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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 mailbag. If you have a question, Email Us.
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  • #49 - We are in a county where the water company will not allow fire hydrants nor the use of the water to fight fires. How could I find out the State law (Arkansas) or Federal law for allowing fire hydrants?

    Most codes and standards pertaining to water supply and fire hydrants are not mandated, but are voluntarily adopted by states and local jurisdictions. Unlike OSHA, for example, that has preemptive jurisdiction in all 50 states, the Uniform Fire Code has to be adopted by each state and/or in each jurisdiction within each state for it to apply.

    Obviously it is not appropriate for a water company to not allow water to be used for fire fighting purposes unless it is in such poor condition that to do so would unreasonably jeopardize water quality. Your state may have a law on the books that addresses this situation. Your State Fire Marshal's Office would be the agency most likely to know of any such law. The franchise agreement between your County and the water company may also shed some light on the situation.

    What oftentimes occurs is that water companies may be compelled to provide water for fire protection but are not required to install and maintain fire hydrants at the company's expense. In these instances other funds are found to pay for the hydrants and the fire department usually maintains them once installed. In my little rural California town, the Town Council managed to get a block grant to get a handful of hydrants installed. In another town in this county the water agency installed the hydrants and charged all the residents in the area served by those hydrants a small surcharge on their monthly water bills until the hydrants were paid for. In another community the town got a low interest public works loan for hydrants and repaid the loan through surcharges on the residents' tax bills.

    I'm aware of one situation where a private water company refused to discuss water for fire protection. The fire district petitioned the County to take over the water company through eminent domain for reasons of necessary public safety. This scared the water company into coming to the table and reaching a solution.

    Small water companies are often afraid of the liability and expense associated with fire hydrants. In such cases these fears can often be calmed by the fire agency agreeing to be responsible for everything past the isolation valve between the hydrant and the water main. Fire departments generally have strong immunity in the event a hydrant fails during a fire where in some states a water company may be found liable. Furthermore, banks are given incentives by the federal government to provide public agencies very low interest loans for public improvements which are not available to private utilities.

    All these issues need to be brought to the table so that you can design a win-win solution to your hydrant problems.

    If I can be of any further assistance please contact me.

    Willis Lamm, Water Supply Officer
    Moraga-Orinda (CA) Fire District

    #50 - I am a college student at Colorado College. This summer I am doing research for my physics department. I am trying to figure out if fire hydrants can ever be partially opened and if so, will the water coming out have a greater velocity? I am designing physics problems for everyone, and I think the fire hydrant aspect would be perfect! I was also curious if I could use one of your pictures to go along with the text problem. It would be so helpful if you could reply as soon as possible. I think your site is wonderful. I had a great time educating myself of the history and makings of fire hydrants. Plus, your pictures are spectacular. Thank you!

    Most or all modern (i.e. 1900) fire hydrants are a variation on a globe valve and you can use the throttling response data for a globe valve for a simulation of a the seating area of a hydrant (check publications of control valve data - Fischer Controls & others) Can hydrants be partially opened ? = Yes of course, not a good idea but it can be done.

    Will partially opening a hydrant increase the velocity of the discharge ? = No, of course not!! Think, all the flow has to pass thru the annular opening between the main valve and the seat. If the size of the annular opening is reduced less flow will pass thru (at a set differential pressure). The effect is pretty dramatic up until the height of the opening gets to about 25% of the seat diameter. The curve is almost asymptotic when the height of the annular opening is at 50% of the seat diameter

    The area of the outlet is fixed - The Flow is reduced when the hydrant is throttled - Therefore when the hydrant is throttled the velocity is reduced.


    I'm just a hydrant collector and don't know much about physics but wouldn't a partially open valve produce less volume of water but at a higher velocity? Wouldn't it be the same as when you put your thumb over the end of your garden hose to get it to spray with more velocity to wash your car?

    When you put you thumb over then end of a hose you reduce the area of the outlet - the outlet of a hyd is a fixed area. The question concerned the velocity OUT of a hydrant when the seat was restricted - The velocity in the seat area might well increase but the energy associated with the velocity increase will be wasted when the average velocity of the water is decreased as the water first turns a corner and then enters the hydrant barrel. To continue your garden hose analogy (not a bad analogy it incorporates all the principles) - When you put a nozzle on the end of your hoz you restrict the area and increase the velocity just like you said - You increase the 'reach' of your flow - And can get water all the way to the other side of the garden -


    Louis Carl, Senior Engineer, Kennedy Valve.

    #51 - NFPA 24 definition of private fire service mains is between the source of water and the base of the riser and the source of water and the base elbow of private fire hydrants. Would the source of water be the public main if this is the only source of water?

    In most cases a public main is the source of water for a private fire service main.

    Here's the deal.

    Generally speaking public mains and hydrants are in grids or are on dead ends that also have domestic water taps on them. The reason for this is that the water in these mains has to constantly circulate in order to remain sanitary. When a main serves only such things as sprinkler systems, standpipes and private hydrants, there isn't sufficient water circulation and the water becomes non-potable. Stale water cannot come in contact with the municipal water supply so it is kept separate by a one way check valve system which is generally considered the "source of water" under NFPA definitions.

