Maximum flow for supply hose?

[FatherPierce]

I know the friction loss formula, but is there a ceiling maximum flow for supply hose? A hydraulics buff tells me that 3" hose cannot flow more than 750 gpm at any time. Anyone care to dispute?

[chiefengineer11]

I know the friction loss formula, but is there a ceiling maximum flow for supply hose? A hydraulics buff tells me that 3" hose cannot flow more than 750 gpm at any time. Anyone care to dispute?
Hypothetically, I disagree. Do the math. When you run out of numbers, you're there. From a practical standpoint, it's another story. Even 750 is pushing.

Stay safe out there, everyone goes home!

[Fire304]

I concur with Chief, on paper you have to deal with the safe working pressure of the hose and the capacity of your pump vs the friction loss. In reality you'll come up short as curves/kinks, and roughness on the inside of the hose create a little more friction loss.

As to exceeding the flow rates, friction loss is exponential, the harder you try the more energy it takes to flow. At a certian point, assuming you have the pump to push the water this hard and the hose can take it, you'll actually boil the water in the hose with cavitation (I've seen this happen in a small line once, steam rolling off the coupling, too hot to touch with your hand, freaked me out).

In practical terms, once you get above 50psi/100feet loss you are becoming very inefficient, better to lay a 2nd line or use bigger hose.

[InsuranceLCRep]

I know the friction loss formula, but is there a ceiling maximum flow for supply hose? A hydraulics buff tells me that 3" hose cannot flow more than 750 gpm at any time. Anyone care to dispute?


How long is the hose? 1000' no way, 50' not a problem.:D

[RFDACM02]

CE11 is right on. We just hashed this out in another thread but here's a brief example:

If we can flow 1000 gpm from a 2" smoothbore tip we can flow much more through a 3" orifice. The only added issues will be friction loss to get the water there and the maximum pressure the hose is rated for.

Also once you know the max psi you need to know what your pump can do. If you need 225 psi to send 1000 gpm your 1000 gpm pump won't work as its maxed out at 165 psi. (not counting a positive supply).

There are many variables, the best answer is to go out and test the set up your really thinking about.

[Pelican631]

Here's a chart showing flow through 500 feet of various sized hoses for different pump pressures and a 1250 gpm pump:

http://radioetcetera.googlepages.com/FlowChart.jpg

Here is a link to some slides with the same plot but for different hose lengths:

Pump Flow Charts (http://radioetcetera.googlepages.com/FlowCharts.ppt)

According to the plots, you can get 750 gpm from 3" hose for a 100 foot length, but not a 200 foot length, at least with a 1250 gpm pump and the conditions stated above.

Note that these charts show the limitation of the 1250 gpm pump (50% of rated capacity at 250 psi, etc.). What I find interesting is that these charts indicate that there are situations where you can actually get more flow by using less pump pressure. Is that actually correct, or did I do something wrong when creating the charts?

Andy

[Ha11igan]

Remember that all the pump ratings are thrown out the window when supplied from a hydrant.

[Fire304]

Remember that all the pump ratings are thrown out the window when supplied from a hydrant.

Not true, you can actually test your pump to NFPA standards from a hydrant...

Your pump rating is a measure of how much work, or "boost" you can get out of the pump. All the tests are done with discharge pressure corrected to test pressure, so when drafting you take the suction value and convert it to negative psi. The test pressure of 150psi is corrected to zero vacuum on the intake, (and also is supposed to be corrected to sea level pressure but I've yet to see that done).

I recently had the pleasure of witnessing an acceptance test on a new 1500gpm pump, at the 150psi stage it was pulling 15 inches vaccum, that converts to roughly 7.5psi, so the pump pressure was 142.5psi, not 150.

Take the same pump and feed it with pressurized source which is capable of flowing 1500gpm with 20psi residule, you'd be able to boost the pressure to 170psi and still make 1500gpm. Since this is a new truck and its rated over capacity is at 165psi, you can actully make 1500gpm at 185psi. Above 185 the flow rates will begin to decline, or more correctly, it will not be able to increase the pump pressure w/o decreasing the flow rate.

Taken another way...,

A 1000gpm pump being fed by a 1500gpm pump would be able to flow 1500gpm* but only boost pressure about 50-75psi (I can't give you an accurate number since this is below the flow chart for a 1000gpm pump) over the incoming pressure, so if the incoming pressure was 100psi you might be able to get 175psi discharge, but no more as you are at your capacity.

