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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. |
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#37 In building a new home in a development area, I've come into contact with a number of local agencies, including the local fire department. As a mechanical engineer, I like to think I have some background in fluid flow and that sort of thing, but the local department and I can't settle on a certain issue I'd like to put to you. Our hydrants are pressurized (in general) at about 60 PSI (and flow at about 750 GPM at that pressure), and have varying flow capacities. In pumping to a remote fire we want to maximize water flow to the site, and we have a few options: First, we can hook up the hydrant to the pumper at the 4.5" discharge with an adapter and a 6" cloth hose (soft suction). The pumper has upper limits of 1500 GPM and 150 PSI, and the 4" hose line we are feeding from the pumper has a pressure rating of 180 PSI. Second, we can connect a valve to the hydrant which allows direct flow from the hydrant to the 4" hose line. The valve permits diverting the water through the pumper to permit the pumper to boost the pressure of the hydrant to the 180 PSI of the hose line. In the third option we looked at, we can "fully dress" the hydrant by utilizing all the discharges on the hydrant (one 4.5", and the two 2.5" discharges), and feed them into the pumper and from there go to the hose line. The givens in the question are the flow rate and pressure of the hyrant, the test pressure of the supply hose, and the friction loss parameter of the hose. Friction loss is a function of the volume and pressure of the water being flowed and the length of the hose. The question is, given the flow capacity of the hydrant and friction loss of the hose, is there a hookup to the hydrant which maximizes the flow from the hydrant, or is the flow rate determined entirely by the capacity of the supply hose to carry the volume of water to the fire? Thanks for the help. We really appreciate any information you can provide, or an answer to our little riddle. There are a number of items here that don't add up.
> Our hydrants are pressurized (in general) at about 60 PSI (and flow at A hydrant flowing at 60 psi is going to be showing 1295 GPM when discharging through a 2½" outlet. Are you sure that this is a flow pressure? It sounds to me more like a static pressure.
> In pumping to a remote fire we want to maximize water flow to the site,
> First, we can hook up the hydrant to the pumper at the 4.5" discharge Engines are rated at 100% of their rated capacity at 150 psi, 70% at 200 psi and 50% at 250 psi so there is no upper limit of 150 psi. Large diameter hose should be service test rated at 300 working psi and 600 psi test, not 180 psi. I'm not sure where this hose came from but it doesn't sound NFPA compliant. > Second, we can connect a valve to the hydrant which allows direct flow I have no clue at to how long of a hose lay you are talking about or the required flow through the hose, but for general purposes a relay pressure of 150 psi is usually adequate.
> In the third option we looked at, we can "fully dress" the hydrant by That would be appropriate for hydrants with unusually low residual pressures where a significant loss is encountered in the hookup between the hydrant and the engine.
> The question is, given the flow capacity of the hydrant and friction Well, we don't really know the flow capacity of the hydrant. First you need to perform a correct industry standard test of the hydrant and determine through the Hazen-Williams formula what exactly the hydrant can produce. Then we need to know the length of the hose lay and any elevation issues. From there we can compute with reasonable accuracy what flows could be expected at the end of the lay either with or without boosting with an engine, and whether a standard steamer hookup to the hydrant would be sufficient or if the hose outlets should also be taken. Send me some data and I'll send you an answer.
":O) Willis Lamm, Water Supply Officer |
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#38 - The public water district has three fire hydrants in it's system is being asked by the board of fire commissioners to do annual flow tests on the hydrants. We can not get any real good information on this . These hydrants were flow tested in 1968 when system was installed and again in 1999. We would agree there should be policy as to the frequency, but not annually. Our question is are there any standards in place to specify flow testing requirements. --- water plant operator There are various standards published by the NFPA and listed by the Uniform Fire Code. There are two basic tenets with respect to hydrant testing. The first is a requirement that dry barrel hydrants be tested at least annually. The second is that for all practical purposes that requirement falls on the fire agency. The practical application is this. In the typical community the fire agency performs its annual inspection and testing of fire hydrants. The exact process varies by location but at minimum the hydrants are checked for operational function, visually inspected for damage, flushed, checked for proper valve operation, cap threads lubricated and where frost is an issue, verifying that the bodies drain properly. Since the hydrants are being flowed anyway, Many fire agencies perform a simple single outlet flow test typically using the same instruments that they use to perform their required annual service testing of their fire engines. In some instances, the water agencies prefer that the fire agencies use water agency instruments. The single outlet tests, if conducted properly, can be used as a basis for calculating the available hydrant flows and will meet the appropriate standards for testing and record keeping with a minimum of water flow and disruption. In some locales fire dept. hydrant testing is coordinated with annual water main flushing to make most efficient use of the water and minimize frequency of water customer complaints. In some locales the hydrants are flush tested every year (minimum flow only to ensure operational readiness) and are flow tested every 3 to 5 years. In conclusion, there are a number of local options available. My suggestion is to establish a reasonable and practical testing criteria to protect the water agency's interests (establishing appropriate dates and times, notification procedure, how to report problems, etc.) and let the fire agency take responsibility for testing, keeping required records, painting bodies and flow indicator color codes, etc. Here's an information sheet that may be helpful. http://www.firehydrant.org/info/ftest1.html Willis Lamm, Water Supply Officer |
