How to Use the Nomographic Chart to Size Your Hydraulic Hoses

Hydraulic Hoses are essential for efficient fluid power systems, and choosing the right size can make all the difference. If you’re unsure how to match flow rate, velocity, and hose ID, a nomographic chart can simplify the process. In this guide, we’ll walk you through using nomographs to size hoses accurately, avoid pressure drops, and extend system life. Whether you’re designing new systems or upgrading existing lines, these tips help ensure your hoses perform reliably under all operating conditions.

Understanding Hydraulic Hose Sizing

What is Hydraulic Hose Sizing?

Hydraulic hose sizing is all about matching the right hose to your system’s flow requirements. It ensures fluid moves efficiently through pumps, valves, and actuators. Using the correct hose prevents problems like pressure drops, excessive heating, and reduced system efficiency. A hose that’s too small can overheat fluid and stress components. Too large, and fluid moves sluggishly, wasting energy and slowing system response. They can also fail prematurely if sizing isn’t considered properly.

Inner Diameter (ID) vs Outer Diameter (OD)

The inner diameter, or ID, controls how fast the fluid travels inside the hose. Smaller IDs increase velocity but can cause pressure loss or turbulence. Larger IDs slow flow, reducing performance. The outer diameter, or OD, affects how the hose fits into your system. It determines compatibility with fittings, clamps, and mounting spaces. OD includes the hose wall, reinforcement, and cover, so it’s always larger than ID.

Both ID and OD matter. One controls fluid flow, the other ensures the hose can connect and move safely in the system.

What is Dash Size?

Dash size is a standardized way to describe hose IDs. Each dash represents 1/16 inch of inner diameter. They make it easy to match hoses to fittings across different brands.

They are simple to convert: Dash × 1/16 = ID in inches. Use it to quickly pick hoses without complex calculations. They also help ensure replacements or upgrades fit perfectly.

Introduction to Nomographic Charts for Hydraulic Hose Sizing

What is a Nomographic Chart?

A nomographic chart, or nomograph, is a visual tool for sizing hydraulic hoses. It connects three key factors: flow rate, hose inner diameter, and fluid velocity. Instead of doing complex formulas, we can use a straightedge to find the correct hose size. It’s simple, fast, and reduces guesswork. Engineers and technicians use it to quickly match hoses to system requirements, whether for pressure lines, suction lines, or return lines.

Benefits of Using a Nomographic Chart

Using a nomograph saves time and cuts calculation errors.

• Speeds up hose selection during design or repairs.

• Prevents system damage caused by undersized or oversized hoses.

• Helps pick the right hose for both high-pressure and suction lines.

• Reduces trial-and-error and downtime in industrial setups.

It makes sizing more predictable, especially when working with multiple hoses or varying flow rates.

Key Variables in Hose Nomographs

Nomographs rely on three main variables:

Knowing any two allows us to find the third. For example, if we know the desired flow rate and velocity, the nomograph shows the proper hose ID. This approach simplifies sizing across various systems and fluids.

Step-by-Step Guide to Using the Nomographic Chart

Step 1 – Identify Your System Requirements

First, determine your system’s required flow rate. Know if the hose will serve as a suction, pressure, or return line. Check operating temperatures and fluid viscosity, since hotter or thicker fluids affect velocity and pressure. These factors are crucial for picking the correct hose size.

Step 2 – Understand Your Hose Specifications

Next, review your hose specifications. Look at inner diameter (ID), outer diameter (OD), wall thickness, and hose length. Measure the maximum reach to prevent excessive pressure drops. Remember, longer hoses or small IDs can reduce system efficiency.

Step 3 – Pick Two Known Values

Using the nomograph requires knowing any two variables: flow rate, velocity, or hose ID. Once you have these, the third variable can be determined easily. This is the core principle behind hydraulic hose sizing nomographs.

Step 4 – Lay a Straightedge Across the Chart

Align your two known values on the chart using a straightedge. Draw a line connecting them to find the intersection on the third scale. For pressure lines, stay within the maximum recommended velocity. Suction lines usually require slower speeds to prevent cavitation.

Tips:

• Use lower velocity for continuous flow or high-viscosity fluids.

• Keep your straightedge steady to avoid reading errors.

• Read the dash size from the intersection point in the center column.