*This assumes there is no hyrdaulic reason the pump could not flow 1500gpm, such as small intakes or lack of enough discharges causing too much turbulance at this flow rate.

A 1000gpm pump being fed by with 1000gpm at 100psi incoming pressure would be able to flow 1000gpm up to 265psi (assuming it was a newer over rated design).

A 1000gpm pump being fed 500gpm at 100psi incoming would be able to pump 500gpm at 350psi.

[Fire304]

It was bugging me, so I actually did the math and figured out that a 1000gpm pump can flow 1500gpm at 80psi.

[KuhShise]

I have a major problem with the graphs in (http://radioetcetera.googlepages.com/FlowCharts.ppt)
The designer was mixing the equations for maximum pump capacity at specified flows with the stated hose length and 20 psi relay pressure at the second engine.
For 100psi discharge pressure into 1000 ft of hose, with 20 psi residual at the relay engine, the flows should be approximately as follows:
2 1/2" - 180 gpm; 3" - 283 gpm; 4" - 565 gpm; 5" - 1095 gpm 6" - theoretically 1250gpm, but will probably approach 1450 gpm depending upon transfer case ratio and motor horsepower / torque curve. Since a gasoline engine has a much lower torque and HP curve at low rpm, by overloading it at low rpm we might not even make the 1250 gpm pump spec. at 69 psi.
When we reach the specified pump volume point of 1250 gpm @ 150 psi the following occurs. (still maintaining 20 psi at the relay engine)
2 1/2" - 228 gpm; 3" - 360 gpm; 4" - 721 gpm; 5" - 1250 gpm @ 124psi; 6" - 1250 gpm @ 69 psi
If we had unlimited engine horsepower & pump flow, the 5" could supply 1396 gpm and the 6" hose a whopping 2040 gpm. at the specified 150 psi discharge pressure.
This calculation at the design point of the engine (1250 gpm) should allow the optimum hose load to be calculated for the engine. Since the friction loss in 4" hose at 1250 gpm is about 39 psi per hundred, loading 4" hose in the bed of a 1250 gpm engine allows only a 300 ft lay before the pressure / volume specification is exceeded. 1250 and 1500 pumps should have as a minimum 5" hose or be capable of laying dual 4" lines for relay.
A 1500 gpm pump can deliver full volume from draft only about 900 ft through 5" supply line with 15 psi incoming at the second engine.
A 1750 gpm engine at 150 psi can supply full volume through 600 ft of 5" hose with 20 psi at the relay engine. The same engine @ 180 psi (max for LDH) will deliver about 1300 gpm a distance of 1400 ft through 5" hose. So a 1400 or 1500 ft load of 5" LDH might be a good match for a 1750 gpm engine. There are lots of other considerations like your department's normal length of lay or special target hazards that will influence the choice of hose and bed size.
All of the above calculations are ball-park calculations and will be affected by hose characteristics, pressures and pump piping. Changes in hose diameter cause friction loss changes proportional to the 4.87 power of the diameter. Slight changes in diameter can cause large changes in friction loss. These recommendations are for purposes of initiating discussion and further investigation of how hose loads and lays affect the performance of engines on the fireground. I highly recommend actual tests of layouts and engines before settling on any load or tactic for firefighting.
Kuh Shise Just an old German BSer.

[Fire304]

A 1500 gpm pump can deliver full volume from draft only about 900 ft through 5" supply line with 15 psi incoming at the second engine.
I'm not sure how you arrived at this number. By my calculations, a 1500gpm pump running at 200psi is capable of 1050gpm. With LDH we'd actually be running at 180, so the flow would be a little higher, but to keep it simple we'll assume 1050gpm.

5" has 6.3psi friction loss per 100 at 1000gpm, we'll round up to 7psi/100'

180psi-15psi give you 165psi working pressure

165psi/7psi per 100feet = 2300feet before the first relay pumper.

[TVFR9923]

When you refer to the max working pressure for LDH as being 180psi, what type are talking about? The old vinyl coated stuff that is pressure tested to 200psi, or the woven jacketed type that is tested to 300psi?

