valve_operation

ELECTRIC CONTROLLED IRRIGATION VALVES We will be discussing both Valve–in–Head sprinklers and Block System and how they operate. Essentially the operation of the valve in both systems is identical. A diaphragm controls the flow of water through the valve and sprinkler. It is either closed to stop the flow through the valve or the sprinkler, or in a raised position to allow water to bypass under it to irrigate the plant material. While most manufacturers build hydraulically controlled valves, most valves in a northern climate are controlled by electricity remotely from a control system. It is much more difficult to operate a hydraulically controlled valve in a freezing climate. ELECTRIC VALVE COMPONENTS 1. Diaphragm o seal which separates the “upper chamber” from the body of the valve o normally made of a rubber material 2. Upper Chamber o pressure is released or added to this area o causes the diaphragm to move up or down 3. Bonnet o the whole top assembly of the valve o it may include the diaphragm 4. Flow Control Stem o threaded shaft which limits the distance diaphragm can open o used to limit the amount of flow to balance a system o can be used to manually close a valve 5. Solenoid o coil of insulated wire which, when connected to a 24v AC current, creates an electromagnet o electromagnet lifts a plunger which opens the pressure by-pass port and allows pressure in the upper chamber to decrease 6. Plunger o small metal rubber tipped device which closes of the by-pass port 7. By-Pass Port o a small port that starts in the upper chamber and continues past the “plunger” and releases the water pressure into the outlet portion of the valve o the port is controlled by the opening and closing of the “plunger” 8. In-Take Port o small hole in middle of diaphragm that allows water pressure to build in the “upper chamber” o hole is often covered by a screen to prevent debris from entering upper chamber 9. Valve Inlet o water enters the valve from the water source into this section of the valve o the “diaphragm” stops the water at this point from leaving the valve o an angle valve will allow water to enter the bottom of the valve to facilitate water sources that are below the valve 10. Valve Outlet o after the “diaphragm” has opened, the water will leave the valve to provide flow to the sprinklers 11. Bleed (manual external) o small plug or stem that is attached to the upper chamber and is manually unthreaded o controls the release of water pressure from the upper chamber o this type of “manual bleed” generally exhausts water to the atmosphere 12. Bleed (manual internal) o controls the release of water pressure from the upper chamber o is activated by “turning” the solenoid assembly a quarter turn counter clockwise o manually lifts the plunger away from the by-pass port and allows water to escape to the “outlet” portion of the valve o water does not escape to the atmosphere GENERAL OPERATING PRINCIPLES A diaphragm valve is designed to take advantage of existing water pressure within the irrigation system. These valves are in a “normally closed” position, which means that when the valve is pressurized, it is closed. The diaphragm has equal pressure both underneath and above in the “upper chamber”. As the pressure is released from the upper chamber, an imbalance in pressure occurs and the diaphragm is forced to open from below. The water flow will move the diaphragm up and water will flow underneath and past the diaphragm and out the valve outlet. As a valve is activated from a remote location, electricity is sent to the solenoid creating an electromagnet that “pulls” the plunger away from the by-pass port. It is this action that allows the pressure from the upper chamber to escape and create the pressure imbalance. When the electricity is stopped the magnet releases the plunger and it will return to its original position effectively closing the “by-pass port”. Because water is continually flowing into the upper chamber through the small “inlet port” in the diaphragm, pressure will rebuild in the upper chamber once the by- pass port is closed. Valves are engineered to close at a preset slow speed to prevent water hammer from affecting the irrigation system. Both the inlet port and the upper chamber are carefully calibrated to govern the closing speed of the valve.