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.
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.
Follow these three steps that will help you determine the hose size you’ll need for your hydraulic systems:
Hose Diameters:
Ensuring you know your hose diameters is essential - let's take a look at what to look out for:
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"
You can find a complete table of dash sizes here. (Note, this is for hose only. Tubes are measured by O.D.)
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. However, it’s a great idea to start with a hydraulic hose guide here, which helps you determine the right hose for your task. For a better understanding of hydraulic threads, refer to our hydraulics fitting guide here.