Low pressure in a sprinkler system is frustrating for homeowners because it results in poor spray distance and incomplete coverage, leading to dry patches across the lawn. Diagnosing the issue requires a methodical approach, starting from the water source and moving through the system’s components. Understanding where the pressure drop is occurring is the first step toward restoring proper function.
Checking the Water Source and Main Components
The pressure entering your home’s plumbing dictates the maximum pressure available to the sprinkler system. If the water pressure is low everywhere—at indoor faucets and outdoor spigots—the issue may stem from municipal supply fluctuations or work being done on the main water line outside your property. Homeowners should first ensure the main water shutoff valve is completely open, as a partially closed valve restricts the overall volume and pressure.
Immediately following the main shutoff, the Backflow Prevention Device (BPD) or Pressure Vacuum Breaker (PVB) is a frequent site for flow restriction. These devices contain internal mechanisms designed to prevent irrigation water from entering the potable water supply. Fine debris, like sand or sediment, often collects within these mechanisms or their screens, physically narrowing the passage and causing a measurable pressure drop across the entire system.
If your system includes a Pressure Reducing Valve (PRV), this component manages the maximum downstream pressure. These regulators can fail over time, often sticking at a lower pressure setting than intended, or the initial factory setting may simply be too low for the system’s design. Checking the operational pressure setting on the PRV, usually between 40 and 60 pounds per square inch (psi), is necessary to rule out an incorrect or malfunctioning regulator.
Flow Restriction from Internal Obstructions
Once the main supply is confirmed, attention shifts to internal blockages that restrict flow within specific sections of the system. Control valves that direct water to different zones often contain small screen filters designed to catch sediment before it enters the distribution lines. These filters, along with the narrow internal passages of the solenoid valves themselves, can become clogged with mineral deposits or fine particles, preventing the valve from opening fully and starving the zone of adequate water volume.
The most common cause of localized low pressure is obstruction at the point of emission—the sprinkler head or nozzle. Over time, tiny pieces of grit, soil, or even small insects can become lodged in the precision-cut orifices of the nozzle. Simply removing the nozzle and cleaning it, or replacing it with an identical model, often resolves the pressure problem for that specific head.
In older systems, particularly those using galvanized pipe or operating with hard water, mineral buildup can coat the inside of the distribution lines. This scaling effectively reduces the pipe’s internal diameter, increasing the friction loss experienced by the water as it travels to the sprinkler heads. Even if the pipe appears clear, a slight reduction in diameter across hundreds of feet of tubing can collectively reduce the available pressure.
Obstructions typically manifest as low pressure in specific zones or individual heads, unlike source issues that affect the entire system uniformly. This distinction helps narrow the diagnosis, pointing the homeowner toward the internal components downstream of the main water source.
Pressure Loss Due to Leaks and Pipe Damage
Pressure loss can also occur when water physically escapes the system due to damage, preventing the necessary volume from reaching the intended sprinkler heads. The most straightforward leaks to identify are visible ones, such as cracked risers, broken spray bodies, or water spraying from a loose fitting above ground. A quick inspection while the system is running can often reveal these obvious breaches.
Detecting underground leaks is more challenging because the damage is hidden, but the signs are often environmental. Indicators of a compromised underground pipe include persistently saturated soil, sections of lawn that are noticeably greener, or the presence of sinkholes. The sound of running water when the irrigation system is supposed to be completely shut off is a definitive sign of a constant leak, often from a broken main line.
The construction material and age of the pipes contribute to the likelihood of damage. Older PVC pipes can become brittle over time and are susceptible to cracking, especially at joints or where they are stressed by ground movement. A break in a main line or a manifold connection, which carries the largest volume of water, results in the most catastrophic pressure drop, often affecting multiple zones simultaneously.
Even small leaks at loose connections or tiny cracks can collectively cause a noticeable pressure decrease, especially in larger systems. A simple diagnostic test involves checking the property’s water meter when all water usage is stopped; if the meter’s indicator is still moving, it confirms water is escaping somewhere, even if the leak is too small to visibly surface.