A pressure regulator's basic function is to maintain an irrigation system’s desired performance.
A drip irrigation system is made to take a set amount of water and apply constant pressure. The irrigation pressure regulator's role in this system is to maintain the desired performance. It works by limiting excessive incoming pressure to a constant outlet pressure.
Irrigation pressure regulators work by automatically adjusting their opening area based on the inlet pressure. The opening changes evenly to help assure the outlet pressure stays within acceptable limits.
A pressure regulator activates when water travels through the inlet end of the regulator and around the fixed seat. Water enters a hollow cylinder called a throttling stem (or t-stem). It is attached to a larger diaphragm near the outlet end. There is a spring around the t-stem that holds the flow area open and lets water through.
When water passes through at high pressures, the excess pressure acts on the diaphragm and forces the spring to compress. This ends up pushing the t-stem toward the seat. The opening near the seat closes just enough to maintain the desired pressure and flow. The balance between the force on the diaphragm and spring resistance creates the outlet pressure.
What does a pressure regulator do?
The water pressure regulator keeps the pressure within the system. It also protects against spikes or sudden drops in pressure from the water source. This device ensures the pressure within the system will stay consistent, thus resulting in optimal performance from the emitting devices.
Please note, various watering devices may specify they are “pressure compensating” however, this is different from pressure regulation. Compensation refers to an emitter always letting out the pre-set flow rate. This is regardless of small pressure changes. However, pressure compensating emitting devices will not regulate the system pressure.
Do you need a pressure regulator for drip irrigation?
Most if not all, pressurized irrigation systems will require a pressure regulator. An exception to this would be if you are using a gravity system with very low pressure, or very low flow. Pressure regulators do require sufficient flow to regulate the pressure. They need at least a 5 - 15 PSI differential between inlet pressure and regulating pressure.
How does a pressure regulator work?
Water flows through the inlet, around the seat and through the t-stem. Water pressure acting on the diaphragm forces the spring to compress, pushing the t-stem toward the seat. The closing of the area between the seat and the t-stem reduces the water pressure on the diaphragm. The balance between the force on the diaphragm and spring resistance make the outlet pressure.
Irrigation pressure regulators need outflow and back pressure to regulate the pressure within your irrigation system. With no water flowing through the regulator, the inlet and outlet pressures will read the same.
You will need to verify the pressure maintained in your system. Place a pressure gauge at the end of one zone. Turn the zone on and let it build pressure.
Once the lines have filled and emitters begin to flow then take the reading. This will reflect the working pressure within your system.
Because of this, a certain amount of pressure (PSI) and flow (GPH/GPM) is required for a pressure regulator to operate.
Adjustable vs. Preset
Another point is whether you want an adjustable water pressure regulator or a preset one.
Adjustable water pressure regulators for drip irrigation do exactly what their name sounds like. They let you adjust the PSI of the water flowing into your irrigation system.
For example, say you wanted the water pressure to be 25 PSI. Later you learned that was too high. You could simply lower the PSI on your regulator without needing to buy a new one.
The PSI on preset pressure regulators, on the other hand, are determined by the maker. If you wanted the water pressure in your system to be 25 PSI, you would need to buy a 25-PSI regulator. To adjust the pressure, you would need to remove one regulator and install one with a different set PSI (source).
Each type of regulator comes with pros and cons. Adjustable pressure regulators cost more upfront but offer much more flexibility. Presets can’t be adjusted but lower the risk of “user error”. A gardener can’t set the pressure too high or too low on accident.
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