Step 5 – Verify Hose Selection

Finally, cross-check the selected dash size against system constraints. Consider fittings, routing, temperature limits, and pressure ratings. For continuous operation or viscous fluids, a slightly larger hose ID can improve performance and extend hose life.

Practical Examples of Using a Nomographic Chart

Example 1 – Pressure Line Hose Sizing

Suppose your hydraulic system requires a flow rate of 20 GPM and the maximum recommended velocity is 15 ft/s. Using the nomograph, you align these values and find the intersection on the dash size column. The chart may recommend a -12 hose (5/8" ID).

Risks of incorrect sizing:

• Too small ID: Fluid moves too fast, causing erosion, heat buildup, and potential hose failure.

• Too large ID: Flow slows, system response lags, and pressure may drop.

Example 2 – Suction Line Hose Sizing

Now consider a suction line with a flow rate of 40 L/min and a fluid velocity of 4.5 m/s. Using the nomograph, you connect flow rate and velocity to determine the correct dash size. The chart may indicate a -10 hose (~1/2" ID).

Key considerations:

• Suction hoses are sensitive to velocity.

• Excessive speed can cause cavitation, damaging pumps and reducing efficiency.

• Proper sizing prevents vacuum pockets and ensures smooth fluid intake.

Example 3 – Continuous vs Intermittent Flow

Velocity choice depends on how the system operates.

• Continuous flow or long hoses: Use the lower end of the recommended velocity range to reduce heat, pressure loss, and wear.

• Intermittent or short hoses: Higher velocities are acceptable without stressing the hose.

Factors to Consider When Selecting Hose Size

Selecting the right hydraulic hose goes beyond dash numbers. Several factors influence performance, safety, and longevity.

Fluid Type and Compatibility

The fluid traveling through the hose affects material choice. Oils, chemicals, and water-based fluids interact differently with hose liners. Using incompatible hoses can lead to swelling, leaks, or rapid degradation. Always check manufacturer compatibility charts.

Operating Temperature and Pressure

Hoses must handle system temperatures and pressures. High heat increases fluid viscosity and accelerates wear. Exceeding pressure ratings can cause blowouts. Select hoses rated slightly above your maximum system requirements for safety.

Hose Length and Routing Constraints

Long hoses create more friction and pressure drop. Tight bends, twists, or obstructions reduce flow efficiency. Plan the hose path carefully and measure maximum reach to prevent unnecessary losses.

Suction vs Discharge Applications

Suction hoses require lower velocities to avoid cavitation, whereas discharge hoses can handle higher speeds. Knowing the application type ensures proper flow rates and prevents pump or hose damage.

Maintenance and Replacement Frequency

Frequent system use, continuous flow, or high-viscosity fluids may require larger hoses or higher-grade materials. Consider how often hoses will be inspected or replaced to minimize downtime and maintain performance.

Conclusion

Mastering the use of nomographic charts takes the guesswork out of selecting Hydraulic Hoses. By aligning flow rate, fluid velocity, and dash size, you can make faster, safer decisions for pressure, suction, and return lines.

For companies and technicians looking for reliable hose solutions, Qingdao Honest Rubber Co., Ltd. offers a wide range of high-quality hydraulic hoses. Using the right hose size with trusted products ensures longer life, smoother operation, and fewer maintenance issues—helping your system run at peak efficiency.

FAQ

Why is proper hose sizing important?

Proper hose sizing ensures efficient fluid flow, reduces pressure drops, prevents overheating, and prolongs hose and system component life.

How do I choose the right dash size?

The dash size represents the hose’s inner diameter in 1/16-inch increments. Use a nomograph or conversion chart to match the dash size with your system’s flow rate and velocity.

What factors affect hydraulic hose selection?

Key factors include fluid type, operating temperature, system pressure, hose length, routing constraints, suction versus discharge applications, and maintenance frequency.

Can I use the same hose for suction and pressure lines?

No. Suction hoses require lower fluid velocities to prevent cavitation, while pressure hoses can handle higher speeds. Proper sizing ensures safe and efficient operation.

Should I select a larger hose for continuous flow?

Yes. For continuous or high-viscosity fluid applications, choosing a slightly larger hose ID reduces pressure loss, heat, and wear, improving system reliability.