ISO 14694: Industrial fans — Specifications for balance quality and vibration levels

Summary

ISO 14694 provides a dedicated set of requirements for the balancing and acceptable vibration levels of industrial fans. It recognizes that fans are a unique class of machinery and tailors the more general principles found in standards like ISO 1940-1 (balancing) and ISO 10816 (vibration) to their specific characteristics. The standard is essential for fan manufacturers, system designers, and end-users to ensure that fans operate smoothly, safely, and meet performance expectations. It provides a clear, unified framework for both the initial balance quality of the impeller and the final, in-situ vibration of the complete fan assembly.

Table of Contents (Conceptual Structure)

The standard is logically divided into two main technical sections: one covering balance quality and the other covering operational vibration.

1. 1. Scope and Definitions:

   This initial chapter establishes the standard’s specific focus, clarifying that its requirements apply to industrial fans of all types (centrifugal, axial, mixed-flow) and sizes, intended for terrestrial applications. It explicitly excludes fans designed for highly specialized uses such as aircraft propulsion or air-cushion vehicles. The section also provides a comprehensive set of definitions for terminology used throughout the document, ensuring that terms like “rigid support,” “flexible support,” and specific fan components have a single, unambiguous meaning. This foundational chapter is crucial for ensuring that both the fan manufacturer and the end-user have a common language and understanding when specifying, testing, and accepting industrial fans based on their vibration and balance characteristics.

2. 2. Balance Quality Requirements for the Impeller:

   This chapter provides the critical specifications for the balance quality of the fan impeller (rotor) as a standalone component, before it is assembled into the fan housing. It tailors the general-purpose G-grades from ISO 1940-1 to the specific needs of fans by establishing a series of “Balance Quality Grades for Fans” (BV categories). The standard provides a detailed table that maps different fan types and applications to these BV categories (e.g., BV-5, BV-4, BV-3), which in turn correspond to specific G-Grades. For instance, a fan for general-purpose ventilation might only require a G6.3, while a high-speed, critical-service fan might require a much stricter G2.5. This allows a purchaser to specify a precise and appropriate level of balance quality for the impeller based on its intended operational speed and application, ensuring that the primary source of vibration—unbalance—is controlled at the source.

3. 3. Vibration Limits for the Assembled Fan:

   This chapter addresses the vibration of the complete fan unit—impeller, shaft, bearings, and housing—as a fully assembled system operating under specified test conditions. It establishes a set of “Fan Vibration Categories” (FV) that define acceptable vibration levels for different applications and installation types. The standard provides a clear table listing the maximum allowable broadband RMS velocity for each category, measured on the fan’s bearing housings. These categories are crucial for acceptance testing and take into account factors such as the fan’s power consumption, the type of support structure (rigid or flexible), and the criticality of the application. For example, a fan designated for a non-critical application on a flexible base might be assigned a more lenient category like FV-5, whereas a high-power, critical fan on a rigid foundation would be held to a much stricter category like FV-1, requiring significantly lower vibration levels for acceptance.

4. 4. Test Procedures and Acceptance Criteria:

   This final chapter provides the practical, actionable framework for verifying compliance with the standard. It clearly separates the verification process into two distinct stages. First, it mandates that the balance quality of the fan impeller must be confirmed *before* assembly, by performing a balance check on a calibrated balancing machine to ensure the residual unbalance is within the tolerance specified by its BV category. Second, it defines the procedure for the operational vibration test of the fully assembled fan. It specifies that the fan must be run at its operational speed under defined load conditions, and that vibration measurements must be taken on the bearing housings in accordance with the general procedures of ISO 10816-1. The acceptance criterion is straightforward: the highest measured broadband RMS velocity must not exceed the limit for the contractually specified FV category. This section provides a clear, pass/fail basis for both manufacturers and end-users to confirm that the fan meets its specified performance requirements.

Key Concepts

• Application-Specific Guidance: The main value of this standard is that it takes general-purpose standards and refines them for one specific, very common machine type. The BV (Balance Vibration) and FV (Fan Vibration) categories provide much clearer and more direct guidance than trying to interpret the broader machine groups in ISO 10816-3.
• Balancing vs. Operational Vibration: The standard clearly separates the two concepts. First, the fan *impeller* must be balanced to a specific quality grade (BV category) on a balancing machine. Second, the *entire fan assembly* must meet a specific operational vibration limit (FV category) when installed and running. Good balance is necessary but not sufficient for low operational vibration, which is also affected by alignment, foundation, and aerodynamic forces.
• Rigid vs. Flexible Support: Like the general vibration standards, ISO 14694 recognizes the critical role of the fan’s support structure and provides different vibration limits for rigid and flexible foundations.

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