameter :
0.5mm => speed 178.3 m/s
0.75mm => speed 79.22 m/s
1mm => speed 44.6 m/s

-----------------------------------

The point of these sample calculations is just to highlight the importance of accurate nozzle diameter and output measurements. I'm particularly concerned about measurement of small nozzle diameters as a minor differences in nozzle diameter measurements yields huge differences in reported stream speeds. This is apparent in the calculations since diameter/radius has the exponent tied to it whereas output does not.

I do like the idea of reporting stream speeds, but am a little wary due to problems associated with accurate measurements of nozzle diameters (I have more faith in measuring output in general than measuring nozzle areas).

[Ben]

Those situations don't seem typical (but admittedly, they don't have to be as examples). To see what is typical, I measured the CPS 1200 I have. 4.42 mm nozzle with 141 mL/s reported output (from iSoaker.com). That's 9.2 m/s initial velocity. Sounds reasonable to me. I think you'd be really lucky to get 10X from a 3.5 mm nozzle!

Either way, if I do implement any sort of approximate speed, it'd be noted that these are calculations based upon the output and nozzle diameter. They are not completely accurate even with the most accurate output and nozzle diameters, and only apply for the first fraction of a fraction of a second before the extreme deceleration hits the stream.

[isoaker_com]

Soaker output 141mL/sec:
nozzle diamter:
4.4 mm => 9 m/s
4.3 mm => 10 m/s
4 mm => 11 m/s
5 mm => 7 m/s

Soaker output 30mL/sec:
1mm => 38 m/s
1.3mm => 23 m/s
1.5mm => 17 m/s
1.8mm => 12 m/s
2mm => 9.5 m/s


----------------------------
I'll admit my original diameter number example for the 10x is probably too small for those streams , but my concern remains, particularly for small nozzles. What is the diameter of a typical 1x stream? 1mm? 1.5mm? 2mm? The 1/2mm step yields quite dramatic reported stream speed differences. Even at ~1/3mm steps, you're looking at 5m/s (~16ft/s) differences in reported values.

Stream speed will be more accurate for larger, longer firing nozzles as both nozzle diameter and output can be measured more accurately as both stats are easier to measure. However, for soakers with small nozzles or short shot times, nozzle or output measurements will be much less accurate, resulting in a huge range in calculated speeds.

Putting on a disclaimer is a good start, but I fear misinterpretation as many don't read/understand disclaimers. I'd like to also include speed standards on iSoaker.com, but just want to be more confident about measurements and their effects on the resulting stats.

[joannaardway]

Drill bits tend to come in 1/64ths - which works out as a .4mm jump between them.

Guesses can be made - if one drill fits, but slightly loosely and the next size up won't then a .2mm jump can be estimated. So accuracy is likely to be to be fairly high.

Larger nozzles are easily measured with vernier calipers or similar, and even a small nozzle could be measured with a little effort. However measuring with calipers down the nozzle shrouds on many soakers may be a challenge.

I think the use of this for homemades could be sensible - people know what size nozzle they have drilled, and measuring output isn't that hard.

Measuring stream deceleration is going to be much harder though.

Perhaps some form of Excel spreadsheet, a known range, and the intial velocity could be used to estimate this - another thing to do for the site - it won't be too much work, I've already written a balistics spreadsheet.

[isoaker_com]

Additional thought: stream speeds can be roughly calculated from ranges of level streams (actually, this is how it is described here: SSCentral Stats). If held at a height of 1m from the ground, a level shot will hit the ground in ~0.452 seconds thanks to gravity (assuming it stays constant throughout the duration of the stream). Thus, take the range of a level shot and divide it by 0.452 seconds (can be done for all the stats at iSoaker.com since I used a height of ~1m when doing level shots) to find out the stream speeds.

Use that, here are some numbers:
Flash Flood nozzle ~46.4 feet/sec
Flash Flood stream ~53.1 feet/sec
CPS2000 ~65.3 feet/sec
CPS1000 ~50.8 feet/sec
XP150 ~43.6 feet/sec

Unlike Joanna's formula, this one gives an average speed of a stream, not initial exit velocity. However, it works without needing to do nozzle measurements, thus can be applied to pretty much any nozzle shape easily. To get averages for spreading blasts, one needs to approximate where the 'middle' of the end splash occurs when measuring the range.

Forgot I never posted this thought here before...

[Drenchenator]

Unlike Joanna's formula, this one gives an average speed of a stream, not initial exit velocity.

Actually, since the average output was inputed into the flow formulas, the average velocity was given. To find the true exit velocity (when the gun is first fired) you would have to involve the idea of instantaneous output, which involves calculus. But this should work fine for what we are doing though considering that the CPS line probably has very consistant output.

[isoaker_com]

Originally Posted by Drenchenator

Actually, since the average output was inputed into the flow formulas, the average velocity was given. To find the true exit velocity (when the gun is first fired) you would have to involve the idea of instantaneous output, which involves calculus. But this should work fine for what we are doing though considering that the CPS line probably has very consistant output.

Uh, Joanna's formula states output, not average output. Also, not sure how others measure their output, but the output numbers on iSoaker.com are based on the first ~1s timepoint. I'd measure using a smaller time increment if I could accurately, but I can't. For sake of argument, I do not believe the output for most soakers drops significantly during the first 1s of firing, even for air-pressure models (well, maybe not true for the CPS2000 that may have a shot time just under 1s). The instantaneous output curve is only an approximation as well as it is based on math, not actual measurement. If you want a 'true' speed, you need something that can measure exit speed without slowing the stream. A pair of light sensors with a fixed distance and a good timing mechanism would work.

[joannaardway]

That is a good way of measuring average stream speed - at least on a level shot.

My calc gives nozzle velocity, so from the data gained from this test, assuming a reasonably accurate impact measurement, deceleration can be estimated.

If we know the start speed, the time and the distance, it's easy enough, as long as we assume a linear model.

From all this information, we can analyse the effects of stream lamination on range, possibly through altering some of my spreadsheets.