What is PRV Offset (Droop) and Why Does it Occur?
All pressure reducing valves exhibit a drop in set point pressure (Offset, Droop) as flow through the valve increases.
What is Offset (Droop) in a Pressure Regulator?
Pressure regulator droop/offset is described by valve manufacturers as a % change in set point pressure as flow changes.
This change is illustrated by the test droop curves in the graph for two different regulator types.
Why Does PRV Offset Occur?
Offset is caused a number of physical forces that act on the diaphragm, spring and plug as flow changes.
Factors Affecting the Amount of Offset
The amount of set point offset (the degree of slope) / droop slope is dependent upon a number of factors.
1. Intrinsic (Uncontrollable) Factors
These are inherent to all regulator designs and cannot be controlled by the user.
2. Controllable (User-Dependent) Factors
These can be influenced through regulator selection, installation, and operational practices.