Capacidad de retención de agua

Many accessories and additional components are sometimes used with hose assemblies in order to protect them from abra-sions, extreme temperatures and irradiation, for safety reasons, for fire protection, etc.

Let’s see the most common types of protection the selection criteria and the methods used to solve routing and protection problems.

Bundling (fig. 1).

When installing hose assemblies, various bundling techniques can improve space utilisation, appearance and hose life. Here are some tips:

• Group and bundle similarly constructed and sized hose together using clamp blocks, nylon straps or nylon sleeving or plastic spring guards;

• Always consider mechanical movement when bundling.

Allow sufficient slack without pulling on a fitting or another hose. Bundles (like individual hoses) should bend in one plane only;

• Avoid to bundle high-pressure hoses with low-pressure hoses: under pressure, they can work against each other;

• Bundling rubber hose with thermoplastic or PTFE hose should be avoided.

Sleeving

There are numerous sleeving types used today. The most com-mon is nylon (fig. 2), which is typically used for one or more of the following applications:

• to protect hose from abrasion;

• for use in bundling;

• to protect equipment and operators from injury due to hose failure (fluid jet dispersion).

Spring guard

There are many type of spring guards: flat armour, plated wire, plastic, etc. They can be used to bundle hoses or provide sta-bility and/or protection against abrasion. Tightly wound plate wire guards can also be used as bend restrictors to ease stress on the hose (fig. 3).

Bend restrictors

Bend restrictors typically are PVC or steel sleeves which are installed near the coupling during hose assembly. They reduce bending stress in the hose near the coupling to prevent dam-age (fig. 4).

Clamps

Clamps are used to fix the assemblies to the system/equipment and avoid potential contacts with high temperature surfaces, reduce vibration and risk of unintended movements (fig. 5).

A wide range of clamp types and quality is available on the

fig. 1 - Bundling

fig. 2 - Sleeving

fig. 3 - Spring guard

fig. 4 - Bend restrictor

fig. 5 - Clamps

132

market: with rubber hoses, the use of special clamps with internal soft rubber rings in contact with the hose cover is advisable. These clamps considerably reduce the risk of abrasion on the hose cover, even in presence of vibrations, dust, etc.

Manuli Rubber Industries has experience with some of the top quality level of clamps (fig. 6); contact Manuli Rubber Industries for detailed recommendations.

Some useful tips for the installation of clamps and assemblies are the following:

• choose clamp bore close to the hose OD, without crimping it:

- the hose should “breath” under pressure;

- the hose should adjust its configuration.

• for safety reasons, position the clamps to reduce the possi-bility of “whiplash” in case of fitting blow-off;

• “soft” rubber insert between clamps structures is always advisable to reduce vibrations transmission and cover wear (the rubber insert has to be “sacrificial”).

Safety restraint systems (whipcheck and guards/shields) Restraint systems such as whipchecks and protection shields are used to fulfil the safety requirements of the hydraulic systems and equipment, in particular when there is risk of injury to operators and personnel working near the equipment.

Restraint systems are used:

• in hydraulics applications when there are safety aspects involved in a potential failure of the assembly, mainly blow-off of the fitting: we recommend STOPFLEX type;

• always with compressed air and with gas applications in general (e.g. EQUATOR hose with compressed air), due to the hazard connected with the potential “whiplash” of the hose disconnected from the fitting, we recommended WHIPCHECK type, double connection rings.

When the equipment-designers identify an hazardous condi-tion where the risk can be contained using restraint systems or shields, different International Specification can be followed as reference.

• For example, refer to - International Standard ISO 3457 (earth-moving machinery - guards and shields - definitions and specifications) – Point 4.9: “Where hoses are used oper-ating to a pressure of at least 50 bar and/or at temperature of at least 50°C, and are located within 0,5 m of the operator, deflecting shield should be provided to protect the operator from thesudden hose failure.

The shield should be sufficiently sturdy to stop or divert fluids away from the operator.”

133

• ISO 4413 "Hydraulic fluid power - General rules relating to systems" point 9.5.3 Protection against failure (of hose assemblies) reports: "If the failure of a hose assembly consti-tutes a whiplash hazard, the hose assembly shall be restrained or shielded. If the failure of a hose assembly con-stitutes a fluid ejection or fire hazard, it shall be shielded." The need of restraint systems or shields on the hose assemblies depends on the evaluation of the impact on safety of each assembly in the equipment by the equipment designers.

• EN 982 "Safety of machinery - Safety requirements for fluid power systems and their components - Hydraulics" is the

“armonized” safety specification in Europe. Point 5.3.4.3.2 Failure (of flexible hose assemblies) states: "If the failure of a flexible hose assembly constitutes a whiplash hazard, it shall be restrained or shielded. If the failure of a flexible hose assembly constitutes a fluid ejection hazard, it shall be shielded."

• EN 982 describes also the safety requirements for flexible hose assemblies in the chapter 5.3.4.3:“Flexible hose assem-blies shall fulfil all performance requirements specified in the appropriate European and/or international standard(s)”. This means that hose assemblies on a machines must meet the SAE, ISO and EN requirements and must have a record for qualifications and production control tests, to be complying with the European Machinery Directive 98/37/CE.

• Similar requirement and recommendations are reported by the SAE J1273 specification, par. 4.2 Whipping hose (safety considerations): "If a pressurised hose assembly blows apart, the fittings can be thrown off at high speed and the loose hose can flail or whip with great force. When this risk exists, consider guards and restraints to protect against injury." Also in this case the requirement of the restraint systems for hose assemblies would be subjected to the system designer risk evaluation.

The restraint system with steel ferrule crimped on the hose are not recommended, due to the risk to involve hose deformation, cover bubbles, etc. since the hose body must be free to “breath” under pressure. Manuli recommends the use of restraint systems with internal rubber ring in contact with the hose cover or steel cords (e.g. STOPFLEX).

fig. 6 - Clamp with rubber ring

fig. 7 - Whipcheck double eys

fig. 8 - Protective shields

Safety is of maximum importance when designing hydraulic circuits, especially when considering the high pressure lines.

In Europe the reference legislation is the European Machinery Directive 98/37/CE, that requires at the point 1.5.3. “Where machinery is powered by an energy other than electricity (e.g.

hydraulic, pneumatic or thermal energy, etc.), it must be so designed, constructed and equipped as to avoid all potential hazards associated with these types of energy.”

The European standard EN 982 - “Safety of machinery - safety requirements for fluid power systems and their components -hydraulics,” lists possible hazards associated with the use of hydraulic power in a machine:

• mechanical hazards (e.g. coupling blow-off, whipping hose, hose burst, pinhole in hose);

• thermal hazards (e.g. fluid high temperature) can heat metal parts such as couplings and adaptors, causing severe burns when touched by someone;

• unintended movements caused by electromagnetic fields;

• hazards resulting from contact with, or inhalation of, harmful fluids, gases, mists, fumes and dusts;

• fire or explosion hazards;

• hazards caused by failure of energy supply, breaking down of machinery parts and other functional disorders (e.g.

falling or ejecting of moving parts or pieces held by the machinery, unexpected start, etc.).

134