    So in practicality, a majority of private mains are pretty much isolated systems that branch off the public systems, that are configured so that they can't accidentally contaminate the public system, and are typically maintained by the private property owner.

    Hope this answers your question.

    Willis Lamm, Water Supply Officer
    Moraga-Orinda Fire District

    #52 - Hi.... I am inquiring about some fire hydrants that we have on a National Park Service site in Marin County, California. We are proposing to replace several old fire hydrants with new ones. The park is requesting that the new fire hydrants look similar to the old ones. Do you know of any companies that manufacture a wet barrel fire hydrant that is similiar in appearance to the Greenberg Model 76 (see FHO #0513)? Thank you for your help in this matter!

    First of all, have you considered rebuilding your existing Model 76 hydrants? Parts are readily available for Greenbergs dated 1945 and newer. Here at the fire district we routinely rebuild Greenberg hydrants of your vintage and put them back out on the street to replace earlier obsolete models that don't have pumper outlets. Our experience has been that not only have we reduced our costs per hydrant from above $800 to less than $200, but the old Greenbergs were so well made they are outlasting some of the newer models that we also rebuild.

    How we do this is outlined in this feature:

    If you decide to consider this option there are a few "cores" laying about the region that you can use to get a few hydrants made up in advance. You could switch them for some of your park hydrants to rebuild so you don't have hydrants out of service for a long time, then you would end up with a few "spares" to cover losses due to vehicular damage or in case you need additional hydrants.

    Another option would be to rebuild the hydrants on site where they are. All the mechanical work could be done in place then a park painter could repaint them when the valve work is completed. That would reduce your costs even more.

    If you would prefer to pursue the new hydrant concept, Clow / Long Beach still makes somewhat of a "traditional" California Fire Hydrant. One is illustrated here, as image #0237

    ... and their catalog still shows a 3-outlet version that is comparable to the Greenberg Model 76.

    If you need additional information, please feel free to contact me.

    Willis Lamm, Water Supply Officer
    Moraga-Orinda Fire District

    #53 - We are looking for some type of locking devices, which use padlocks, to prevent casual use of hydrants. A local fire department had used some in the past put did not know where to order them. Do you have, or know where to look. The fire hydrants in use have the Iowa name on them.

    I don't believe that the padlock system is approved any more. Most agencies are switching to one of two types of devices that are relatively tamperproof but don't in any way impede fire department access to the hydrant or operating nut. One method employs a collar around the operating nut so that only a special socket type spanner (carried by the FD) will open the hydrant. The other approach involves installing tamper proof caps that only the fire department can remove.

    One of the more prolific vendors is Hydra-Shield. They have a website at

    Hope this information helps.

    Willis Lamm, Water Supply Officer
    Moraga-Orinda Fire District

    #54 - Do you know of any agencies or companies that have conducted test on the effects of water hammer of fire hydrants and water mains. Also what is the likelihood of a hydrant being turn off so quickly that a 4" cast-iron main, that is possibly 30 to 80 years old, bursts causing two holes the size of silver dollars on either side of the pipe. Any information would be appreciated

    Unlined cast iron mains were generally used until about 1943, so your main is probably around 70 years old or older. During World War II iron pipe was constructed of thinner material and lined with mortar to save iron for the war effort. This process also saved money, had less internal corrosion and was the conventional design until non-metalic pipe was produced in the mid 1950s. In some communities cast iron pipe was installed as late as the early 1960s. Post war pipe was generally of inferior quality and leaks are common.

    In some circumstances a hydrant can be shut down quickly enough to cause damaging water hammer. These are typically found on long dead end mains, especially in hill country. Typically water hammer damage results in an elbow separating somewhere down the dead end and typically the hydrant has to be on a 6" or larger diameter main to be moving enough water to generate the kinds of forces that will cause leaks.

    Small holes are usually corrosion related. Sometimes they can appear when a hydrant is flushed and internal encrustation (which is about all that was holding the weak spot together) is flushed away. In these incidents the flushing of the hydrant merely precipitated a failure that was bound to eventually present itself. I recommend annual flow testing of hydrants on weak mains with testing taking place on Monday or Tuesday mornings so if a leak does develop it doesn't have to be repaired over a weekend. This schedule actually does the water company a favor as statistically most leaks occur on nights and weekends when repair crews are on overtime. If failing spots can be revealed during the morning hours on week days repairs can be made much more economically.

    Aside from all of this it always makes sense to close hydrants slowly. Even on modern water main systems with new pipes, residents may have old piping and we don't need to unnecessarily start a leak in someone's wall or basement by spiking the main pressure by 30 or 40 pounds with a quick hydrant shutdown.

    Hope this information helps.

    Willis Lamm, Water Supply Officer
    Moraga-Orinda (CA) Fire District

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