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We would be delighted to try and obtain an answer to any questions you might have regarding fire hydrants, whether of a technical or general nature. Below are recent questions and answers from the FireHydrant.org mailbag. If you have a question, Email Us.
#25 - Hello,
I have a couple of questions;
- Do you know of any special flow tests, such as Simpson flow test or Hazen Willam? If so, where can I get detailed info about them?
- Are there any special standards the ISO or NFPA sets that all municipalities must follow for flow/flushing/fire flow testing?
Here's an information sheet:
Hydrants are to be inspected twice a year, flushed or tested at least once per year. For full ISO credit, full tests should be conducted annually, however in communities that are particularly difficult to test, and that have highly reliable water systems, some slack is sometimes given in this area.
If you have any additional questions, please feel free to write.
":O) Willis Lamm,
#26 - I've been wondering about the attached hydrant and it's ilk. This jumbo sized dry barrel sits next to a large factory. The hydrant was made in the 1960's.
Will a hydrant such as the one in the photo, with a 6 1/4" main valve opening, have the potential to flow more water than a 5 1/4" hydrant, when both hydrants are limited to just the two 2 1/2" outlets as pictured?
Under the right circumstances. Here's the deal.
In order to get good flows out of hose outlets you need to maintain the highest residual pressure possible. On higher pressure mains you can do that through some pretty small taps. (We have some older 8" mains which have 4" hydrant taps, but they are located at lower elevations and have great static and residual pressures, so we can get at least 2,010 GPM out of old double 2½ hydrants. (We place a 2½ to 4½ increaser on the outlet and lay LDH from them to the fire and they are on the bottom of my upgrade list because they work really well.)
In cases where the pressure gradient is less such as a factory complex where pressure is limited by the elevation of the water storage tank (.434 psi/ft x the elevation of the water in feet,) one needs to increase the diameter of the piping in order to achieve similar flows. The water under lower pressure won't move as fast so it has to move in a larger diameter.
In such cases one would increase the diameter of pipes, taps and risers to get the same amount of water to the outlets without seeing a significant drop in pressure due to friction loss, turbulence at the main valve, etc.
To get some idea what this all means, take some hypothetical readings and plug them into the hycalc program using the double 2½ hydrant as the model. Assume the residual and pitot to be within 10% of each other. (Keep the relationship the same for both, e.g., if you have the residual 10% higher in one calc, keep it 10% higher for the others.)
You might start with a static pressure of 60 and a residual of 50 / pitot of 45. Then calc with a residual of 40 / pitot of 36. Then 30 / 27. Then 20 / 18. You can demonstrate the importance of sustaining good residual pressures and its effect on available flow.
Your 6¼ main hydrant valve will be about 25% more efficient than the 5¼ valve. If the water main can sustain good flows but is under low pressure and GPM output is of significant importance, the 6¼ main hydrant valve design makes more sense. Plus if later the body is changed out to a steamer hydrant or a steamer section is inserted below the double 2½ segment, the bury, valve and riser assembly can accommodate good steamer flows without digging the whole mess up and replacing it.
":O) Willis Lamm,
#27 - I am working on a feature film and the production designer would like to paint a couple of fire hydrants up to look as if they are from the east coast of the U.S. Apparently, he has seen some fire hydrants that have been painted up to look like soldiers, colonial soldiers I think. I have searched and searched with no luck. Do you have any idea where I might find a picture of these elusive fire hydrants?
Although we don't have any images on hand, the year 1976 was noteworthy for many bicentennial theme hydrants; colonial soldiers, Uncle Sam, Betsy Ross, and the American flag are a few plausible paint schemes.
If you are wanting verisimilitude, such hydrants would work for any time frame from 1976 forward, as it appears that a few cities here and there have retained these decorated hydrants over the years, sometimes in a haphazard yet continuous fashion, as the tradition is neglected or abandoned, but then rediscovered or adopted in a neighboring town. These paint schemes are typically maintained by volunteers and fade rapidly with exposure to the elements. Our town's hydrants were briefly decorated in 1976, according to the water superintendent here, but have long since reverted back to the ordinary.
#28 - I have a urgent question for you, and appreciate if you could reply asap.
In Singapore, most of our hydrants are double-pillar (i.e. 2 outlets) type. My question is:
Will the flow rate of water (in GPM or m3/min) be the same when you open 1 or 2 outlets? My rationale is that "what goes in is what goes out" from the Law of Continuity from Hydraulics. Regardless opening 1 or 2 outlets, water from the mains will flow out - opening 2 outlets simply means each outlet now will let out 1/2 the flow rate from the outlet if only that outlet is opened.
If my rationale is correct, we could just open 1 outlet of the hydrant to fill the water tank in our pumpers. In other words, will the time taken to fill the water tank be the same when 1 or 2 outlets are opened?
Thanks a million and awaiting your swift reply, please.
Thank you for your interesting question. Your rationale is partially correct and I will explain.
In a majority of instances the provision of multiple outlets intends primarily to deal with friction losses in fire hoses that are laid from those hydrants to pumpers. For example, if in the US we were needing to get 400 GPM from a hydrant 300 feet away using a single 2½ inch outlet and hose, we would lose 90 psi in the layout once flowing 400 GPM. That would leave insufficient intake pressure at the pump to maintain the desired flow. If we laid two parallel lines from two outlets we would lose 30 psi in the layout leaving us plenty of intake pressure at 400 GPM. Thus taking advantage of multiple outlets when operating a pumper some distance away from the hydrant can be important.
When operating the pumper at the hydrant or when supplying it with large diameter hose, the differences stated above do not exist or are minimal.
