A custom hydraulic hose should be ordered from the machine’s real operating conditions, not from hose diameter alone. Record maximum working pressure, pressure spikes, flow rate, fluid type, fluid temperature, ambient temperature, hose ID, overall length, end connections, bend radius, movement, and abrasion exposure. ISO 18752:2025 covers pressure classes from 3.5 to 56 MPa and nominal sizes from 5 to 102, while its impulse grades run from 200,000 to 1,000,000 cycles. A 19.1 mm hose, for example, may be rated at 3,500 psi yet require a 96.5 mm minimum bend radius.
Start with pressure because it determines the reinforcement level and limits the fitting system you can use. Normal gauge pressure is not enough: valve closure, actuator reversal, pump pulsation, and rapidly changing loads can briefly raise pressure above the steady reading. The hose, coupling, and crimp combination must therefore be rated for the required working pressure as an assembly.
Burst pressure should never be treated as usable operating pressure. One commercial 19.1 mm SAE 100R16 hose, for example, has a 3,500 psi working rating and a 14,000 psi minimum burst rating, a 4:1 relationship. The same product is rated from -40°F to 212°F. A 14,000 psi burst figure does not make that hose suitable for continuous service above 3,500 psi.
Pressure also has to be considered over time. ISO 18752:2025 classifies hoses by impulse resistance, with Grade A requiring 200,000 cycles, Grade B 500,000 cycles, Grade C 500,000 cycles, and Grade D 1,000,000 cycles. Grade A and B tests are performed at 100°C, while Grades C and D use 120°C; the impulse pressure is generally 133% of maximum working pressure, with specified higher-pressure Grade C classes tested at 120%.
A hose on equipment cycling once every 10 seconds can experience about 2,880 pressure cycles during an 8-hour shift. At 250 working days per year, that is roughly 720,000 cycles before counting startup, shutdown, or irregular machine movements.
That duty profile makes construction important. Braided-wire hoses work well across many medium- and high-pressure systems, while a wire spiral hydraulic hose is commonly considered where high pressure, severe pressure cycling, larger bore sizes, or demanding mobile-equipment service requires multiple reinforcement layers. Construction should still be selected from the applicable manufacturer rating rather than from reinforcement count alone.
Hose diameter comes next because pressure capacity and fluid flow are separate issues. A smaller ID increases fluid velocity at the same flow rate. Parker’s sizing guidance, for example, uses 25 ft/s as the upper recommended velocity shown for pressure-line sizing; at 10 US gal/min, its example moves from a calculated size above -6 to a -8, or 1/2-inch, hose.
| Order input | Information worth supplying |
|---|---|
| Pressure | Normal pressure, maximum pressure, spike conditions |
| Flow | Minimum, normal and maximum gal/min or L/min |
| Size | Hose ID and required connection sizes |
| Fluid | Exact oil, water-glycol or synthetic-fluid name |
| Temperature | Fluid minimum/maximum and ambient minimum/maximum |
| Routing | Length, bend radius, movement and abrasion points |
| Ends | Thread family, size, gender, sealing style and angle |
Once diameter is established, temperature and fluid compatibility need to be checked together. ISO 18752:2025 lists oil-based hydraulic fluids at -40°C to +100°C for AS, AC, BS, and BC hoses and -40°C to +120°C for CS, CC, and DC types. For covered water-based fluids, the stated range is -40°C to +70°C, while water service is 0°C to +70°C.
A supplier therefore needs more detail than “hydraulic oil.” Petroleum oil, phosphate ester, water-glycol fluid, biodegradable hydraulic fluid, and other media can require different tube materials. Temperature ratings can also change with the fluid. A hose located 150 mm from a hot exhaust surface may face an ambient condition very different from a hose carrying the same oil elsewhere on the machine.
Temperature limits also vary substantially among hose families. Gates lists one high-temperature SAE 100R1 hose at -40°F to 275°F continuously and up to 300°F intermittently, while another SAE 100R16 product is listed at -40°F to 212°F. A buyer replacing one with the other based only on diameter and fitting appearance could lose 63°F of continuous-temperature capability.
