Pressure Reducing Valves Part One: PRV Offset (Droop)

June 17, 2016 by admin

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. Offset is described by valve manufacturers as a % change in set point pressure as flow changes.  This change is illustrated by the test curves in the graph (Exhibit 1) for two different regulator types. Offset is caused by a number of physical forces that act on the diaphragm, spring and plug as flow changes.  All of the forces acting upon the regulator are illustrated below in Exhibit 2.
Exhibit 1

Exhibit 2

The amount of set point offset (the degree of slope) is dependent upon a number of factors. Some of these factors are intrinsic to all regulator designs, and cannot be controlled by the user.  However, other factors can be controlled by the user, either by regulator selection or installation and operation practices. We will explore those in our next blog posts.

Karl Lutkewitte
Karl Lutkewitte, Steriflow Sales and Product Manager

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