[KuhShise]

Fire 304:
I agree that at 1050 (70% point) the distance would be 2300 ft, but we were speaking of 1500 gpm at draft. You can't depend upon the 10% overdesign of a new engine simply because we don't know the age of the engine. It might be our EE-12 that is a 1979 Mack - Watrous and used hard. Additionally, from draft the suction side of the equation approaches the 14.7 psi below atmospheric. Therefore we can not use the 165 psi cited in the previous postings.
As to where I come up with the friction loss figures. I use a Polish Calculator or finger method for the fireground or when sitting around with time to contemplate, use this equation. Fl = K * Q * Q * L Where K is a constant for the size of hose. Q = flow in 100's of gpms. L = number of 100 ft joints of hose.
The finger method is very simple. Hold your left hand facing you (pinkie to the right) for 5 inch hose the pinkie value is 2,000 gpm. This means that each finger is worth 400 gpm. The friction loss will be the value of the digit, (thumb = 1, index = 2, middle = 3, etc) squared. thus for 5" hose at 1200 gpm we have the middle finger (3) squared or about 9 psi per hundred. Number the coupling of each section of hose as it is placed in the bed (chalk or soapstone) and all you need to do is check the coupling when you attach it to the discharge and you will know how much has been laid. So if we had #8 coupling attached, you would pump at 92 psi +/- elevation to achieve a flow of 1200 gpm. (72 + 20 +/- elev.) For actual calculation, The K factor for various hose diameters is as follows: 1" = 250, 1 1/2" = 30, 1 3/4 = 11, 2" = 5, 2 1/2 = 2.5, 3" = 1, 4" = 1/4, & 5" = 1/15.
Pinkie flows are as follows for various hoses. 2 1/2 = 250 gpm (each finger 50 gpm), 3" = 500 gpm (100 gpm each), 4" = 1,000 gpm (200 gpm each) and 5" as stated above 2,000 gpm or each finger is 400 gpm.

TVFR9923:
Good safety practice prevents you from running at the test pressure for working fires. The 180 represents that safety factor (10% down) Our SOP requires the pump operator to contact I.C. for permission to exceed 180 psi on LDH. This is to allow the I.C. to formulate a plan incase we get a rupture when approaching the annual test pressure on the fire ground.

Kuh Shise

[KuhShise]

FatherPierce:
As has been stated in other posts on this thread..There is no theoretical limit to the amount of flow through a given diameter of hose, but it can not exceed the ability of the pumper (both volume & pressure) nor the hose burst pressure. If we use100' of 3" hose with 2 1/2" couplings and limit ourselves to 250 psi. then max flow will be about 1500 gpm, but what we need to do this would be a 3,000 gpm engine (50% volume at 250 psi). One application of this might be for training, where 100 ft of 3" can be substituted for 1,500 ft of 5" hose. Thus pumper practice does not require laying and repacking 1500 ft of 5" hose. Proper placement of 3 practice engines (pump panels facing each other) with 100' joints of 3" between will allow each pump operator to observe the result of their throttle adjustments and pressure control devices.
Kuh Shise

[TVFR9923]

TVFR9923:
Good safety practice prevents you from running at the test pressure for working fires. The 180 represents that safety factor (10% down) Our SOP requires the pump operator to contact I.C. for permission to exceed 180 psi on LDH. This is to allow the I.C. to formulate a plan incase we get a rupture when approaching the annual test pressure on the fire ground.


Thanks KuhShise. I see 180 or 185psi a lot on here for LDH. I was currious to see what the reasoning was and type of hose was being used. We test ours to 300psi and will pump it to around 220psi to supply elevated streams on our aerials.


As for the original question, by my math, you can move 750gpm 250' through 3" hose at 150psi PDP and have 20psi at the next punper. I chose 150psi as that is the rated capacity at draft. As others have pointed out, if you are working off of a decent hydrant, you could get more.

[Fire304]

KuhShise, I was speaking in hypothetical terms, not specifically to a particular truck, especially not to one that might not pass a pump test.

1050 is a valid flow for even an older truck, if you draft 1050 through a 6" suction (which most 1500 trucks will use) and from a reasonable height, say 10 feet, your suction should not be much above 10inches (I just pump tested my 1500 pumper from 10 feet at 1500 I was drawing 17inches through 2 sections of hard suction, don't recall what the 70% test was, but it was less than 10). There is no fire pump on the market which can draft at -14.7 psi, that would be 29.92 inches which is a perfect vacuum. Fire pumps are rated 22 inches max (and part of your NFPA pump test is to pull 22 inches of vacuum on a dry pump). So at 10 inches you'd loose 5psi of discharge pressure, well within out comfortable "fudge" factor since we're rounding.

