Maximizing Efficiency with Sand Media Filters in Drip Irrigation Systems for Midwest Ag Growers

The Role of Sand Media Filters 

Sand media filters serve as the primary filtration method for NutraDrip. They remove debris and particulates from the water, ensuring that only clean water reaches the crops. The filtration process involves dirty water entering through the top manifold, passing through a sand bed where impurities are trapped, and exiting as clean water from the bottom manifold. 

How Sand Media Filters Work 

1. Filtration Process: 

• Dirty water enters the top manifold. 

• Water flows through the sand bed, where particles are trapped. 

• Clean water exits through the bottom manifold. 

• Pressure before and after the filter is monitored to determine when backflushing is necessary. 

1. Backflush Mechanism: 

• Triggered by a pressure differential, typically set between 5 and 9 PSI. 

• Clean water is used to backflush, running backward through the sand to remove trapped debris. 

• The system backflushes one tank at a time for 60-90 seconds each, ensuring thorough cleaning. 

1. Maintenance Checks: 

• Inspect the sand annually to ensure it is flowable and at the correct level. 

• Check the media level signature outside the tank to verify sand levels. 

• Ensure the backflush process lifts the sand properly by maintaining at least 25 pounds of pressure. 

Common Issues and Solutions 

Backflush Pressure 

• Issue: Filters may fail to maintain 25 pounds of bottom side pressure during backflush, leading to inadequate cleaning. 

Ex: The number one issue we see with sand media filters is the system will get into what we call a death spiral. This is where it can never clean itself and it just gets dirtier and dirtier. it tries to flush, does not have enough bottom side pressure, and it doesn’t ever get clean. This is what we would call a constant backflush cycle. 

• Solution: Check your flushing pressure during backflush since it’s a very important number to know. Depending on how your field is laid out, we may install a pressure sustaining, normally open valve (PSNO valve, this goes after your filter system that is normally open) to create back pressure during backflush, especially if the filter system is higher than the drip field. 

Backflush flow Requirements 

This process takes quite a bit of water during that back flush process to get that sand clean. 

• The 36-inch tanks require about 190 gallons a minute. 

• The 48-inch tanks require about 290 gallons a minute. 

Throttling Valve Adjustment 

• Issue: Backflush flow and pressure can be too aggressive, causing sand to be lost through the pipes.  

Ex: The drip field is much higher than the filter. NutraDrip has installed a system in Iowa where there is 90 pounds of pressure at the filter just to get 25 pounds of pressure to the top of the hill. When that grower goes to backflush, he’s got 90 pounds of pressure trying to lift this sand and if it’s too aggressive the sand is going to lift too much from pressure and go right out the backflush pipe. 

• Solution: A throttling valve on the backflush pipe regulates the water flow to prevent excessive water from being expelled during backflush.  

Typically, these valves are adjusted during installation and should remain set afterward. We can open the valve until a small amount of sand appears in the backflush water, then close it slightly until minimal or no sand is detected.  

 To check this, catch the backflush water with a bucket or in your hand, and observe for sand particles. It’s crucial to ensure the valve is open enough but not too much.  

In lower pressure systems, the valve can often be fully opened, but in systems with pressures above 30-35 pounds, careful adjustment and monitoring are essential. Proper setting of these valves is critical. 

Command Filter Maintenance 

• Issue: Plugged command filters or closed quarter turn valves can prevent backflush.  

This could be due to a problem with the command filter, located on the top manifold of both sand media and disc filters. The command filter is essential because it filters the water that activates the solenoids, which control the valves. If the command filter gets plugged or if the quarter-turn ball valve next to it is closed, the filters won’t flush, even if the controller is trying to initiate the process. 

• Solution: Ensure the quarter-turn valve remains open and regularly check and clean the command filter, ideally once a year, to ensure it stays clear and functional. If your filters aren’t flushing, this should be one of the first things to inspect. To verify valve operation, you can manually operate the solenoids by disconnecting the spaghetti tubes and flipping the solenoid to the open position. Water should flow, indicating the solenoid is working and moving the valve into the backflush stage. When returned to the closed or auto position, the water should vent, and the valve should revert to normal filtering operation. 

Additional Components and Safety Measures 

• Continuous Acting Air Vent: Ensures proper air release during operation. 

• Quick Relief Valve: Automatically releases excess pressure to prevent system damage, typically set at 65 pounds of pressure. 

Summary 

For agricultural growers in the Midwest, maintaining a reliable drip irrigation system is crucial for crop health and yield. Sand media filters are a vital component of these systems, ensuring that irrigation water remains clean and free from debris. By understanding the functionality of these filters and following best practices for maintenance, growers can prevent common issues, optimize water distribution, and safeguard their investment. Proper maintenance and regular checks will ensure that your drip irrigation system runs efficiently, supporting sustainable and productive farming in the Midwest.