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 inches matter, the confusion about properly measuring hose length can result in delays and extra expense.
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 Parker hydraulic hoses.
Overall hose assembly length
When assembling a hose, it is important to note when the "overall length" (OAL) is critical. In most industrial applications (such as water or general purpose) the OAL is not critical, but in many hydraulic applications the OAL can be critical due to space restrictions. The OAL of a hose assembly can be determined by measuring a hose assembly from end-to-end.
Here are some examples of a standard hose assembly length for a straight fitting, 90º fitting, and 45º fitting. It is important to remember the following when calculating the OAL:
- Male threaded ends are measured from the end of their threads.
- Female threaded ends and flanged ends are measured from their sealing surface.
- Angled ends are measured from the center of their sealing surface.
Hose cut length
The hose cut length is measured based on specs. The hose cut length for a hose assembly is calculated by subtracting the cut-off factor (distance from the bottom of the ferrule or collar to the end of the fitting or an internal sealing surface). In the example below, take special note of Dimension "B." Knowing the overall length of the assembly desired, subtract the "B" dimension for each fitting from the overall length to obtain the hose cut length.
Important factors for identifying hose length
Whether you are identifying hose lengths by OAL or hose cut length, remember that length will change under pressure through expansion or contraction (typically between 2% to 4%). Other important factors to consider include:
- Make note of machine vibration and motion, as well as the routing design.
- Allow enough length so that the fittings are not subjected to pull-off forces when parts reach their limits of travel.
- Avoid stretching the hoses, as this can restrict fluid flow.
- Avoid clamping hoses at their bends, to allow for length changes during pressurization.
- Do not clamp high and low pressure lines together.
- Cut the new hose the same length as the one being removed when replacing hoses.
If the replacement hose is too short, pressure may cause the host to contract and be stretched, reducing service life.
Parker Hannifin has some great resources for hydraulic hose, fittings and equipment including online literature that outlines the proper hose assembly techniques. The Parker HoseFinder mobile app is also a useful tool for on-the-go assistance for choosing the right hose and fittings for any application.
Article contributed by Kyri McDonough, marketing services manager at Hose Products Division, Parker Hannifin.
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