When looking at a specific hydrant, there are construction designs and pressures that can have an effect on the efficiency of flow from a single outlet. You can run a simple test to determine whether or not your hydrants fall into this category.
Sample a few hydrants in your city. Pick different elevations where the static pressure in the system would be different. Connect the hose that you would normally use to fill your pumper but leave the discharge end of the hose disconnected so that there is no "back pressure". Just secure it so that it doesn't whip around and cause water damage and/or attach a diffuser basket to it. Place a cap gauge on the unused hydrant outlet, completely open the hydrant and note the pressure.
As a rule of thumb, if the residual pressure on the second outlet is greater than 20 psi while the first outlet is fully flowing, the design of that particular hydrant operating at your particular water main supply pressure will provide additional flow if you use both outlets.
Even in the above situations, for routine refilling of pumpers, this second outlet is probably not significant. When operating at a major fire where you need every drop you can get, it may make a difference. Bear in mind that restrictions and losses through the connected hoses play a part in all of this so your consideration of the hydraulic Law of Continuity with respect to the hydrant itself is not in error. We are simply going past theoretical hydraulics and delving into practical hydraulics.
If you want to take some measurements and convert them into English units, I have a small computer program that I wrote that can fairly accurately calculate (1) the discharge from a single outlet, (2) the available discharge if both outlets were flowed, and (3) a rough estimate of the capacity of the water main.
If this interests you I would be happy to provide you with the program and testing instructions (at no cost). The program is written in Basic and should run on any PC.
If you do experiment and take some readings from your system, I would be most interested in reading the results. Please also feel free to ask additional questions.
":O) Willis Lamm,
#29 - Hello, I am the Chief of a volunteer department in Pennsylvania. The water authority is installing a new ten inch water main to a industrial park that is presently not served with water. The new section of line will run approximately 2.5 miles through land that is presently farmland but is zoned for industrial use. My question is this. Where can I get supporting documentation as to hydrant spacing along this line? I have been through NFPA standards and I cannot find any standard that spells out any minimum spacing standards. I need this information urgently for the decision on where and how many hydrants will be made using a cost basis rather than public safety.
The actual statutory requirements for fire hydrants vary from state to state. Some states have adopted the Uniform Fire Code, some have adopted a locally amended version of the UFC, and some have not adopted the code. The Insurance Services Office (ISO) apply NFPA standards as well as the Uniform Fire Code when scoring local jurisdictions for establishing an agency's insurance protection class. Therefore as a practical matter, these are the guidelines that should be followed.
NFPA has published a table of distances. This table actually varies according to the hose loads carried by the local fire agency and falls into two general categories.
If your apparatus carries large diameter hose (4" or greater), the maximum distance from any fire hydrant to a protected structure shall not exceed the SHORTEST hose load of any of your designated in-service fire engines. (Reserve apparatus or special apparatus that do not ordinarily respond on a first alarm assignment as a pumping engine and that do not ordinarily carry full LDH loads, are usually exempted.)
Under ordinary circumstances the distance from hydrant to structure is measured to a functional location proximate to the building. In other words, if an engine would take a position in the street front of a structure that is set back 100 ft from the roadway, than the ISO inspector will usually measure from the hydrant to a reasonable point on the frontage. The additional distance ordinarily covered by attack lines would not be counted.
So if your shortest LDH hose load is 900 ft, then hydrants should be installed within 900 ft of all anticipated parcels with structures.
If you do not carry LDH on all of your first alarm engines, the Table of Distances starts discounting credit for all structures beyond 500 ft. of any hydrant and this discount increases with distance.
Another issue is total fire flow. A particular structure may require flows greater than one hydrant can provide. You can only get credit for flows from additional hydrants that are within the Table of Distances.
As a result of these and other practical issues, the prevailing spacing for fire hydrants is every 500 ft. alongside a public roadway, with additional hydrants installed as needed to serve structures that have significant setbacks from the public roadway and where engines would likely take positions in parking lots or private driveways. (These additional hydrants are typically the responsibility of the party who develops the parcel.)
While the agency I work for is in an urban environment, I live in a rural area with limited financial resources. We received a water system improvement grant to add water mains, but did not receive funds for fire hydrants. We mapped where hydrants would eventually be located and had taps and hydrant laterals installed at the time the water mains were put in. Then over successive years we were able to purchase hydrants and buries which we then had installed on the existing hydrant laterals. This approach significantly reduced our fire agency costs since we didn't have expenses associated with sawing up the roadway, trenching and repaving when the hydrants were installed.
The way I would probably approach your situation is this:
Part of my justification arguments would include:
Good luck with this project. Please let me know if I can be of further assistance.
":O) Willis Lamm, Water Supply Officer
#30 - I never knew this website existed! I'd like to know what agencies are involved in flushing fire hydrants in Orange County, CA. My agency is trying to get Best Management Practice (BMP) info. to all agencies involved with fire hydrant flushing/testing.
I'm not sure what Orange County is doing, but I can connect you with BMPs for the San Francisco Bay area, which is one of the most tightly controlled (if not the most tightly controlled) areas in the state for planned discharges of municipal water.
My agency operates under the East Bay Municipal Utility District's BMPs as they are quite comprehensive, yet relatively practical, and have withstood great scrutiny. The best person to contact to get EBMUD's most recent version of their flushing and flow testing BMPs is Jose Rios, PE, in EBMUD's Water Service Planning Division. Jose can be reached via email at firstname.lastname@example.org or by telephone at 510-287-1091.
If I can be of further assistance, please don't hesitate to contact me.
Willis Lamm, Water Supply Officer
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