After pressure, flow, fluid, and temperature have been established, routing determines whether the assembly can actually operate without excessive mechanical stress. Minimum bend radius is measurable and size-specific. A 1-inch Gates 100R16 example uses a 114.3 mm minimum bend radius, while its 1.25-inch version requires 210 mm; increasing ID by 25% in that example raises minimum bend radius by about 84%.
Keep the first bend away from the fitting and avoid installing the hose under tension. Equipment movement should be checked at both ends of the actuator stroke rather than only in the parked position. A hose that looks loose with a cylinder retracted can become tight at full extension, while excess length can create rubbing, looping, or contact with a frame member.
For moving equipment, check at least three positions before confirming length:
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Fully retracted position, including clearance around fittings.
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Mid-stroke position, where a hose loop may move toward another component.
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Fully extended position, including tension, bending and possible twisting.
Fitting identification needs similar care because thread diameter alone cannot distinguish several hydraulic connection families. JIC, ORFS, NPT/NPTF, SAE O-ring boss, BSPP, BSPT, metric threads, and flange connections use different sealing methods. A 90° elbow also needs orientation information; two assemblies can share the same length and fitting part numbers while their elbows are clocked 90° or 180° apart.
Specify the sealing style as well as the thread. JIC connections seal on a flare seat, ORFS uses an O-ring at the face, and SAE O-ring boss seals at the port. Replacing one connection with a visually similar thread can produce poor engagement or leakage even when a wrench appears to tighten it.
Fitting material should follow the environment. Standard plated carbon steel is common on industrial and mobile machinery, while stainless steel may be requested around saltwater, frequent washdown, corrosive chemicals, or equipment where corrosion control is written into the specification. Material should be stated on the purchase order so a later replacement does not silently change the assembly.
Abrasion deserves the same level of attention because external wear can expose reinforcement long before pressure capacity becomes inadequate. Inspect routing near brackets, hose clamps, boom structures, articulation points, and other hoses. If movement creates contact during every cycle, changing the routing or adding a suitable protective sleeve is more useful than ordering the same assembly repeatedly.
On a machine completing 30 cycles per hour for 2,000 operating hours per year, one contact point can be rubbed about 60,000 times annually. The hose specification should therefore include the operating route, not only two end-point measurements.
Cleanliness also belongs on the order when sensitive valves or pumps are involved. Cutting and fitting assembly can leave rubber, metal, or shop debris inside the line. Specify whether the finished hose must be cleaned, capped immediately after cleaning, packaged with end protection, or supplied to a customer-defined contamination requirement.
Testing and documentation should then match the application rather than being added automatically. Some assemblies need proof testing, traceable component records, batch identification, inspection reports, or compliance with SAE, ISO, EN, marine, mining, or equipment-manufacturer requirements. ISO 18752 was revised to its fifth edition in June 2025, so purchase specifications that cite the standard should include the edition when contractual compliance matters.
For repeat orders, assign one controlled assembly number to the completed specification. Store hose type, ID, overall length, fitting numbers, angular orientation, sleeve requirement, test requirement, and revision date under that number. If a fleet replaces 50 identical assemblies per year, removing repeated measuring and thread identification from those 50 maintenance jobs also reduces opportunities for ordering variation.
Before releasing the purchase order, the supplier should be able to read the request without guessing: 3,000 psi working pressure is more useful than “high pressure”; -20°F to 180°F is more useful than “outdoor use”; 18 gal/min is more useful than “normal flow”; and “SAE ORFS female swivel, 90°, clocked 90° from the opposite elbow” is more useful than “elbow fitting.”
The same level of detail should be used for length. State the supplier’s measurement convention, whether length is taken between fitting reference points, and the allowed tolerance. For an assembly that must fit a fixed 750 mm routing envelope, even a 20 mm difference is about 2.7% of total length and can change bend shape, fitting stress, and clearance.
A complete order therefore reads more like an equipment specification than a hose description: operating pressure, expected spike conditions, flow rate, ID, exact fluid, temperature range, hose construction, full fitting identification, fitting material, overall length, elbow orientation, minimum routing radius, movement, abrasion protection, cleanliness, testing, applicable standard, and quantity. Supplying those values gives the manufacturer enough information to build the same assembly again rather than recreate it from an old hose.