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#39 - Your website is very unique and interesting! I work in the Insurance Department at a University in Missouri. Last year, during cold temperatures, a fire hydrant outside one of our buildings burst, causing over $3000 in damages to the building. The City is denying our claim for reimbursement, stating that it was "an Act of God". Are there some pre-winter maintenance requirements for hydrants? Also, is there an average "life span" for a fire hydrant? I am assuming that this hydrant was either very, very old or just was not prepped for winter. Any light you can shed on this topic would be very much appreciated! --- Insurance Analyst Although municipal indemnity varies from state to state, there are American Water Works Association (AWWA) and National Fire Protection Association (NFPA) standards that apply to testing, inspection and maintenance of fire hydrants. Unless the causing freeze was of unusual and unforeseeable ferocity and duration, I would think that the "act of God" defense is little more than a smoke screen. According to NFPA and AWWA standards, dry barrel hydrants are to be tested and inspected at least once annually. Part of the inspection and testing process involves ensuring that the drain system is working properly so that the hydrant body doesn't stand full of water all winter and cause the very problem that you experienced. I would ask for the inspection and maintenance records on that hydrant for the past five years and see if the city exercised reasonable care and due diligence. With respect to age, it's not unheard of for properly maintained hydrants to remain in service for over 100 years. Freeze failures are generally caused by (1) use of an improper design for the climate, (2) lack of inspection and maintenance, or (3) failure to repair a leaky valve that results in the hydrant body staying flooded with water. If we can be of any further help, please feel free to write.
Willis Lamm, Water Supply Officer |
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#40 - What is the definition of a wharf hydrant. In what code, standard or reference can the definition be found? A wharf hydrant, by definition, is a hydrant that is found on a wharf or pier. Due to the design of the structure, conventional hydrants with conventional buries are not feasible to install. Pipeage of sufficient diameter to meet the fire flow requirements of the facility is run underneath or alongside the wharf or pier structure and the hydrants are threaded onto risers. Typically the risers are 4" diameter. Wharf heads can have single or multiple outlets of various diameters.
During the late 1950s and early 1960s it was common for wharf heads to
be installed in residential areas that had small water mains and that
were situated in mild climates. Many can still be seen today even
though they are nowhere near wharves or piers.
In glancing at the NFPA specifications, there are numerous details on calculating flows and spacing of wharf hydrants but the standards assume the reader's general knowledge as to what a wharf head actually is. As I recall, IFSTA training manuals describe wharf hydrants. I've attached a photo of one to this message. Hope this information helps. Willis Lamm, Water Supply Officer Moraga-Orinda Fire District |
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#41 - Which type of fire hydrant usually used in most of the country (Pillar type or Underground type) and why ? --- from Oman We use pillar type hydrants. They are easier to access, faster to connect hoses to, and provide greater flows. In areas where hard freezing is not an issue, we tend to use "wet barrel" hydrants such as the ones shown in the link below. Wet barrel hydrants have all their working components above ground for ease of use, inspection and maintenance. Wet barrel hydrants are manufactured in the US, Asia and Denmark and bolt onto a standard 6 inch riser with a 6-hole flange. http://www.firehydrant.org/pictures/ebmud01.html This feature discusses hydrant designs in the East Bay Municipal Utility District (EBMUD) in California that serves over 1 million people in many cities including Oakland and Berkeley. Current manufacturers based on the EBMUD design include: AVK Model 24-71 Clow Model 5 Jones Model 40-40 Construction information can be found here: http://www.firehydrant.org/info/design01.html If I can be of any further assistance, please feel free to contact me.
Willis Lamm, Water Supply Officer |
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#42 - > We are currently preparing for an ISO review and do not have sufficient water supply to test all of our hydrants. Do you know of any system that can be used to limit water usage and still get fairly accurate results. Thanks for the help. I'm sorry but I'm a bit confused by the "sufficient water supply" part of your message. You don't turn on all the hydrants at one time to test them and for that matter, they all don't have to be tested on the same day / week / year, etc. The concept behind flow testing is to determine what each hydrant is capable of delivering during a fire. How long the hydrant will flow is simply a matter of calculating how much average storage you hold in your reservoirs. The standard test involves discharging from one 2½" outlet and taking readings. From those readings you can fairly accurately calculate what the total flow capacity of the hydrant would be if you were pumping from all outlets. Depending on how hot the system is, the actual water discharged during each test ranges from about 250 to 750 GPM. Here's our web document on flow testing. http://www.firehydrant.org/info/ftest1.html Water supply makes up 40% of your total ISO score. A little bit of preparation in this area can present a first class looking water supply system to the inspector. If you have any more questions please feel free to contact me. Willis Lamm, Water Supply Officer |
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