I ran the math and I agree with your limit of 1500gpm on 100' of 3", but man wouldn't that be something to see! I wonder if I can calculate heat gain from that much friction loss (close to 200psi loss in the 100') and wonder if we'd boil the water (which I've seen done in very small hose at high flows). I'm gonna ask my wife the physics major if she can figure out how we'd do that.

[KuhShise]

Fire304
Let's examine your example of a 10 ft. lift. Since water causes a pressure of 0.435 psi per foot of depth, the 10' lift requires a force of 4.35 Psi to get the water into the pump with zero flow. Now if we allow this pump to try to accelerate the water from zero speed on a pond to the velocity needed to bring the water up the suction tube (inertia) this takes additional force. We also have the friction losses in the 20 ft of hard sleeve. We also have losses from the turbulence in the strainer holes. Lastly, there is a loss generated at the point where the water enters the eye of the impeller. This 90 degree turn requires a speed up of the water from almost zero to a pretty fast pace following the curve of the impeller. In fact you can prove this quite easily by cavitating the pump. At 70 degrees, water has a vapor pressure of 0.36 psi. When you cavitate an engine pumping 70 degree water the inertia, friction loss and lift in the system must equal 14.7 - 0.36 or the pump will be working an additional 14.34 psi plus the discharge pressure of 150 psi or a total input to discharge of 164.34 psi. I know I changed the flow from 1050 gpm to 1500, but that was my premise in my first post. As for the heat energy from friction, this is rapidly carried away with the 1500 gpm that is flowing through the hose. It is so slight you will not be able to measure the temperature rise with normal measuring devices. The example you cite about small diameter hose becoming heated was most probably caused by high pump rpm and very low flow volume. We have experienced this many times over the years. My first introduction to this was using a 5 stage centrifugal pump for booster operations.(1966) This type of arrangement used a high pressure relief valve (800 psi) that discharged back to the tank. Pumping less than 800 psi rapidly heated the water when the nozzle wasn't open, even to the point where the nozzle man burned his hands when he finally opened the knob. The chief and foreman on the rig insisted the pump operator throttle up until the pressure was 800 psi to prevent damage to the pump due to cold water chilling it if water wasn't circulating and then the knob was opened. Incidentally a 1750 gpm pump is not capable of delivering full volume without two 6" suction tubes in the water. One from each side of the engine. You might want to refer to Warren Isman's "Pump Operators Handbook" and Larry Davis's Rural Firefighting Operations Book 2 for a lot more in depth information.
Incidentally, every one of my students over the past 25 years has operated a 3 engine relay through 50 ft of 3" line with relay volumes exceeding 1500 gpm. It is a good way to avoid laying and picking up huge quantities of LDH when practicing multiple engine relays.
Kuh Shise

[Fire304]

Hmmm, well I won't dive into the theoriticals, you seem very well versed in that, but I can tell you the calibrated vacuum gauge the tester brought with him said 17" at 1500gpm. I found my notes and at 1050 I was drawing 7inches. Again, this is from 10' draft and 2 sections of suction with a basket strainer on the end.

As to the 1750 pump, you can make 1750 with one 6" and one 3" on the aux intake port, a trick I learned while visiting my local dealer, they were testing a brand new truck and only had one draft port. They admitted however that there was no way to do a 2000gpm w/o 2 suctions.

[KuhShise]

That is correct. You only need about an additional 200 gpm to make up for the max volume in the 6" suction. There are some other things you can do under fire conditions. A portable trash pump connected to the auxilery intake is one solution. However, some pumps behave badly when the turbulence is introduced on the side where the 6" sleeve is connected. I have had much better luck by bringing the additional flow into the opposite side so that the flows are opposing each other thus helping to force the flow into the impeller eye. the reason that your test gauge is reading less vacuum is because it is connected at a point near the shaft and can't be reading the pressure directly in the impeller eye where the pressure is the lowest. Some people will insist that attaching a hose to a suction inlet while drafting will "Suck the hose flat" and shut off the water. This is not true. The hose will collapse (narrow) until the turbulence (read friction loss) in the last 6" or so equals the difference between the internal pressure of the pump and the atmospheric pressure. You should not do this with a poorly bonded inner hose liner, because the violent vibrations can rip the lining away from the inner jacket and plug the 2 1/2" intake. The big thing is that you might be able to get an additional hose line on the fire by putting a PP into the draft source and feed any gated intake on the drafting engine.

[Pelican631]

Sorry I somehow missed the activity in this thread.

