What machines does ISO 20816-5 cover?

ISO 20816-5 applies to hydraulic machines including vertical Kaplan turbines, vertical Francis turbines, vertical pump-turbines, horizontal Pelton turbines, and vertical pumps operating in hydroelectric power plants. It covers machines with rated speeds typically from 60 to 1000 RPM.

Why are hydro turbine vibration limits different from steam turbines?

Hydraulic machines operate at much lower speeds than steam turbines (often 60–500 RPM vs 1500–3600 RPM). They also experience hydraulic excitation forces from water flow, draft tube surges, and cavitation, which generate different vibration patterns. Vertical machines have additional considerations for thrust bearing vibration.

What is shaft displacement measurement in hydro turbines?

Shaft displacement in hydro turbines is measured using proximity probes mounted near the guide bearings, typically measuring peak-to-peak displacement in micrometers (μm p-p). This is critical for vertical machines where shaft orbit monitoring reveals unbalance, misalignment, and hydraulic instabilities.

Why do horizontal Pelton turbines have different limits?

Horizontal Pelton turbines have lower vibration limits than vertical machines because horizontal bearing arrangements are more sensitive to dynamic forces. The impulse nature of Pelton wheel jet impact also produces different vibration characteristics compared to reaction turbines like Francis and Kaplan.

What should I do if vibration reaches Zone C on a hydro turbine?

Zone C indicates the machine is not suitable for continuous long-term operation. Investigate root causes including runner cavitation, draft tube surge, guide bearing wear, shaft misalignment, or hydraulic resonance. Increase monitoring frequency, plan corrective maintenance during the next scheduled outage, and consider load restrictions.

Free Engineering Tool #023

Vibration Limits — Hydro Turbines & Pump Units

Evaluate vibration severity for hydraulic turbines, pump-turbines, and pumps per ISO 20816-5. Supports bearing housing velocity and shaft displacement measurements.

ISO 20816-5 Zones A/B/C/D Hydro Machines

Results

Vibration Zone

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Measured Value

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Recommendation

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Zone	Boundary	Description

ISO 20816-5 Scope

ISO 20816-5 specifies vibration evaluation criteria for hydraulic machines including Kaplan, Francis, and Pelton turbines, pump-turbines, and pumps used in hydroelectric power plants. It covers both vertical and horizontal machine configurations.

Bearing Housing Vibration — Vertical Machines

Broadband vibration velocity measured on the bearing housing in mm/s RMS, typically 10–1000 Hz range. Applies to vertical Kaplan, Francis, pump-turbine, and pump units.

Zone Boundary	Velocity (mm/s RMS)
A/B	2.8
B/C	5.3
C/D	8.5

Bearing Housing Vibration — Horizontal Pelton

Horizontal Pelton turbines have lower allowable limits due to the bearing arrangement and impulse loading characteristics.

Zone Boundary	Velocity (mm/s RMS)
A/B	2.3
B/C	4.5
C/D	7.1

Shaft Displacement — Vertical Machines

Shaft relative displacement is measured with proximity probes, expressed as peak-to-peak displacement in μm.

Zone Boundary	Displacement (μm p-p)
A/B	80
B/C	160
C/D	260

ℹ️ Note: Vertical hydro machines have unique vibration characteristics due to gravity acting along the shaft axis. Thrust bearing condition and hydraulic forces (draft tube surge, cavitation) significantly affect vibration behavior.

⚠️ Important: Both bearing housing and shaft vibration should be monitored. The worse of the two assessments governs the overall evaluation. Operating conditions (load, head, tailwater level) strongly influence vibration levels in hydro machines.

Vibration Limits for Hydro Turbines per ISO 20816-5 | Vibromera

Published by Nikolai Shelkovenko on February 15, 2026 March 5, 2026