How to Choose a Hydraulic Hose — 7 Steps to the Right Hose
A wrongly chosen hose either bursts early or stops the machine. We work through the seven questions that need answering when selecting a hose — from size and pressure to temperature and end type.
6 min read · 10-row dimension table · 5 frequently asked questions
Seven questions, one correct hose
Hydraulic hose selection is carried out under seven headings, known in the trade by the abbreviation STAMPED. Answer them in order and the chance of ending up with the wrong product is almost nil.
1. Size
Hose size is quoted by inner diameter. Choose the bore too small and flow velocity rises, the oil heats up and pressure is lost; choose it too large and you pay for capacity and space you do not need. The accepted rule is to keep flow velocity between 4 and 6 m/s in pressure lines and between 0.6 and 1.2 m/s in suction lines.
If you do not know the size of the hose you have, measure the bore at the cut end or read the marking stamped on the ferrule.
2. Temperature
Two temperatures matter: that of the fluid and that of the surroundings the hose runs through. Hoses with a standard NBR liner work between –40 °C and +100 °C. A hose routed close to an exhaust manifold can see far higher ambient temperatures, in which case a heat sleeve or fire-resistant cover is needed.
Running continuously at the upper limit shortens hose life sharply: every 10 °C increase roughly halves it.
3. Application
Where the hose runs, how much it moves and whether it rubs are all decisive. On a hose working on a moving boom, bend radius becomes critical. Where abrasion is present, a spiral guard or plastic sleeve should be fitted.
4. Media
An NBR liner is sufficient for standard hydraulic oil. However, water-based fluids, brake fluid, phosphate esters and non-oil chemicals call for a different liner. The wrong material causes the liner to swell and the hose to break up from the inside.
5. Pressure
The working pressure of the hose must exceed the peak pressure of the system — not its average. Pressure spikes generated when valves close can reach twice system pressure. The standard safety factor is 4:1: burst pressure is at least four times working pressure.
6. Ends
The fitting type, size and angle (straight, 45°, 90°) are specified separately for each end. End type is dictated by the machine's connection; this is a question of compatibility, not preference.
7. Delivery and length
Hose length is established by measuring between the two connection points with the hose in its installed position. What is quoted is the overall length from fitting end to fitting end, not the cut length of the hose.
Common mistakes when measuring length
- Measuring too short: hose contracts under pressure. Allow 2–4% on the length.
- Starting the bend at the ferrule: the hose must not bend immediately at the ferrule outlet; leave at least one hose diameter of straight run.
- Forcing the bend radius: bending tighter than the catalogue figure breaks the reinforcement wires and the hose bursts at exactly that point.
- Fitting the hose twisted: twisting the hose about its axis during assembly cuts its life dramatically. The printed lay line on the hose should stay straight.
When to replace a hose
If any of the following is present, replace the hose rather than waiting for it to burst:
- cracks, blisters or exposed wire in the outer cover,
- weeping or damp marks around the ferrule,
- permanent deformation — the hose crushed or flattened,
- corrosion or signs of slippage on the ferrule.
On lines in continuous service a scheduled replacement interval is applied as well; two years is a common figure for hoses working under heavy conditions.
Hose bore, DN equivalent and recommended flow rate
| Inch | DN | Bore | Pressure line (4–6 m/s) | Suction line (0.6–1.2 m/s) |
|---|---|---|---|---|
| 1/4" | DN6 | 6.4 mm | 8 – 12 l/min | 1 – 2 l/min |
| 5/16" | DN8 | 7.9 mm | 12 – 18 l/min | 2 – 3 l/min |
| 3/8" | DN10 | 9.5 mm | 17 – 26 l/min | 3 – 5 l/min |
| 1/2" | DN12 | 12.7 mm | 30 – 46 l/min | 5 – 9 l/min |
| 5/8" | DN16 | 15.9 mm | 48 – 72 l/min | 7 – 14 l/min |
| 3/4" | DN19 | 19.0 mm | 68 – 102 l/min | 10 – 20 l/min |
| 1" | DN25 | 25.4 mm | 122 – 182 l/min | 18 – 36 l/min |
| 1.1/4" | DN31 | 31.8 mm | 190 – 286 l/min | 29 – 57 l/min |
| 1.1/2" | DN38 | 38.1 mm | 274 – 411 l/min | 41 – 82 l/min |
| 2" | DN51 | 50.8 mm | 487 – 730 l/min | 73 – 146 l/min |
The table scrolls horizontally. Values are for guidance; we recommend confirming the size before ordering.
Frequently Asked Questions
How is hydraulic hose size determined?
Hose size is determined by inner diameter and selected against flow rate. Flow velocity should stay between 4 and 6 m/s in pressure lines and between 0.6 and 1.2 m/s in suction lines. Too small a bore causes the oil to heat and pressure to be lost.
How is hydraulic hose length measured?
Length is quoted as the overall dimension from fitting end to fitting end, not the cut length of the hose. Measure between the two connection points with the hose in its installed position, and allow 2–4% because the hose contracts under pressure.
How often should a hydraulic hose be replaced?
Two years is a common interval on lines working under heavy conditions. Regardless of age, however, a hose must be replaced immediately if the cover shows cracks, blisters or exposed wire, if there is weeping around the ferrule, or if it has been permanently crushed.
Why does bend radius matter?
Bending tighter than the catalogue figure breaks the reinforcement wires and the hose bursts at exactly that point. The bend must also not start right at the ferrule outlet — leave at least one hose diameter of straight run.
What safety factor should I use when choosing a hydraulic hose?
The standard safety factor is 4:1, meaning burst pressure is at least four times working pressure. Base the selection on the peak pressure produced when valves close, not on the average system pressure.