ISO 8426-1:2025 PDF

Name: ISO 8426-1:2025 — Hydraulic fluid power — Determination of derived displacement of positive displacement pumps and motors — Part 1: Two-step Toet method
SKU: ISO 8426-1:2025
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Hydraulic fluid power — Determination of derived displacement of positive displacement pumps and motors — Part 1: Two-step Toet method

Название (английский):

ISO 8426-1:2025

Hydraulic fluid power — Determination of derived displacement of positive displacement pumps and motors — Part 1: Two-step Toet method

Статус документа:: Действующий
Формат:: Электронный (PDF)
Количество страниц:: 16
Дата публикации:: 14 августа 2025 г.
Издание:: ISO IS 8426 edition 1 version 1
ICS:: 23.100.10

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Описание (английский):

This document specifies the two-step Toet method for the determination of the derived displacement of hydraulic fluid power positive displacement pumps and motors under steady-state conditions. A value for the derived displacement is determined from measurements at multiple shaft speeds.

Abstract

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Упомянутые в описании и другие стандарты ISO

Overview

ISO 8426-1:2025 - "Hydraulic fluid power - Determination of derived displacement of positive displacement pumps and motors - Part 1: Two-step Toet method" specifies a standardized laboratory method to determine the derived displacement (derived capacity) of positive-displacement hydraulic pumps and motors under steady-state conditions. The standard defines how to collect flow and speed data across multiple shaft speeds and differential pressures and prescribes the two-step Toet regression procedure to compute the derived displacement value.

Key technical topics and requirements

Scope and definitions: Applies to hydraulic fluid power positive-displacement pumps and motors. Terminology follows ISO 5598.

Test planning:

Use five or more shaft speeds and five or more differential pressures (≥25 measurement points total).
Shaft speeds and differential pressures should be increased in approximately equal increments; targeted values must meet a ±5% tolerance to avoid clustering.
Guidance for maximum targeted differential pressure is provided relative to rated pressure (different rules for ≤50 bar and >50 bar).

Measurement requirements:

Follow ISO 4409:2019 for basic steady-state testing, flowmeter placement, fluid properties, temperature, and measurement accuracy classes.
Special considerations for variable displacement units, reverse-flow operation, and whether the unit is tested as a pump or motor (results can differ).

Computation - Two-step Toet method:

Step 1: For each targeted differential pressure, perform ordinary least squares (OLS) regression of high-pressure flow rate versus shaft speed to obtain slopes (α_i).
Step 2: Regress the obtained slopes α_i versus differential pressure Δp; the intercept at Δp = 0 is the derived displacement V (slope of flow vs speed at zero Δp).
Formulae and fitting guidance are provided in Annex B; test report examples are in Annex A.

Reporting:

Required test report information includes unit ID, test date/location, speed and pressure ranges, fluid properties, raw measured values (p_in, p_out, Δp, n, flow, temperature), derived displacement, coefficients and correlation statistics.

Practical applications and users

ISO 8426-1:2025 is intended for:

Test laboratories and certification bodies performing hydraulic component characterization.

Manufacturers of hydraulic pumps and motors for product development, quality control and datasheet validation.

R&D and engineering teams assessing volumetric performance and design changes.

Specifiers and procurement engineers who need comparable, traceable derived displacement data for system design and component selection.

Using this standard ensures repeatable, comparable derived-displacement measurements that support performance verification, troubleshooting, and compliance with industry best practices.

ISO 8426-1:2025 PDF

Abstract

Похожие стандарты

Overview

Key technical topics and requirements

Practical applications and users

Related standards

Технические детали

ISO 4409:2019

Hydraulic fluid power — Positive-displacement pumps, motors and integral transmissions — Methods of testing a…

ISO 5598:1985

Fluid power systems and components — Vocabulary

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