Hose Assemblies

Choosing the right hose assembly is crucial for safe and economical operation of a hydraulic system. Criteria include:

• Compatibility with the medium—including cleaning processes
• Temperature resistance—check pressure–temperature behavior
• Specific environmental conditions and external influences
• Pressure resistance including required safety factors (also vacuum behavior)
• Nominal sizes and resulting flow velocities
• Bending radii
• Changes in length and outer diameter
• Special stresses from external forces or pressure impulses
• Abrasion behavior and possible protection
• Availability of hose material and fittings
• Installation conditions such as movement cycles, kinking, whipping, marking, swivel angles of elbows, leg lengths
• Secure sealing forms (seal head design)
• Required approvals

Note: Operating conditions combining maximum pressure, maximum temperature and minimum bending radius will shorten the service life of hose assemblies!

Always verify compatibility of hose and fitting materials with conveyed media. Consider surrounding media in selection.

Consider expected operating and ambient temperatures when selecting a hose assembly. Using hoses outside their permissible temperature range will significantly shorten service life. Valid data can be found in the respective datasheets.

Note that the outer layer of a rubber hose is susceptible to environmental influences like ozone or strong UV radiation. Ozone and UV can break the polymer chains of the elastomer, causing loss of elasticity, hardening and brittleness, leading to radial cracks extending to the reinforcement, especially on outer bends.

Maximum working pressure (dynamic working pressure) determines hose construction and selection. Depending on application, hoses with textile braid, wire braid, spiral wire reinforcement or special metal/PTFE hoses are available.

The inner diameter of hose or pipe is critical in hydraulic systems. Fluid flow incurs pressure loss, depending on flow type, wall roughness, length, inner diameter, fluid density and velocity. Also consider “run-up length” affecting velocity profile. Pressure losses also occur through fittings, valves, bends and other restrictions.

Generally, to minimize losses choose a sufficiently large inner diameter or flow cross-section. When in doubt, select the next larger size to reduce flow velocity and pressure loss.

If a hose assembly is installed with twist, service life is markedly reduced by internal abrasion of the reinforcements. Under impulse pressure, the reinforcement strives to return to its neutral position. Special stress occurs at attachment points.

Note: As a rule of thumb, 7° twist reduces service life by 80%. Ensure no twist occurs during installation, e.g. when tightening the swivel nut.

Each hose type has a specified minimum bend radius by nominal size. Undershooting it reduces service life and load capacity: on the outside bend, gaps in the braid can cause oil seepage; on the inside bend, reinforcement is compressed and loses pressure capacity. This typically occurs immediately behind the fitting when sharply bent.

If installation permits, introduce bends after a straight run equal to 1.5 × outer diameter. If not, use kink guards or similar.

Sometimes, using appropriate fittings can prevent undershooting the minimum radius. As shown above, an angled fitting creates a sufficient bend. Fittings are standard at 45°, 90° and straight; others on request.

Routing over an edge may abrade the outer layer due to hose movement. Likewise, hoses too close together rub each other. The braid then loses corrosion protection, risking failure. If abrasion cannot be avoided, use hoses with high-abrasion outer covers.

Avoid tensile stresses on hose assemblies as they endanger fittings. Note that hoses shorten under pressure (up to 4 % at max pressure), so always install with some slack. Account for movement cycles.

Note: In some cases (e.g. spring‐loaded rollers) tensile stress is unavoidable; permissible loads must then be agreed with HANSA-FLEX.

Avoid clamps that impede natural movement and length changes. Friction in clamping destroys the outer layer over time. Fit clamps only on straight runs.

If hose failure could cause dangerous whipping, restrain or shield the hose. The HANSA-FLEX Stopflex safety system provides a secure connection between hose and machine.

If hose failure could release fluid hazardously, shield the hose accordingly.

Despite cross-linking, rubber can creep between nipple and fitting. This viscoelastic behavior leads to leaks or fitting migration. Peeling the outer rubber layer in the prescribed area minimizes this risk.

When selecting hoses, consider permeation or effusion of gas molecules through the inner layer. Media loss or unwanted concentrations of flammable, explosive or toxic gases may result. Perforating the outer layer (“pricking”) to vent gases is used, e.g. for air lines above 16 bar.