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Question DetailsAsked on 7/10/2016

Sprinkler system repair you system needs bigger heads

The sprinkler heads are to small, not giving off enough water.

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1 Answer


IF you mean internal fire sprinkler system, a wide variety of flow rates, coverage areas, fogging or spray, out-cast or down-cast or specific coverage area (like paint locker) etc sprinkler heads are available - but it is necessary to run through the calculations to see if your system can provide the water necessary. Generally, a normal 1" supply pipe and 3/4" internal piping house hold system without fire booster pump can only handle about 1 to maybe 3 normal outcast (full 360 degree fan) sprinkler heads at one time.


If you mean a lawn sprinkler system, likely as that is the category this is listed under (though unknown if you or AL make that choice), there are three normal rough ranges of sprinkler heads in common use - the normal lawn heads rated for generally about 40-60 psi household supply operating pressure and about 1-3 gpm/head coming off 3/4" pipe on each branch, commercial sprinkler heads like golf courses and such commonly have ratings for about 50-100 psi and about 10-100 gpm and shooting usually 50-75 feet or so (though sometimes 100 or more radius) and normally coming off 1" to 2" pipe and generally with a booster pump on the system, and commercial farm sprinkler heads rated for up to 250 psi at times (generally around 100 psi plus or minus) and able to shoot up to 100 to over 200 feet or more, and commonly putting out 100-1500 gpm per head - usually coming off 4-6 inch pipe.

With your system, assuming normal lawn system, generally unless using fine mist heads only shooting a gasllon prer minute or less each (and only maybe 10-15 feet spray radius), in many cases about 3-4 spray heads on at a time (on each zone) is about the max for a system with 3/4" pipe running off normal household pressure - sometimes less in low pressure supply areas.

In each case, there are design tables showing the needed pressure and pipe sizes to operate a certain brand/model sprinkler, tables to figure losses due to pipe length or bends or valves and number of sprinkler heads of each type, etc. Generally speaking, unless a specific head was grossly not the proper rating for your system or is damaged, enlarging the head to provide more water will not fix your problem if low flow is the problem at multiple heads - usually the issue is inadequate supply piping size (either supply line to the house, supply line from meter to sprinkler timer box, or buried line size to the sprinklers), or just plain too low a line pressure due to too low a supply pressure, too much use by other demands lowering the pressure, too small a piping (too many loses in the line), too many sprinkler head on a branch, branches too long or too many bends, etc. Generally, for house hold sprinklers, unless you get special low-pressure heads (which typically have about a 10-20 foot max spray radius), you need about 30-40 psi in the sprinkler piping system (at the control box) when the system is in use - which may normally mean 40-70 psi static (no flow) line pressure to the control box with normal 3/4" lines.

You can check the website for your control valve and spray head manufacturer for design manual or tables, or Search the List for a Lawn Irrigation contractor or a Landscaper who also does irrigation system and installs who can evaluate your system and tell you if you have inflow volume/pressure issues, too small a piping or too many heads on each branch, too many branches operating at one (commonly not more than one spray head zone and one drip line should be operating at one time), wrong heads for system or what.

Course, if your system is hitting all the areas it should, just putting out low flow rate, the cheapest solution is changing the cycle timing to provide the amount of water needed per cycle - which might require a singificant increase in time per zone. Typically 2-4 hours per cycle per zone is a common time for normal summer watering, but of course depends on flow rate at the head, evaporation rates, how large an area the head is hitting, etc - very large coverage but very low flow rate (misting) heads sometimes take 4-8 hours per zone, where as high flow high pressure heads may only take an hour or less to give the desired typically 1/4 to 1" (commonly about 1/2 to 1" once or twice a week) of water per cycle. you can calculate the flow rate, but you need to put out straight edged shallow flat pan (not significantly sloping sides as that messes up the measurement) to see how much water is actually being put out in a specific amount of time.

Answered 4 years ago by LCD

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