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Connectors: clean break, flat face or double shut off?

Connectors: clean break, flat face or double shut off?

Spill free, clean break, flat face, double shut off, single shut off are just some of the options available when selecting quick connectors. But how do they differ and what benefits do they bring? Craig Forrester of Stäubli Connectors explains.

Quick release couplings should provide an easy to use, fast and reliable method of connection and disconnection that performs faultlessly through many connection cycles. Although all connectors are designed to be leak free both in the connected and disconnected state many specific applications also need to guarantee no spillage at all; for example connectors used in cooling circuits for electronics or circuits containing hazardous substances. Other applications in less sensitive environments or on circuits containing harmless materials a limited amount of spillage on disconnection may be acceptable.

Frequently circuits may need to be connected while still under pressure, avoiding the time and cost of purging the system. Other applications need to maintain the integrity of the circuit, preventing any ingress of air or contaminants. Fortunately there are designs of quick connectors that satisfy each of these diverse and challenging requirements.

Spillage is often a misunderstood feature of quick connectors. A double shut off design of connector will not prevent a limited amount of spillage on disconnection. This is due to the gap between the valve on each side of the connector (plug and socket); whatever liquid or gas occupies the space between the valves will be the volume spilled on disconnection.

For many applications even this limited degree of spillage would be unacceptable and a quick connector that avoids this problem completely is required. Flat face connectors provide the solution. Flat face connectors are designed to ensure that the plug and socket faces match together closely, there is no space between them for any liquid or gas to be retained, and consequently on connection and disconnection no spillage occurs. This type of connector without any space between plug and socket can be more difficult to connect than the double shut off version. There are several ways of overcoming this by modification to the internal design of the connector; St_ubli's R&D experts have evolved techniques that make flat face connectors as easy to connect as double shut off versions.

Flat face connectors also maintain circuit integrity on connection and disconnection. The close fit between plug and socket faces removes any space for air or other contaminants to enter the circuit even when connecting or disconnecting under pressure. Single shut off couplings are typically used on compressed air circuits where complete depressurisation of the tool side is required to ensure safety; and for those circuits where a completely unvalved system is required.

The facility to make a connection under pressure brings major advantages to many applications where normally the circuit would need to be drained or purged prior to disconnection and then re-pressurised/re-filled afterwards. Typical applications range from the brake lines on F1 racecars and the quick replacement of radiators on military vehicles, to robot arm tool changers in the automotive sector and mould connections on injection moulding machines. The type of connector selected will depend on many factors, for example the space envelope available, if the connection is made manually or automatically, mechanical considerations such as vibration, temperature and pressure as well as the frequency and speed of connection.

Many hydraulic circuits may retain residual pressure in the circuit after the planned operation has been completed. This can cause significant problems with connecting especially where standard hydraulic connectors have been used. Standard connectors do not incorporate a pressure relief mechanism that will depressurise the circuit to allow connection to be made easily and securely.

Stäubli's range of connectors with in-built pressure relief systems provides the solution. A central relief valve automatically opens on connection, safely releasing the volume of fluid necessary to allow the backward movement of the valve permitting easy connection. The connector is undamaged and the circuit integrity is maintained.  

Selecting the appropriate quick connector calls for evaluation of many parameters in the planned application. Frequently companies rely on the experience of Stäubli engineers who are trained to fully consider all aspects of the application and are skilled in evaluating the combination of requirements.  They will provide advice from the design stage onwards on the most suitable connection solution for any application to ensure excellent performance, long term reliability and requiring the minimum of maintenance.

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