How to measure hydraulic hose

Identifying the size of hydraulic hose is crucial so hydraulic system’s do not have to be altered, in our latest blog we explain how to measure this and hopefully make your life easier!

Many hose installers are not trained on how to correctly measure and specify hose length. As a result, a replacement hose may end up being either a little shorter or a little longer than the original part.

When requesting a hose assembly, its length can generally be identified in two ways: overall length, or cut length. Overall length is the most common way to identify hose length and it is typically used when ordering hydraulic hoses.

To measure the size we can use two nomenclatures: Nominal diameter and Inches.

Hydraulic Hose Size

The Nominal Diameter: also known by its abbreviation DN, is the measurement in millimetres of the interior of the hose.

Inches:  this measurement of length comes from the English nomenclature. 1 inch equals 25.40 millimetres, also taking the inside of the hose as a reference.

Read the hydraulic hose markings

Modern hoses are clearly marked with the hose type, size, pressure rating and cure date. Do not rely on this information if you think the system pressure may be greater but also never fit a new hose that is rated with a lower size or pressure.

Each hose on a system may have a different rating so make sure you check each one. Some will be high flow and high pressure while other parts of the circuit may require lower flow and lower working pressures. Remember that cylinder intensification can result in pressure higher than the pump setting.

Include the manufacturer markings in the comments box if no standard or codes are provided.

Identify the hose size

Measure and specify the ID, not the OD. For example 3/4” is the hose bore size, not the outside diameter. Because of different wall thicknesses, you cannot rely on measuring the outside diameter of a hose.

Identifying the type of hydraulic hose or rating

Hydraulic hoses are rated for different pressures, temperatures, fluids and/or environments. This often depends on the number of internal wire braids, the rubber used and ferrule or end fittings etc. For example, R2T hose has 2 wire braids and is commonly used for low to medium pressure hydraulic fluid. 4SP hose has 4 wire braids in within the rubber and is capable of higher pressures.

Without cutting the hose you will not be able to see how many wire braids are used within the hose.

Hose fitting materials and corrosion protection

Hose fittings are generally plated steel but often for marine applications will be Stainless Steel. Always use a lubricating paste to on stainless threads to stop them binding when you assemble them. If hoses are on a boat’s deck, or similar marine environment then we recommend Denso tape is used to protect them.

Consequences of an error in the hose size:

– If you put a hose smaller than the one we must place, you will cause strangulation in the oil passage and will increase the pressure drop and increase the heating and speed of the oil.
– If you put a hose with a larger internal diameter than the necessary one, you will cause the oil to pass slower, generating turbulence in the circuit that will affect it, causing noise and vibrations.

For more information on pipe sizing visit our Pipe Sizing Nomogram available to freely download on our Technical Download Library HERE.