Staubli has a range of couplings that can operate in multiple applications as Finishing found out

Most manufacturing plants using compressed air include quick-connect couplings in the circuits, the selection and sizing of these small but important devices is usually not given the consideration deserved. But the effect of poorly chosen couplings can create unexpected problems with productivity, energy conservation, and especially safety. Disconnecting compressed air circuits under pressure can be dangerous, hose whip causes many accidents. This problem can be totally avoided by using Stäubli’s safety connectors as well as associated problems such as repetitive strain injury and ‘white knuckle’. Stäubli’s range of safety compressed air connectors is vast, including high flow and anti scratch couplings, all with an impressive 5 year warranty.
Couplings for compressed air applications are available in several configurations and materials of construction. The choice depends on the specific service requirements. The first decision in the selection of a quick release coupling is choosing an appropriate design for the application involved. There are four important factors to consider: environment, frequency of use, location, and safety.

Couplings used outdoors must be resistant to weather. Those made from copper alloys, malleable iron, stainless steel or aluminum last the longest; plated steel will rust. If the application involves physical abuse or a dirty environment, such as a foundry, the preferred choice would be connectors with no external moving parts, because they are not affected by dirt as much as those with movable sleeves.

Couplings are sized according to two factors; connection size determined by the hose or pipe fitting to which the coupling is connected, and nominal bore size determined by the required airflow. When using couplings with cleaning or dusting devices, the flow rate may not be critical. However, the majority of couplings are used with air tools that require a set pressure at the inlet, a typical plant compressor output is between 7 and 10 bar and the amount of pressure drop allowed at the coupling is usually quite small.

How frequently a quick-connect coupling is used has a direct bearing on the type selected. Axial connect couplings are usually valved and can simply be disconnected. A rotary connect coupling has no valving mechanism. When the need for disconnect arises, the air must be shut off at the source. The most common wear points on valved quick release couplings are the valve, springs, and seals. For heavy-duty use, couplings without spring-loaded, poppet-type valves and with O-ring seals instead of flat washers should be considered.

The position or location of the coupling affects the selection process. If the coupling is at the end of a loose hose, most designs will do. When a coupling is located on a pipe or other fixed location, an automatic connect or zero-pressure type is convenient to use, because only one hand is required to connect or disconnect. When a coupling is located at the end of an overhead hose drop, a zero-pressure type is best because of the lower connection effort required and ease of disengagement without hose whip.

Since air is compressible, release of pressure on disconnection is accompanied by a rapid expansion of air from the unvalved half of the coupling. This release, similar to the action of a rocket engine, causes the hose, if unrestrained, to flail about with the potential for injury. The larger the air volume contained in the hose, the more violent and sustained the action. Hose whip speeds up to 90mph have been recorded, and the plug attached to the hose becomes a dangerous projectile, capable of seriously injuring an operator’s face or eyes. A number of fatalities are recorded each year where hose whip is the cause.

There are two ways to eliminate the problem of hose whip. The downstream coupling half -- the plug -- can be equipped with a ball check valve. When air is released at disconnect, the ball prevents the air from escaping rapidly. A disadvantage of this design is restricted airflow during use. A better alternative is to select a zero-pressure coupling, such as Stäubli’s RCS, this design automatically depressurises the downstream air volume as it shuts off the upstream supply. By the time the coupling is disconnected, there is no residual air pressure remaining to cause hose whip.

Stäubli have several ranges of compressed air, anti hose whip, couplings that provide total safety on disconnecting or connecting under pressure. They are suitable for all types of compressed air lines; typical applications are on pneumatic tools, ring mains, press tools and test benches.

The risk of hose whip is eliminated by Stäubli’s unique two stage disconnection process, which conforms to all the requirements of the anti hose whip regulations in both BS EN 983 and ISO 4414. Decompression is both automatic and instant. On RCS couplings the first push on the disconnect button decompresses the downstream pressure without disconnecting the plug and without any risk to the user. The second push on the button safely releases the depressurised plug from the socket. This automatic connect and disconnect feature allows one-handed operation and there are additional options of a raised push button for use in applications where remote manipulation is being performed or the operator is wearing gloves.

Total operating safety is ensured since it is not possible to open the compressed air circuit unless the plug is in the ‘locked-in’ position. The safety device is integrated into the monobloc locking mechanism and cannot fail. Stäubli’s guarantee of leak tight protection is due to the unique profile of both plug and socket; while other manufacturers only consider the socket profile, Stäubli control both plug and socket to give a high integrity, secure connection.

RCS couplings are compact, lightweight and suitable for all compressed air applications. The air-tight technology, robust construction and quality control ensure a long lasting reliable coupling that Stäubli are prepared to guarantee for 5 years in applications using a matched plug and socket.

A variant of the RCS connector is available in non scratch, high impact composite material with no external metallic parts. This is the ERS range and is suitable for use in applications where any contact could cause scratches, typically in automotive paint and body shops, aircraft assembly and any industry working with the finished product such as furniture, domestic appliances and computers.

Stäubli ADS couplings allow unrestricted full flow, utilising a spherical valve that provides direct flow under full bore conditions resulting in an optimal flow/pressure drop ratio. The locking and isolating functions are separate. Pressure can be shut off from the tool without disconnecting the plug – a very useful feature where pneumatic controls need to be deflated after use.

A covering sleeve controls the air flow in the circuit on the ADS range, cutting off immediately and decompressing the system when pulled backward to expose the release button for final disconnection. The sleeve completely covers the push button release so there is no risk of accidental disconnection. An additional safety device in the socket prevents the plug from being disconnected while the line is still open and in addition the valve cannot be opened while the plug is removed.

Typical applications are on larger air tools requiring a high flow supply, e.g. pneumatic drills, grinders, impact wrenches etc. and also for supplying pneumatic control machinery such as presses and production machines.

Stäubli, have also introduced for use on compressed air lines, a new, unique design, 360° swivel fitting that incorporates a revolutionary double action mechanism. This new mechanism allows full 360° rotation around the centreline, combined with 90° flexibility in the horizontal/vertical plane. The result is a greatly increased work envelope for the connected tool, readily achievable with the minimum of effort. This new generation of swivel is a significant help in reducing the risk of repetitive strain injury or white knuckle to the operator and also preventing damage to the work piece through any use of excessive force.
The swivel has been designed ergonomically to maximise operator efficiency, being incorporated directly in the socket. This results in excellent air flow, perfect leak tightness and a very compact assembly. The design eliminates completely any risk of fold, break or rolling of the hose. It is lightweight and very flexible being manufactured from aluminium and uses air-tight ball bearings.

Other factors also affect the selection and use of couplings. The effect of vibration or shock from tools can be minimised by using a 1metre hose between the tool and coupling, preventing deformation of the plug by impact on the locking balls or pins or elongation of ball bodies in sockets.

Couplings should be checked periodically for leaks in the coupled and uncoupled position. Compressed air leaks are expensive in terms of energy cost and excessive compressor capacity, typically 15-30% of compressed air is lost by leakage between the compressor and the tool. Selection of O-ring seals as fitted to Stäubli connectors instead of washer seals provide a product that lasts longer and is leak free.

Selection of plugs is rarely given the same degree of attention that is allocated to sockets. Many users taking the view that, within reason, any type of plug can be used with any socket. In theory this may be possible; in practice the use of un-matched pairs can seriously affect the performance, reliability and service life of the connector. Stäubli, with their unique plug and socket profile, are prepared to guarantee their connectors for 5 years, in applications using a matched plug and socket.