# Thread: How do you determine the flow from an automatic nozzle on a deck gun?

1. ## How do you determine the flow from an automatic nozzle on a deck gun?

The question came up the other night at driver operator class of how you know how much water you are flowing from an automatic nozzle on a deck gun. I asked do you have flow meters and they said no. We discussed how an automatic nozzle works and that throttling up just opens the baffle more to let more water out.

With a smooth bore nozzle and a pressure guage you can come close to knowing what the flow is. But with the automatic with no flow meter how do you know?

Help a brother out and tell me I am missing something obvious here.

Thanks,

FyredUp

2. Maybe possible to run off the tank or even setup a portable pond with known gallons. Time how long it takes to empty the tank. That will give you a "close" gpm.

3. And be sure to keep the automatics serviced so that the g/m doesn't change.

4. Okay thanks. Basically, even TFT is admitting that if you don't have flow meters or you haven't tested the flow with a smoothbore nozzle and then done calculations substituting the automatic nozzle there is no way to know what you are flowing.

Another reason to love automatic nozzles.

Give me a good old smoothbore on a deck gun anyday.

FyredUp

5. ## Backwards Hydraulics

The same process will work with master streams and handlines.

Discharge Pressure-Nozzle Pressure=Friction Loss

If you know the friction loss in the piping between the tip and the pump at various flow rates, you should be able to estimate the flow rate if you know the friction loss based on the above calculation.

If you are using a handline automatic, you need to divide the friction loss by the number of 100' segments of the hoseline to determine friction loss/100' and then work the math back to determine flow rate.

Hope that this helps.

6. hartin...

Again, by your post and previous ones, there is no way to determine flow without either having done prior testing on the piping or having flow meters.

With a smoothbore or a single gallonage nozzle you can come very close to the right pressure for the right gpm for that nozzle by either using the discharge gauge or the gauge on the gun itself.

Handlines are easy EP = NP + FL + SA +/- EL

It doesn;t matter what kind of nozzle as long as you add the right Nozzle pressure into the equation.

FyredUp

7. ## Absolutely Correct

Fyred Up,

You are absolutely correct. You need to work it out with a pitot tube and solid stream tip or flow meter and any nozzle with a known flow rate and pressure. Backwards hydraulics only works when yo know the variables.

Cheers

8. The TFT method is valid except for one point. The friction loss should not be determined by subtracting the Pitot pressure from the PDP. The Pitot pressure is a velocity pressure and the PDP is a “Normal” pressure (“Normal” in the physics sense - perpendicular to the pipe wall). A base of nozzle pressure should be used. The base of nozzle pressure is close to the Pitot pressure when the nozzle orifice is small (I.e., 1-Ľ” or less in diameter). However, when calibrating the monitor nozzle piping for flow rates and pressure drops, larger flows are needed and thus larger diameter nozzle orifices are needed (i.e., 2”). If the monitor nozzle does not have a base of nozzle gauge, I suggest using an in-line pressure gauge at the base of the nozzle or tapping a Ľ” hole at the base of the nozzle into which a pressure gauge can be attached. The gauges should be recently calibrated and of high accuracy (I.e., +/- 1% Full Scale).

I am puzzled by the TFT brochure for the Monsoon nozzle where it was stated that it will not “steal” water from hand lines. The nozzle can be operated from 300 gpm to 2,000 gpm. Consider a water supply that can deliver a maximum of 2,000 gpm. You are operating the Monsoon at 500 gpm and have other hand lines operating at 1,500 gpm (multiple hand lines, of course) for a grand total of 2,000 gpm. If you open the Mosoon to 2,000 gpm something bad will happen - cavitation of some pumps, “stealing” water (a bad term in its own right), or something else. What gives????

9. Originally Posted by hartin
Fyred Up,

You are absolutely correct. You need to work it out with a pitot tube and solid stream tip or flow meter and any nozzle with a known flow rate and pressure. Backwards hydraulics only works when yo know the variables.

Cheers
Can't you just use the rated flow of the nozzle? i.e. if it is a 1250 gpm nozzle at 100 psi, use 1250 (or whatever flow you want up to 1250) to compute your friction loss? some monitors make it even easier by having a gauge right behind the nozzle.

