Lawn Irrigation Systems Are Classified As “Inline” Or “Anti-Siphon.”
In an inline system, valves are installed in line with the underground supply pipe or tubing, so they are installed underground. Inline valves control or block flow by means of a mechanical obstruction activated manually or electronically. They can be installed just about anywhere in the landscape without creating a visual nuisance.
In an anti-siphon system, valves are installed above ground either where a supply line exits a structure or on an underground supply line that loops up out of the ground in an inconspicuous location. Anti-siphon valves work by imposing an air gap to prevent siphonage whenever a backflow condition is present. Above-grade installation precludes the danger of submersion and provides more convenient access for maintenance and repair.
Lawn Sprinkler System Valves Categorized By Use:
Isolation Valve: Isolates the irrigation system from the main water supply when closed. When this valve is open, water from the main supply line enters the irrigation system. The isolation valve is closed for winterization. In an in-line irrigation system, this valve is usually located underground near the meter. In an above-ground system, it is usually located indoors or above ground near the point where the main water line exits a structure (usually a basement or garage).
Backflow Prevention Device: A valve or valves in a configuration for the purpose of preventing water that has entered the irrigation system from flowing back into the potable water system. In terms of health and safety, this is the most critical component of any lawn sprinkler system. Whether above or below ground, this unit is installed just downstream from the isolation valve.
Automatic Zone Control Valve: A valve connected to a timer/controller that controls the flow of water to a zone of sprinkler heads and drip emitters. Inline zone control valves are installed in a valve box below grade. Anti-siphon control valves are installed above ground in an inconspicuous location.
Lateral Line Drain Valve: A simple valve installed at the downstream ends and low spots in a system to drain lateral lines after each use.
Lawn Sprinkler System Valves: Identification
Valves are identified by their size, inlet connection type, outlet connection type (if different), and mechanism. (Example: 1″ NPT ball valve).
Mechanism Types Include:
Ball Valve: Is OPEN when a sphere with one hole bored through the center aligns with the inlet and CLOSED when the quarter-turn handle turns the ball and the hole perpendicular to the inlet.
Gate Valve: Is OPEN when a disk-shaped “gate” is drawn up out of the water pathway and CLOSED when the handle is rotated clockwise several times lowering the gate into the pathway.
Check Valve: A disk is seated on a seal at a forty-five degree angle to horizontal. Water flowing in the normal direction pushes the disk upward allowing flow. Water backflowing pushes the disk down against the seat stopping the flow.
Automatic Valve: A solenoid opens the valve automatically at times and intervals programmed into the system controller.
Connection Types Commonly Found On Inline Underground Irrigation System Valves Include:
FPT: Female Threaded. Also sometimes called FIP
MPT: Male Threaded. Also sometimes called MIP.
NPT: National Pipe Thread.
S (or Slip): Straight, smooth female connector receives pipe or “street” (male) fitting. Metal slip connections are soldered or brazed; plastic connections are glued. Also called “Sweat” (or Swt) on metal fittings that are to be soldered rather than threaded.
Barb: Male connector with barbs that slip inside pipe or tubing and are held in place by stainless steel crimp clamps. (Not used for BPD)
Union: A two-piece threaded connector usually installed in pairs so that whatever is between them can easily be disconnected. When installed, the inlet and outlet of each union are permanently connected to pipe or a valve. A captured nut on one piece is joined and tightened to the second piece completing a connection.
PVC: An abbreviated form of the term Schedule-40 PVC pipe. Lighter PVC can often be used for supply lines downstream of the zone control valves, but for the valve installations explained here, PVC means Schedule-40.
Solenoid: an electro-magnetic device consisting of wire wrapped around a core that produces a magnetic field when activated. In irrigation applications it opens automatic lawn sprinkler system valves when activated by the system controller.
Glue: a commonly used misnomer for solvent cement. To “glue” a plastic joint means to use either one-step “green” solvent cement or primer and regular solvent cement. The solvent cement looks and spreads like glue but reacts chemically with the plastic causing it to soften or melt slightly so a hub and pipe meld together.
Thread Tape: is a very thin non-adhesive tape used to make threaded connections. It provides a very satisfactory waterproof seal for tapered-thread joints when applied correctly. The Teflon reduces friction so that the threads can be made up tightly, and then it fills tiny gaps by expansion. Half-inch width works best for most lawn irrigation applications. Wrap the tape clockwise beginning one-half the width of the tape from the end of the male threads. On the first wrap, wrap down to the end of the threads, then begin wrapping upward to cover the loose end. Keep the tape flat. Don’t allow the tape to extend off the threads at the end of the pipe. Keep just enough tension on the tape while wrapping to cause the tape to stretch tightly into the threads without breaking. Overlap each wrap by fifty percent. Add a final wrap at the top of the threads directly over the previous wrap, and then hold the tape tightly against the threads with one finger while pulling to break the tape. Well-taped threads will look almost like they were painted white.
Thread Sealant Compound: is easier to apply and more forgiving than teflon tape. Look for a brand that’s impregnated with teflon for best friction reduction. Thread sealant compound works well with brass, copper, and PVC, but any excess that squeezes into the pipe or fitting should be removed by hand. Do not depend on flushing the system to get rid of the excess. Compounds can clog valves if left in the pipe. Other types of plastic can be damaged by the solvents in thread sealant compound. Use the tape when either part of the connection is polybutelene, ABS, or any plastic other than PVC.