ISO/TR 21784:2018

Plain bearings - Spray nozzle type directed lubrication for tilting pad bearings

Directed lubrication is an advanced technology that is capable of reducing the power loss and improving the performance of tilting pad type bearings. Unlike flooded lubrication, where the bearing components remain permanently submerged in an oil filled housing, with directed lubrication the components are not submerged and the oil is delivered from an external source directly to the working surfaces of the tilting pads after which it falls freely away to be drained from the bottom of the housing. There are several alternative methods of realising the benefits of directed lubrication in tilting pad bearing designs. As an example, this document specifies a spray nozzle type directed lubrication system where lubricant is supplied to each pad through nozzles mounted between the pads in tilting pad thrust and journal bearings. The design concept of this type of lubrication is described.

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General Information

• Status: Published
• Publication Date: 12-Sep-2018
• ICS: 21.100.10 - Plain bearings
• Technical Committee: ISO/TC 123/SC 7 - Special types of plain bearings
• Drafting Committee: ISO/TC 123/SC 7 - Special types of plain bearings
• Current Stage: 6060 - International Standard published
• Start Date: 13-Sep-2018
• Completion Date: 13-Dec-2025

Overview

ISO/TR 21784:2018 - Plain bearings - Spray nozzle type directed lubrication for tilting pad bearings - describes the design concept and practical implementation of spray nozzle directed lubrication for tilting pad thrust and journal bearings. The technical report explains how directed lubrication differs from traditional flooded lubrication: oil is injected directly to pad working surfaces via nozzles between pads, the bearing housing is not filled, and excess oil is drained. The goal is to reduce power loss, minimize churning losses and improve overall performance and energy efficiency in rotating machinery (turbines, generators, compressors, pumps).

Key topics and requirements

• Lubrication concept: Spray nozzle type directed lubrication supplies lubricant to each pad through nozzles mounted between pads; nozzles can also act as pad stops and aid assembly/disassembly.
• Power-loss reduction: Directed lubrication reduces churning losses inherent to flooded systems, especially at high speeds, resulting in significant energy savings.
• Oil flow and cooling: The report recommends limiting oil temperature rise through the bearing to about 15–20 °C. Required oil flow rate is calculated from estimated power loss using the relationship between power, oil heat capacity, density and allowable temperature rise.
• Nozzle sizing and arrangement: ISO/TR 21784 provides formulae and guidance linking nozzle hole diameter, number of holes, nozzle count per bearing and a flow coefficient (K) to achieve the required oil flow and spray distribution. Specific nozzle types (A, B, C, D) and selection guidance (e.g., Type C for pad axial width < ~130 mm) are described.
• Oil supply pressure and velocities: Typical oil supply pressures are 0.10–0.15 MPa. Design of inlet passages should limit oil velocity to ≤ 3 m/s to avoid pressure losses; discharge geometry should allow free drainage, keeping discharge velocity low (example: < 0.15 m/s by sizing discharge hole diameter relative to collar width).
• Seal and drainage options: For journal bearings, seal rings are normally removed to permit axial drainage; where used, seal clearances are increased to allow oil discharge.

Applications and users

Who benefits from ISO/TR 21784:

• Bearing designers and OEMs developing tilting pad thrust and journal bearings with directed lubrication
• Rotating machinery engineers and plant reliability teams seeking energy-efficient bearing solutions
• Maintenance engineers specifying retrofit or new bearing lubrication systems for turbines, compressors, pumps and generators
• Consultants and specification writers preparing procurement or performance criteria for bearings and lubrication systems

Practical benefits include reduced bearing power loss, smaller cooling systems, simplified housing designs and improved plant efficiency.

Related standards

• Prepared by ISO/TC 123 (Plain bearings). For complete implementation consider other ISO standards and technical reports on plain bearing design, lubrication and bearing testing published by ISO/TC 123.

Standards Content (Sample)

TECHNICAL ISO/TR
REPORT 21784
First edition
2018-09
Plain bearings — Spray nozzle type
directed lubrication for tilting pad
bearings
Titre manque
Reference number
©
ISO 2018
© ISO 2018
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
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ii © ISO 2018 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms . 1
5 Reduction effect of power loss by spray nozzle type directed lubrication systems.2
6 Lubrication system . 4
6.1 Tilting pad thrust bearing . 4
6.2 Tilting pad journal bearing . 5
7 Oil supply system of spray nozzle type directed lubrication . 6
7.1 General . 6
7.2 Tilting pad thrust bearing . 6
7.3 Tilting pad journal bearing . 7
7.4 Oil flow . 7
7.5 Oil supply pressure . 8
8 Structure of oil inlet and outlet (drainage) on nozzle type directed lubrication .8
8.1 Tilting pad thrust bearing . 8
8.2 Tilting pad journal bearing .10
Bibliography .12
Foreword
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This document was prepared by Technical Committee ISO/TC 123, Plain bearings, Subcommittee SC 7,
Special types of plain bearings.
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iv © ISO 2018 – All rights reserved

Introduction
These days, rotating machines such as turbines, generators, compressors, pumps, etc. tend to be
increasing in speed and reducing in size. Bearings used in such machines can cause large power losses,
which not only degrades machine performance but also results in the associated cooling system being
larger in size. Directed lubrication type bearings can reduce the power loss significantly. They are
energy-saving bearings that can simplify facilities and improve plant efficiency.
TECHNICAL REPORT ISO/TR 21784:2018(E)
Plain bearings — Spray nozzle type directed lubrication for
tilting pad bearings
1 Scope
Directed lubrication is an advanced technology that is capable of reducing the power loss and improving
the performance of tilting pad type bearings. Unlike flooded lubrication, where the bearing components
remain permanently submerged in an oil filled housing, with directed lubrication the components are
not submerged and the oil is delivered from an external source directly to the working surfaces of
the tilting pads after which it falls freely away to be drained from the bottom of the housing. There
are several alternative methods of realising the benefits of directed lubrication in tilting pad bearing
designs. As an example, this document specifies a spray nozzle type directed lubrication system where
lubricant is supplied to each pad through nozzles mounted between the pads in tilting pad thrust and
journal bearings. The design concept of this type of lubrication is described.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https: //www .iso .org/obp
— IEC Electropedia: available at http: //www .electropedia .org/
4 Symbols and abbreviated terms
For the purposes of this document, the following symbols apply.
Table 1 — Symbols and units
Symbol Explanation Unit
B Thrust collar width m
tc
c Specific heat capacity of lubricant J/(kg·K)
p
D Diameter of discharge oil hole m
d
d Hole diameter of nozzle m
h
K Coefficient of oil flow rate 1
Q
n Number of holes per nozzle 1
h
n Number of nozzles per bearing 1
n
P Power loss W
p Oil supply pressure Pa
en
Q Total oil flow rate m /s
Q Oil flow rate per nozzle m /s
n
ΔT Oil temperature rise K
ρ Density of lubricant kg/m
5 Reduction effect of power loss by spray nozzle type directed lubrication systems
The effect of power loss reduction by the spray nozzle type directed lubrication system is shown with
regard to tilting pad thrust bearings. The power loss of tilting pad thrust bearings arranged for floo
...