Hydraulic hose sizing nomograph
How to measure a hydraulic hose, how to measure hydraulic hose lengths and sizing hose diameter charts - these are just some of the questions and considerations when it comes to determining the correct size of your hydraulic hose. This hydraulic hose sizing nomograph takes you through all the steps to ensure you size the your hose correctly. This page serves as a practical resource for engineers and technicians working on hydraulic hose sizing.
Hydraulic fluid power works effectively with the right size hose. Get the correct diameter for your hose, and you’ll avoid inefficiencies that result in heat generation and excess back pressure in the motor. Proper hose sizing is especially important within the scope of a project or installation to ensure the hose matches the recommended flow velocity for your specific application.
Follow these three steps that will help you determine the hose size you’ll need for your hydraulic systems:
Introduction to Hydraulic Hoses
Hydraulic hoses are a critical component in any hydraulic system, responsible for transferring fluid under high pressure to power machinery and equipment. Selecting the correct hose is essential for maintaining system efficiency and preventing issues such as pressure loss, excessive heat, or even system damage. One of the most important factors in choosing the right hose is understanding the relationship between flow rate, flow velocity, and hose size.
The inner diameter of the hose plays a crucial role in determining the flow velocity of the fluid. If the diameter is too small, the fluid velocity increases, which can lead to higher pressure drops and potential system damage. On the other hand, a hose with an oversized diameter may result in sluggish system response and reduced efficiency. To ensure optimal performance, it’s important to select a hose size that matches the recommended flow velocity for your specific application.
A nomographic chart is an invaluable tool for this process. By relating flow rate, hose size, and fluid velocity, the chart helps users quickly determine the correct hose size for their needs. Using the chart, you can identify the recommended flow velocity for your application and select the right hose to ensure proper flow capacity and system reliability. This approach not only simplifies the selection process but also helps prevent costly mistakes and ensures your hydraulic system operates at peak performance.
Hose Diameters:
Ensuring you know your hose diameters is essential - let’s take a look at what to look out for:
STAMPED stands for:
Size
Temperature
Application
Material
Pressure
Ends
Delivery
Hose Outer diameter (O.D.):
This is the measurement of the entire span of your hose cross section. It includes the tube, reinforcement, and cover
Inner diameter (I.D.):
The measurement of the empty space inside the hose. Because of wall thickness, your I.D. will always be smaller than the O.D. Your I.D. impacts the flow velocity of the fluid, so getting the measurement correct is critical. An oversized I.D. will give you a slow, listless system performance. Get it too small, and you can expect excessive pressure drops, leaks and even system damage.
Length of hydraulic hose:
This is your maximum reach, from end to end. Keep in mind that the longer the hose, the more the pressure will drop. Hose length contributes to head loss due to friction, so don't make the length any longer than it needs to be.
Getting your dash size
Also called dash number, this is an industry standard that indicates your I.D., with each size going up 1/16". For example:
Dash size 1 = I.D. 1/16" (if using mm, then 1.6 mm)
Dash size 2 = 2/16", or to simplify, 1/8"
Dash size 3 = 3/16"
Recommended Flow Velocities
When selecting a hydraulic hose, following the recommended flow velocities is essential to ensure safe and efficient system operation. For pressure lines, the maximum recommended velocity range typically falls between 7 and 15 feet per second, while suction and return lines require even lower velocities to prevent issues like cavitation and excessive pressure loss. Staying within these recommended velocity ranges helps avoid system damage, overheating, and premature hose failure.
To determine the correct hose size for your application, you’ll need to know two key values: your desired flow rate (in gallons per minute) and your recommended flow velocity (in feet per second). With these two points, you can use a nomographic chart to find the right hose size. Simply lay a straight edge between the two known values on the chart—such as your flow rate and desired velocity—and the intersection with the third vertical line will indicate the correct dash size for your hose.
For example, if your system requires a flow rate of 100 gallons per minute and the recommended flow velocity is 10 feet per second, you would locate these two values on the nomograph. Drawing a straight edge between them, you’ll find the intersection on the third vertical line, which reveals the correct hose size for your application. This process ensures you select a hose that can handle the required flow without exceeding the maximum recommended velocity, reducing the risk of pressure loss, system damage, or inefficient operation.
By always following the recommended flow velocities and using the nomograph to determine the correct hose size, you can optimize your hydraulic system’s performance and extend the life of your hoses and components.
Use the hydraulic hose nomograph chart
A nomograph is essentially a hose sizes chart.
Consider your correct hose I.D., desired flow rate, and recommended flow velocity. If you know any of these two values, you can determine the third using the nomograph chart below
- Pick your two known values.
- Lay a straight edge, intersecting those two values.
- Intersection on the third vertical line reveals the factor you need.
Example: Let’s say your desired flow rate is 16 gallons per minute. Your recommended flow velocity is 20 feet per second. You just need the dash size. You can see where the line drawn against the straight edge passes the dash-size column. In this instance, you need a 5/8" hose, or dash size 12.
Other considerations
Consider rubber-coated hydraulic hoses with braided steel, which gives you an excellent combination of flexibility and durability. For a better understanding of hydraulic threads, refer to our hydraulics fitting guide here.