What does the adjusting screw on a spring-loaded relief valve do?
It changes the spring tension, which directly sets the valve’s opening pressure (set pressure).
What is the bonnet of a spring-loaded relief valve?
It’s the housing that encloses the spring. An open bonnet exposes the spring to the atmosphere, while a closed bonnet seals it from the environment.
What is the purpose of the test lever on a PRV?
It manually lifts the disc by pulling the stem, allowing field testing of valve operation without reaching full set pressure.
What is the function of the spring in a relief valve?
The spring provides the force that keeps the disc seated against the nozzle until the set pressure is reached.
What is the stem (or spindle) in a PRV?
It connects the spring to the disc and transmits the spring force that keeps the valve closed.
What does the upper adjusting ring (or blowdown ring) do?
It controls the valve’s opening characteristics and blowdown by directing flow under the disc
What is blowdown in a pressure relief valve?
The difference between the opening pressure and reseating pressure, typically 2–20% of the set pressure.
Why isn’t blowdown usually zero?
Because real valves don’t open and close at the exact same pressure—some pressure drop is needed to reseat the disc and stop flow.
What is the function of the disc in a PRV?
It seals against the nozzle to prevent flow until system pressure exceeds the set pressure, then lifts to allow pressure relief.
What feature on the disc helps create the “pop” action?
A small lip or skirt on the disc that directs flow into the huddling chamber, accelerating disc lift.
What is the lower adjusting ring (nozzle ring)?
A ring on the inlet nozzle below the disc that affects how the valve closes and reseats by controlling pressure under the disc during closure.
How does lowering the lower adjusting ring affect valve behavior?
It shortens blowdown (valve closes sooner) but increases simmer and causes a slower opening.
How does raising the lower adjusting ring affect valve behavior?
It lengthens blowdown (valve closes later) but provides quicker pop action and less simmer.
What is “simmer” in a PRV?
The slight flow or leakage through the disc just before the valve reaches full set pressure.
What is the nozzle in a spring-loaded PRV?
It’s the inlet passage that directs pressurized fluid into the valve and provides a sealing surface for the disc.
What is the huddling chamber?
The space between the disc and the lower adjusting ring (and upper ring if present) that builds pressure to help lift the disc rapidly during opening.
What happens when you reduce the volume of the huddling chamber?
The valve tends to close sooner (shorter blowdown) but may open more slowly and experience more simmer.
What happens when you increase the volume of the huddling chamber?
The valve opens more rapidly (stronger pop action) but has a longer blowdown before reseating.
What do the upper and lower adjusting rings together control?
They fine-tune the valve’s opening and closing characteristics, determining how quickly it pops open and how smoothly it reseats.
What is the main purpose of all these adjustments (rings, spring, screw)?
To ensure the valve opens at the correct pressure, relieves safely and rapidly, and reseats properly without excessive leakage or delay.