10. How do you know your 1250gpm nozzle is putting out 1250gpm?

11. I thought the question was for friction loss calculations.

12. MasterFF: Can't you just use the rated flow of the nozzle? i.e. if it is a 1250 gpm nozzle at 100 psi, use 1250 (or whatever flow you want up to 1250) to compute your friction loss? some monitors make it even easier by having a gauge right behind the nozzle.
The problem was and still remains this...IF you don't have a flow meter, OR, you haven't done flow tesating with a smooth bore and a pitot guage to know the friction loss for 1250 gpm, you have absolutely no way of knowing when that automatic nozzle reaches 1250 gpm. IF that nozzle operates at 100 psi and has a range of say 300 to 1250 you have no clue what is being flowed because in reality it could be anything within that range.

FyredUp

13. I think that your real problem is that even if you have flow tested your deck gun plumbing with a SB and a pitot, and even if you mantain your autos properly (*coughyeahrighcough*), your auto could be regulating by 5-10psi off of normal (I believe that NFPA allows a 10% deviation - that would mean that your MS auto could be regulating at 90psi one day and 110psi the next - 20psi margin - and you would never know the difference!).

Especially with a well-designed waterway, your deck gun plumbing should be pretty low friction loss, and 20psi could mean a pretty big difference in flow. Combine this with an electronic engine governor, which tries to maintain a pressure, not RPM, and you could be in a pretty bad situation.

We can debate handline nozzles all day, but the only applications that justify a fog tip on a master stream are prolonged exposure coverage/tank cooling, foam operations, or variable length bomb lines with portable monitors.

14. BlitzfireSolo: I think that your real problem is that even if you have flow tested your deck gun plumbing with a SB and a pitot, and even if you mantain your autos properly (*coughyeahrighcough*), your auto could be regulating by 5-10psi off of normal (I believe that NFPA allows a 10% deviation - that would mean that your MS auto could be regulating at 90psi one day and 110psi the next - 20psi margin - and you would never know the difference!).

Especially with a well-designed waterway, your deck gun plumbing should be pretty low friction loss, and 20psi could mean a pretty big difference in flow. Combine this with an electronic engine governor, which tries to maintain a pressure, not RPM, and you could be in a pretty bad situation.

We can debate handline nozzles all day, but the only applications that justify a fog tip on a master stream are prolonged exposure coverage/tank cooling, foam operations, or variable length bomb lines with portable monitors.
I couldn't possibly agree more with you about there being only certain special situations where a fog nozzle is a wise choice for a master stream. I want Quad stacked smoothbore tips on there and eventually we will have them.

We had a call the other night for an "out of control, controlled burn" of a structure being demolished. I thought heck let's blitz this thing while they establish a water supply. Even at what I know should have been more than adequate PDP the stream wasn't getting to the fire it was breaking up. We switched to a smoothbore tip from another rig and pounded the fire with that.

As for the deck gun plumbing it has only 2 slight bends in it to accomodate other plumbing near it I would guess they are 20 degrees a piece if that. It will flow over 1200 from draft through the deck gun we proved that with a pitot and smooth bores. we probably could have done more but were pulling a whirlpool at the strainer...we need to get a tether ball for that strainer!!

I will admit freely I am a smoothbore guy...both for handlines and master stream applications. Yet here we use low pressure fogs on handlines backed with a slug tip. Better than autos in my opinion, but still not a maintenance free smooth bore tip. Maybe some day...a guy can dream can't he?

FyredUp

15. To answer your original question, contact the manufacturer of the nozzle in question. I can tell that the Elkhart SM100 flows 1000gpm @ 100psi. At 90psi of discharge press. you will get 425gpm. Those numbers come from the back of their catalog. While the stream may look good, you are not getting the water you think you are. I like to call this "The fallacy of the Automatic Nozzle".

16. See, I thing auto nozzles are great for wagon pipes - just open the valve, and throttle up until you start to run out of water or hit redline.

I suppose it would be a good place for a flowmeter.

17. SBrooks,

You point out a very good reason why automatics are a unique tool that simplifies certain operations. I think the problem here is that even the advantages do not outweight the disadvantages.

If you had a flowmeter (you are right - an essential tool for this type of operation), and if you set your engine governor (if so equipped) to RPM mode, you would overcome the problems listed in this thread.

However, one of the biggest problems you see at stubborn defensive fires is that the master streams are evaporating before they even reach the seat of the fire, and are being lost in the thermal column. In this case, it makes no sense to apply a fog nozzle (even on straight stream - read: small droplets) when you could be applying a solid stream from a solid bore nozzle.

