U. S. Department of Agriculture NE-ENG-76

Natural Resources Conservation Service 10/93

**DRY HYDRANT DESIGN**

  --------------- -------------------------------------------------------
  NAME                 

  --------------- -------------------------------------------------------

  ---- ------------------- ----------- ----------- -------------- ---------
  A.   The depth from the                                         
       normal water level                                         
       to the inlet will                                          
       be at least                                                

       The total of:                               Ice Depth      3 ft.

       +Net annual                                                     
       evaporation (see                                           
       EFH NE 2-4g)\*                                             

       +Minimum fire use\*                                             

       +Other consumptive                                              
       use                                                        

       **\* not less than              Total Depth                3
       2.0 feet**                      of Intake =                
  ---- ------------------- ----------- ----------- -------------- ---------

  ---- ------------------------------- -------------------------- ---------
  B.   Determine the difference in                                
       elevation (static head or SHL)                             
       between the intake strainer and                            
       the suction inlet of the pump.                             
       Check with the local fire                                  
       department on the height of the                            
       suction inlets of their pumper                             
       units above the road surface.                              

                                       Use SHL =                       
  ---- ------------------------------- -------------------------- ---------

  ---- -------------------------------------------- ------------ ---------
  C.   Determine the design capacity for the                     
       system. Check with the local fire department              
       on their requirements.                                    

       Design for                                                gpm
  ---- -------------------------------------------- ------------ ---------

  ---- ------------------------------- -------------------------- ---------
  D.   Determine the intake strainer                              
       and standpipe losses (ISL). Use                            
       1.2 for 250 gpm, 4.8 for 500                               
       gpm, and 10.8 for 750 gpm.                                 

                                       ISL =                           
  ---- ------------------------------- -------------------------- ---------

  ---- ------------------------------------------------------------------
  E.   Determine the length of pipe needed from the standpipe to the
       intake strainer. Also determine the number of elbows and fittings
       required.

  ---- ------------------------------------------------------------------

  ---- ---- ------------- ------------ --- -------- --- --------- ------ ------ --- -- -------- --------- --- ------- ------ --- ------- ----- ---------
  F.        Determine the                                                                                                                      
            hydraulic                                                                                                                          
            head losses                                                                                                                        
            in the piping                                                                                                                      
            (PHL):                                                                                                                             

            Pipe diameter                                                                                                                      inches
            =                                                                                                                                  

            Pipe length =                                                                                                                      feet

            90 degree                                             @ 20                                        0                                feet
            elbows -                                              feet =                                                                       

            30/45 degree                                          @ 10                                        0                                feet
            elbows -                                              feet =                                                                       

            Reducers -                                                   @ 10                             0                                    feet
                                                                         feet =                                                                

                          L = Total                                                                       0                                    feet
                          equivalent                                                                                                           
                          pipe length                                                                                                          
                          =                                                                                                                    

                                                                                                                                               

            Determine the                                                                                                                      
            pipe loss                                                                                                                          
            coefficient                                                                                                                        
            (k):                                                                                                                               

                                           Values                                                                                              
                                           of k for                                                                                            
                                           100 feet                                                                                            
                                           of pipe                                                                                             

            Pipe Diameter                  For 250                                     For 500                                   For 750       
                                           gpm                                         gpm                                       gpm           

                                                                                                                                               

            6 inch                         0.5852                                      2.3408                                    5.267         

            8 inch                         0.1257                                      0.5027                                    1.131         

            10 inch                        0.0382                                      0.1530                                    0.344         

            12 inch                        0.0145                                      0.0578                                    0.130         

            PHL = L x (k                            0                           x (                                   / 100)             0.0   
            /100) =                                                                                                   =                        
  ---- ---- ------------- ------------ --- -------- --- --------- ------ ------ --- -- -------- --------- --- ------- ------ --- ------- ----- ---------

  ---- ----------------- ------------------------ ------- ---- ------- ---- ------- --- ------- --
  G.   Determine the                                                                            
       total hydraulic                                                                          
       head of the                                                                              
       system (H):                                                                              

                         H = SHL + ISL + PHL =    0.00    \+   0.00    \+   0.000   =   0.00    

       The total head of                                                                        
       the system (H)                                                                           
       must not be more                                                                         
       than 22 feet, the                                                                        
       maximum                                                                                  

       hydraulically                                                                            
       possible. It is                                                                          
       recommended that                                                                         
       this total head                                                                          
       be less than 20                                                                          
       feet,                                                                                    

       15 feet                                                                                  
       preferred.                                                                               

                                                                                                

       If H is                                                                                  
       excessive,                                                                               
       increase the size                                                                        
       of the pipe and                                                                          
       redesign.                                                                                

                                                                                                

  H.   See back for                                                                             
       other design                                                                             
       considerations.                                                                          
  ---- ----------------- ------------------------ ------- ---- ------- ---- ------- --- ------- --

A dry hydrant is a standpipe to which the local fire department can
attach its pumper unit and provide a minimum of 250 gallons of water per
minute. The dry hydrant connects to a water supply by underground
piping. The dry hydrant must be located near an all-weather road, easily
identified, and must be fitted with a standpipe connection compatible
with the hose connections used by the local fire department. The water
supply must be available when needed, whether during drought periods or
freezing weather.

**[Do you have an adequate water source and supply?]{.underline}** The
body of water should maintain its water level all year round without
excessive seepage or evaporation. In Nebraska, the lake or pond must be
at least 9 feet deep (below normal water line, with at least 7 feet of
water above (see NE-ENG-75) which provides an allowance for ice and
evaporation. However, where net evaporation exceeds 24 inches per year
(see EFH NE 2-4g), the additional evaporation must be accounted for.
Also, if the permanent pool is used for other purposes (irrigation or
livestock water), these consumptive uses must also be accounted for.

**[Where should the standpipe be located?]{.underline}** The standpipe
should be adjacent to an all-weather road/lane and accessible from an
all-weather public road so that the standpipe is accessible to a pumper
truck. The discharge of the standpipe should be 24 inches above the
ground, but the elevation does not have to match the pump inlet pipe on
the truck. It should project horizontally toward the road with a steamer
nozzle matching the local fire department\'s hard suction hose size and
thread types. A post and/or marker should be placed near the standpipe
for easy identification under inclement weather conditions and as a
protective measure.

Property near a dry hydrant may become eligible for fire ratings and
insurance costs well below that for property more distant from a water
supply for firefighting. Criteria used by the National Fire Protection
Association (NFPA) for an acceptable water source are:

1.  A water supply capable of supplying a minimum of 250 gallons per
    minute for 2 hours, or a minimum of 4,000 cubic feet.

2.  A water supply at least 2 feet deep over the intake strainer and
    available during a 50-year frequency drought or freeze.

3.  A maximum hydraulic lift, including losses due to the size and
    length of pipe required for installation, equal to 20 feet, 15 feet
    preferred.

**[Where should the intake strainer be located?]{.underline}** The top
of the intake strainer must be at least 7 feet below normal water line
(or maximum drawdown for other uses if lower), and must be at least 2
feet below the usable water level. The bottom of the pond must be 2 feet
or more below the bottom of the intake strainer, or a sump 2-feet deep
should be created below it to limit clogging by sediment. A 12-inch
minimum thickness of clean coarse gravel can be placed around the intake
strainer to further limit the clogging potential and prevent damage to
the strainer.

**[Where is the intake pipe placed?]{.underline}** The intake pipe (the
pipe between the intake strainer and the standpipe) should be as
straight as possible with a minimum number of bends and elbows. All pipe
below the pond normal water elevation must also be below the maximum
soil frost penetration depth.