Rapid opening and closing of the valve is known as Chattering
- Insufficient blow down
- More back pressure due to under size discharge piping
- Insufficient steam flow to the valve
- Lifting with water
The valve is just about to open and has indifinite contact. An audible sound or visible escape of fluid between seat and disc at an inlet static pressure below the popping pressure and at no measurable capacity.
It is the pressure zone between the valve set pressure and the popping pressure . In this pressure zone the valve is only slightly open and therefore discharging a small percentage of its rated capacity.
Simmering can damage a valve because it will leak some fluid that can accumulate in the valve and start corroding it. If a safety valve simmers a lot , consider increasing the valve set point , or if simmering below setpoint , it may need to get repaired.