Hydraulic Hose Dimensions: sizing, dash numbers, and selection guide

Hydraulic hose dimensions are a key factor in designing efficient and reliable fluid power systems. Choosing the correct hose size directly impacts fluid velocity, pressure loss, and system performance.

Whether you're working on construction equipment, agricultural machinery, or industrial systems, understanding the principles behind hose inner and outer diameters, dash sizes, and flow capacity is essential. In this guide, we explain what hydraulic hose sizing means, how to interpret dash numbers, and the real-world consequences of incorrect hose selection. Use this article as a complete reference to ensure your hydraulic setup performs at its best, with optimal power transmission and minimal energy loss.

What is hydraulic hose sizing

Proper hydraulic hose sizing is fundamental for ensuring the long-term reliability and peak efficiency of any hydraulic system. It involves selecting the appropriate dimensions for a hose to ensure efficient fluid transport and optimal system performance.

This selection is critical; a hose that is too restrictive can impede fluid flow, causing excessive heat generation, energy loss, and potential component damage due to high velocity and turbulence. Conversely, a hose that is too capacious might lead to sluggish operation and unnecessary material costs. The goal is to match the hose's capacity to the system's flow requirements, ensuring the hydraulic fluid moves at an ideal speed, minimizing pressure drops and maximizing power transmission.

Hydraulic Hose I.D and O.D

Hydraulic hoses are characterized by inner diameter (ID) and outer diameter (OD), both influencing system performance.

Inner Diameter (ID)

A hose's ID dictates how much fluid can pass through it at a given speed, thereby determining fluid flow capacity. An undersized ID causes excessive friction between the fast-moving fluid and the hose walls, leading to significant pressure loss along the hose's length. This means less pressure reaches actuators, reducing system power and efficiency. Conversely, an oversized ID causes fluid to move too slowly, making the system respond poorly. Also, larger hoses are more expensive, heavier, and take up more room, often unnecessarily.

Outer Diameter (OD)

While the inner diameter is crucial for fluid flow, pressure, and velocity, the outer diameter of a hydraulic hose is important for its physical integration into the system, ensuring proper fitting compatibility, secure installation, overall safety, and longevity. The hose's OD dictates the size of fittings, clamps, and other mounting hardware; a mismatch will lead to loose connections, leaks, and potential blow-offs, especially under high pressure.

Dash Size

"Dash size" is a universal numbering system for hydraulic hoses, primarily indicating their inner diameter. Each dash number represents the ID in 1/16-inch increments. For example, a -8 hose has an ID of 8/16 inch (or 1/2 inch). This standardized system ensures quick, consistent identification and compatibility between hoses and fittings, simplifying selection and preventing sizing errors across different manufacturers and applications in hydraulic systems. This system is invaluable for ensuring rapid and error-free component replacement during field repairs.

Hydraulic Hose Size chart

A nomographic chart for hose sizing is a visual tool that quickly determines the correct hose inner diameter (ID). By knowing any two of these three factors—flow rate, flow velocity, or hose ID—a straightedge is used across their respective scales on the chart to find the third, unknown value. This simplifies hose selection, ensuring optimal fluid flow without complex calculations.

Factors to consider when choosing dimensions

Hose selection considers inner diameter for flow and velocity, outer diameter for fit, and length for movement. Temperature, fluid compatibility, and pressure rating are also critical for safe and efficient operation.

Consequences of incorrect sizing

Incorrect hydraulic hose sizing leads to significant problems. Undersized hoses cause excessive pressure drop, increased fluid temperature, fluid degradation, and potential pump cavitation, reducing efficiency and leading to premature hose or component failure, even bursting. For instance, an undersized hose in a bulldozer's hydraulic arm might cause the arm to move slowly and overheat, leading to unexpected downtime during a critical job.

Oversized hoses result in sluggish performance, higher costs, and difficult routing. Both scenarios contribute to leaks, system downtime, safety hazards, environmental contamination, and increased noise and vibration. Proper sizing is crucial for optimal hydraulic system operation and longevity.

Ultimately, meticulous attention to hydraulic hose sizing is paramount for system performance, safety and longevity.