This is the same reason that I advocate 2,000gpm deck guns - not so much for the increased water, but so that you have a bigger, more solid stream of water actually reaching the seat of the fire.

To summarize, I totally agree with your logic, it's just that there are further disadvantages that I feel make the auto an inappropriate tool for most master stream operations.

18. I'm pretty well convinced that a fog nozzle on straight stream's flow is 'solid' after a few inches of leaving the nozzle. Plus, it's leaving at 100 psi vs. 80 psi, so the stream is moving faster. If the stream is evaporating prior to reaching the burning surface, you're not using enough water for the fire. An automatic nozzle, preferably a 2000 gpm automatic nozzle, can use every bit of pump and water supply you've got, up to 2000 gpm.

A smoothbore nozzle operation would require estimating how much water is available (which changes as other streams are put in service), what the friction loss is from the water supply to the nozzle, and then, while the line is shut down, choose the appropriate smoothbore size, and then start the stream. Repeat as necessary.

If you're not interested in maximizing flow, you can get away with one of the lower GPM smoothbores, but you won't be using all of your available water supply or pumping power - which means that you can 'eat' less heat output. You'll flow water until the fuel burns down to a manageable size.

Master streams aren't an operation used very often, especially maximum flow master streams - if they were you'd burn yourself out of a district. The simplest operation should prevail: Lay multiple big lines, aim nozzle, open discharge, throttle until you hit a limit. If you run out of water supply before you run out of pump or nozzle, lay another line. If you run out of nozzle first, put another in service. If you run out of pump, use two. Eventually, you'll run out of something, but you'll be flowing the most water you can.

Has anyone used a 'Vindicator' nozzle as a master stream device? It has a wider pressure / flow range than smoothbores, though not as wide as some automatic fog nozzles.

19. SBrooks,

All good points on the autos - I'm all for simplifying and speeding operations. I think we'd have to do a stream footprint and droplet size comparison to know for sure - I'd still be inclined to say that the SBs will have bigger droplets than the autos.

Also, regarding pressure: I have never bought into the 80psi max pressure for master stream smooth bores. I'll normally operate anywhere in the 80-115psi range, give or take - no problems with streams breaking up.

If the stream is evaporating prior to reaching the burning surface, you're not using enough water for the fire. An automatic nozzle, preferably a 2000 gpm automatic nozzle, can use every bit of pump and water supply you've got, up to 2000 gpm.
Couldn 't agree with you more on flow. See comment in my last post.

Heh, I was going to mention the Vindicator in my last post. Seen the Vindicator MS used first hand. Used the Vindicator handline series personally - we own several. Nice nozzles. Still, even though a Vindicator has bigger droplets than a fog, I would think the solid bore would have even bigger droplets. Hmm, how about a self-educting Vindicator for master stream foam ops....THAT would be nice.

What we really need is an automatic smoothbore - something that you could adjust the orifice size on to suit the flow at hand. That would be really nice!

20. What we really need is an automatic smoothbore - something that you could adjust the orifice size on to suit the flow at hand. That would be really nice!

Fog nozzles on straight stream are a convergent nozzle, smoothbores are a divergent nozzle. Ideally, for a smoothbore, you'd be able to suspend a 'BB' or teardrop shaped object just inside the orefice, such that, instead of of expanding, the stream will be collapsing on the vacuum behind the BB.

I've never even SEEN a vindicator nozzle in person. But I think that if you taped up the vents, you might just have something like that.

I've also thought that perhaps you could form a smoothbore nozzle out of silicone or something that would stretch at higher pressure, giving a larger orefice.

21. Vindicators are low pressure nozzles with an "optimum flow" rating but have a spring loaded "baffle" in them to allow more water output once you have exceeded the "rating". They break the water up much like the inside of combination nozzle and use air flow and a long barrel to create a "laminar flow" basically a fancy way of saying youre reshaping a broken stream.

There are 2 pictures looking into the barrel from both ends.

22. Originally Posted by SBrooks

I've also thought that perhaps you could form a smoothbore nozzle out of silicone or something that would stretch at higher pressure, giving a larger orefice.
There might be a shop in your area that sells those types of items in all different sizes and colors too

23. I should have seen that coming

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