What typically causes intermittent or spitting discharges from the relief valve during a no flow condition?

Intermittent or spitting discharges from the relief valve during a no flow condition are typically caused by fluctuating inlet pressure. When the pressure fluctuates, it can create conditions that lead to the valve cycling open and closed, resulting in erratic discharges. This behavior is often related to changes in the upstream system, which might be caused by issues such as sudden changes in demand or disturbances in the pressure upstream from the relief valve.

Many factors in the plumbing or backflow prevention system can cause inlet pressure fluctuations, including water hammer or high peaks in water demand in the distribution system. When the inlet pressure varies, it may momentarily exceed the pressure that the relief valve is set to hold back, causing it to release small amounts of liquid intermittently, hence the spitting or intermittent discharge.

A faulty valve installation, blockage in the system, or improper testing procedures could lead to different types of issues but are not typically associated with the specific behavior described in the question, which directly relates to variations in inlet pressure. Understanding this relationship helps in diagnosing and troubleshooting issues effectively in backflow prevention systems.