There was definitely a big error in the charts, as there was a typo in a constant in the spreadsheet. I've updated them with the correct constant, but if I understand you correctly KuhShise, your concern was that I was mixing pump capacity specs with hose calculations. Please help me understand where I'm going wrong in doing that, and whether the charts as they are now (after being updated) are valid or not. The thing that really shocked me was that they seem to show that you can get more flow at reduced pump pressure under some conditions. That's counter-intuitive to me...is that correct, or am I messing things up? If you can put it into volts and amps, that would make it easier on my electrical engineer brain :)

Thanks in advance,

Andy

[KuhShise]

Andy:
The problem exists when the chart reaches the discontinuity point at the capacity of the engine. 1250 at 150 psi, 875 at 200 psi & 625 at 250 psi. There is also a second discontinuity that comes about where the maximum working pressures for LDH is reached. While 250 psi through double jacket 3" is quite acceptable, Most older LDH needs to be stopped at 180 psi +/-. We need a cut off pressure set for each type of hose and a maximum operating flow for each size of engine. There is a third controlling issue at pressures below the design point of 150 psi. Because pressure of a centrifugal pump is directly related to pump speed, (read RPM) then pressures lower than 150 cause the engine to operate at speeds where the horsepower ability is being lowered. (Read horsepower = constant x pressure x volume) Lowering pressure reduces HP requirements, but lower RPM is also lowering the engine horsepower. This is where careful consideration of the average lay (hose size and length) of the department, in considering a new engine should take the time to address the relationship between pump curves and engine horespower / torque curves. Some engines like Mack and Cat will have a marked advantage over Detroit and Cummins at the low rpm end. There will also be differences in performance between single and two stage pumps coupled to each type and model of powerplant. We have an older Pierce with the first large Cat ever installed by Pierce. This 1750 gpm single stage Watrous was tested at Pierce from draft. (2 sided draft connection with 6" hard sleeve) It was able to produce 2154 gpm at 135 psi. It is in a satellite station and 3rd due for our high value district. (2 mi response) It was designed to drop a portable hydrant and feed two 1250 gpm Mack attack engines through 5 to 6 joints of LDH from a very good hydrant system. The equation that you are using to develop the graphs should follow a modified Hazen - Williams formula where the 400 constant is replaced by one somewhere around 243 or 250. This will provide a fairly good estimate of friction loss in hose that has a significant diameter stretch factor. The equation that I use is this: Friction loss (Fl) is equal to constant (243) times Flow (Q) squared times Length of lay in 100's of feet. then divide this by the hose diameter raised to the fifth power. This will generate curves that are very near those in your graphs. This long winded expression can be reduced further to Fl = K * Q * Q if we combine all the things into K for 1 section of hose. K for 1" = 250, 1 1/2" = 30, 1 3/4 = 11, 2" = 5, 3"x 2 1/2 c = 1, 3 x 3"c = 0.8, 4" = 1/4, 5" = 1/15 & 6" = 1/30. All these numbers can be adjusted for each particular hose manufacturer, but since most engines do not have accurate gauges (+ / - 10 psi) calibration this method or even Kentucky Windage using the Polish hand calculator in a previous post above will be quite adequate on the fireground.
Hope this helps.

Kuh Shise

[Pelican631]

Ok thanks KuhShise, I think I'm with you for the most part. The charts were generated using a form of the Hazen-Williams equation (pick one out of a hat, they all come out with similar numbers), but were hard-limited by a pump derate curve of:

100% of rated flow @ 150 psi
70% of rated flow @ 200 psi
50% of rated flow @ 250 psi

So yes, the charts are attempting to show the interaction of two factors (friction loss and pump capacity). What seems counterintuitive to me is that there is a point where pumping more pressure actually decreases your flow because you're in the derate portion of the pump curve. Is that correct, or am I totally missing something?

Coincidentally, I just noticed where you're from...I had a chance to tour your main station a few months ago when I was out there on business...I left the station drooling! You guys have a great setup!

Andy

[KuhShise]

That is what I was trying to say in another manner. Match your hose load to your engine size. What you are seeing is the mismatch of hose diameter and length of lay interacting with the maximum capability of the pump. Thanks for the compliment on the station and equipment. Since you have been here, you understand the need to be self suffient. Calling in a mutual aid company for a 20 mile response (30 minutes from scramble to scene) is sometimes an exercise in futility. We do have very good relationship with our city fathers and our citizens who generously support our efforts.

Kuh Shise