COUPLINGS SELECTION CRITERIA

Several factors, such as thread end compatibility, pressure and mechanical resistance, corrosion resistance, vibration, temperature, use of adaptors, fluid compatibility, etc. must be considered when selecting a coupling for an application or system/equipment.

Thread end and sealing surface compatibility

Thread ends must be compatible in order to prevent leaking or failure. Three elements must be considered in particular:

thread interface, seat angles and eventual O-Rings. It is critical that both the male and female fittings are compatible to ensure an effective seal. Incorrect sealing will cause leaks, which can represent a safety and environmental hazard.

Temperature

Metal surfaces can expand and contract under extreme tem-perature fluctuations. Selecting couplings with O-Rings, will give a better sealing even with metal components deformations.

It may be necessary to use O-Ring materials that are suitable for high temperatures and chemically compatible with the working fluid at the requested temperature. If the application is at high temperature, it is advisable to avoid brass or aluminium fittings.

Fluid compatibility

It is common practice to select hoses taking particular care of the compatibility with the working fluid, it is far less common to do so for couplings.. Also couplings, however, can also be affected by fluids, in particular aggressive fluids. Always check the fluid compatibility chart for coupling and O-Ring materials and contact Manuli for specific details or doubts.

Corrosion resistance

Most hydraulic fittings are manufactured from carbon steel and have zinc plating external treatment for corrosion resist-ance. Even if the high performance of the Manuli couplings treatment pass 400 hours before red corrosion in the standard salt spray tests (ASTM B117), other materials such as stainless steel can be necessary for special applications (marine equip-ment, mining, etc.).

Working pressure

Working pressure should be a relevant consideration when selecting a fitting. Some fittings do not seal well at high pres-sures and can cause leaks. O-Ring type fittings as well as solid port connectors work well at high pressures. It is important to make sure that not only the maximum rated working pressure is higher than the working pressure of the system but also that the architecture (thread type, sealing surfaces, thicknesses, shape of the connection, etc.) of the termination end is suit-able for the intended use.

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Vibrations

Hose flexing conditions and/or vibrations at the end connec-tion, can potentially weaken or reduce the connection capa-bility. It is important to select couplings accordingly: flanges or other couplings with O-Ring for sealing perform better under vibration, avoid use of couplings that seal on the threads.

Couplings thread style and pressure performance

The couplings termination ends are realised according to the reference international specifications, that define the thread type, sealing surfaces angles and type, architecture of the ter-mination end, etc.

Manuli couplings product range presents a wide variety of the most common termination end types, offering also some global OEM (Original Equipment Manufacturer) special con-nections and upon request even personalised solutions.

Among the others we can mention:

BSP (British Standard Pipe) standard connections:

• Male BSPP (Parallel) and BSPT (Tapered)

• BSP 60°

• BSP O-Ring 60°

• BSP flat seat

DIN (Deutsches Institut für Normung) standard connec-tions:

• DIN standpipe

• DIN Metric 60°

• DIN Multiseal

• DIN Metric 24° (light and heavy series)

SAE (Society of Automotive Engineers) standard connec-tions:

• JIC (Joint Industrial Council) connections

• ORFS (O-Ring Face Seal) connections

• SAE connections (90° cone)

• NPTF (National Pipe Tapered Fuel) and NPSM (National Pipe Straight Mechanical) connections

• SAE flanges (3000 and 6000 psi)

• STAPLE LOCK connections

NF (Norme Française) standard connections:

• 24° metric connections

• 24° gaz connections

JIS (Japanese Industrial Standard) standard connections The following table is a summary (exceeding international specifications) of hydraulic pressure performance by thread style and size for coupling termination ends.

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The table is intended only as an approximate guide to field performance of products, figures shown are maximum oper-ating pressures in bar, based upon a 4:1 safety factor relative to the connection minimum burst pressure. Testing of Manuli fittings range confirm the data; anyway the robustness and high quality of the Manuli fittings generally exceed the mentioned performance. Testing was conducted at the recommended assembly torque in hardened test blocks.

The pressure rating of the hose assembly, complete of all the components, including fittings and adapters, must be defined as the rate of the weakest component.

Selecting a termination end for a given hose, means also a proper choice of the type, architecture and pressure rate com-patible with the hose one.

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Coupling termination end type

Max. Working pressure (bar)

Termination end type BSP Male

O-Ring BSP Female BSP Female Multiseal DIN Female Metric 60° DIN Female Metric Male 24° L Series Metric Female 24° L Series Metric Male 24° Heavy Series Metric Female 24° Heavy Series Millimetric Metric Male Millimetric Metric Female Metric Gaz Male Metric Gaz Female JIS Metric Female JIS Gas Female JIC 37° SAE Male CODE 61 SAE Flanges CODE 62 SAE Flanges XTRAFLANGES

WASH CLEANER FEMALE (M24913)

Ref. Specification BS5200 - ISO WD8434-6 BS5200 - ISO WD8434-6 BS5200 - ISO WD8434-6 DIN 20066/Febr.'82 DIN 20066/Febr.'82 DIN 20066/Oct. '02 DIN 20066/Oct. '02 DIN 20066/Oct. '02 DIN 20066/Oct. '02 NORM. FRANC. E48-064 NORM. FRANC. E48-064 NORM. FRANC. E48-064 NORM. FRANC. E48-064 JIS B8363 Hose size / Dash

DN

Additional considerations on termination ends selection Some useful considerations as support to the termination ends selection, for a proper use in the requested application.

The fittings working pressures suggested by the international specifications are the most important guideline to select the right termination end: working pressure of the hose assembly must be the lowest level between hose and fitting ones. Fitting working pressure should be selected higher or equal to the hose one.

But also other considerations are relevant.

For heavy duty applications, in presence of vibrations, high fatigue mission profiles and/or large size hoses, flanges are often preferable compared to other termination ends. When this is not possible, other robust termination ends can be selected, such as DIN Metric heavy series and ORFS.

The recommendation in favour of safety is to avoid selection of low-pressure termination ends for hose assemblies dedicated to the most severe mission profiles. Even thought the market requires the maximum availability of many different termina-tion end types (for example medium pressure terminatermina-tion end for InterLock fittings dedicated to heavy duty wire spiral hoses) these should not be interpreted as optimum solutions.

In addition, O-Ring type termination ends are always to be pre-ferred for new projects, as also declared by the international specifications ISO, SAE, etc. for their better performance com-pared to the traditional metal to metal sealing types. Standard O-Ring supplied are generally NBR based, suitable up to max.

temperature of 125°C as from the international specifications;

for eventual special applications different types of O-Rings could be necessary, with a more appropriate compound, con-sidering chemical compatibility with service fluid and tempera-ture resistance.

For any doubt and specific advice, contact Manuli Rubber Industries specialists.

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