Opening And Closing Pressure Control Valves

Pressure control valves are hydraulic valves fitted with a pilot valve and is used to regulate pressure and flow. The pilot valve is a device that regulates the pressure inside the hydraulic valves.

These valves are controlled by a 3-way valve. The 3-way valve is marked Open, Close and Auto. To open the pressure, simply turn the dial to Open and to close the valve, turn the dial to Close. To regulate the pressure, or for other automated functions, turn the dial to Auto. Keep in mind that turning the dial to open could burst a pipe because of high pressure. The pilot should be adjusted by the supervisor or manager. Some valves are fitted with pressure points. See section 6 of this chapter for more information on the use of these pressure points.

Hydraulic, gate or butterfly valves are used as infield valves. To open a gate valve, turn the wheel anticlockwise and to close the valve, turn the wheel clockwise.

Butterfly valves are equipped with a handle. To open the valve, turn the handle until it is in line with the pipe. To close the valve, turn the handle until it is perpendicular to the pipe. Some butterfly valves are equipped with a wheel and dial. When the wheel is turned, the dial indicates if it is opening or closing.

To set the flow rate for an irrigation block, the pressure needs to be adjusted by opening or closing the valve. To reduce the pressure, close the valve more, and to increase the pressure, open the valve more. All valves under water pressure must always be opened and closed very slowly to prevent water hammer and the resulting damage. See section 6 for the measuring and regulating of the pressure.

Regulating Infield Valve Pressure

It is very important that the pressure on infield valves is regulated properly and set to the required levels, as the pressure determines the flow rate for the irrigation block. If the pressure is too low, too little water will be delivered to the crops, resulting in water-stress that can impact negatively on the yield. If the pressure is too high, too much water will be delivered to the crops, which not only will result in water wastage, but also tend to make emitters mist. Misting causes emitters to spray water into the rows between the crops, and not on the root-zone.

The correct pressure levels for infield valves are determined and prescribed by the irrigation manager or supervisor. The supervisor or manager will also set the pilot valves that are used on hydraulic valves, and no other person should be allowed to adjust the settings.

Infield valves are located on valve risers or valve clusters. Usually, these risers consist of riser pipes, a valve (hydraulic, gate, butterfly) and either hydromatics or pressure points. A hydromatic is type of quick coupler that is used for pressure readings.

The hydromatic and pressure points are used to measure the pressure. To measure the pressure using the hydromatic:

• Fit a pressure gauge to a pipette, which fits into the hydromatic, and not to be confused with a pipette that it used in chemistry
• Insert the pipette with the gauge into the hydromatic
• Make sure the latch on the pipette locks on to the hydromatic
• The pressure will register on the gauge
• To release the pipette, push it down, unlock the latch and remove it

Example of Pipette and Hydromatic

To use the pressure point, the gauge must be fitted with a special needle. To take a pressure reading:

• Insert the needle carefully into the pressure point, as carelessness can damage the silicon nipple inside the pressure point.
• The pressure will register on the gauge.
• Remove the gauge by simply pulling the needle out of the pressure point. Be careful when inserting the needle.

Pressure Point and Gauge with Needle

Where a hydraulic valve is used, the pilot valve is set to regulate the pressure for the irrigation block. It is good practise to take a reading once the valve is open and the pressure is stable, around 10-20 minutes after opening. The norm is 1.8 to 2.3bar where micro emitters are used, but can vary depending on the characteristics of the block. It is however important to note that if the pilot valve is set to for example 2bar, the reading should not be lower than 1.8bar or higher than 2.2bar, which is a 10% tolerance. If the reading is outside this range, it must be reported to the supervisor or manager.

Where a gate or butterfly valve is used, the pressure must be set manually. Insert the gauge into the riser and open the valve slowly. Once the lateral lines in the block have filled with water and the pressure has stabilised, regulate the pressure by turning the wheel, thereby opening and closing the valve. If the required pressure is for example 2bar, and the reading on the gauge is 1.7bar, open the valve slowly until the pressure is 2bar. If the reading is 2.3bar, close the valve slowly until the reading is 2bar.

Measuring Infield Filter Pressure

In some irrigation systems, secondary inline filters are fitted. Using the same techniques as for the valves, measure the pressure upstream, being before the filter, and downstream, and being after the filter. The difference between the two readings should not be more than 0.5bar.

If the inline filters are in a bank, i.e. two or more filters are in parallel, the filters can be back-flushed. After back-flushing, take a pressure reading again. If the difference is still greater than 0.5 bar.

• Close the filter inlet valve
• Remove the filter lid
• Remove the elements from the filter
• Clean it with a brush (see the manual for the specific filter)
• Re-insert the elements
• Replace the filter lid
• Open the inlet valve

Take a pressure reading again. If the difference is still larger than 0.5 bar, report this to the supervisor or manager.