How to determine the Equipment Reliability Operating Envelope of a centrifugal pump

If the centrifugal pump flow is too high or too low hydraulic disturbances will be present that can change the pumped fluid pressure and/or temperature. Since the majority of mechanical seal applications use the pumped fluid in the seal chamber, the seal chamber pressure and/or temperature will be affected. These changes will directly impact mechanical seal life and reliability.

This article is among the best practices presented by Michael E Forsthoffer and Michael Sean Forsthoffer at the 2016 Asia Turbomachinery & Pump Symposium.

Decreased Pump Flow:

 Increased P2

 Decreased P1

 Decreased S.G.

Increased Pump Flow:

 Decreased P2

 Increased P1

 Increased S.G.

Figure shows a typical centrifugal pump head vs. flow curve with the following items noted:

 The “Desirable Region” of Operation – Heart of the Curve or EROE

 Regions of Hydraulic Disturbances – On the upper portion of the curve

 The Pump Components affected – On the lower portion of the curve

The “Heart of the Curve” is the flow region for any centrifugal pump that will be free of Hydraulic Disturbances and where the seal fluid should be free of vapor if the seal fluid conditions stated on the Pump and Seal Data Sheets are present during pump field operation. This Flow Region is also called the: EROE – The Equipment Reliability Operating Envelope.

Figure presents facts concerning the EROE.

1. The eroe flow range is + 10% and – 50% of the pump best efficiency point (bep) flow

2. All “bad actor pumps” – (more than one component failure per year) should be checked for eroe

3. To determine that the pump is operating in eroe:

 Calculate the pump head required

 Measure the flow

 Plot the intersection of head & flow on the pump shop test curve