Clean Break, Flat Face, or Double Shut Off?

How do you know which fluid connector to use for your application?

By Jan Abel, Senior Marketing Communications Manager – North America, Staubli Corporation

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 most 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 allow for a limited amount of spillage on disconnection.

Frequently circuits may need to be connected with fluid left in the line, 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 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, no spillage occurs on connection and disconnection. This type of connector without any space between plug and socket can be more difficult to connect than the double shut off version. However, there are several ways of overcoming this by modifying the internal design of the connector, such as the flat face connectors, rendering it 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 with fluid left in the line.

Single shut off couplings are typically used on compressed air circuits where complete depressurization of the tool side is required to ensure safety, as well as for those circuits where a completely unvalved system is required.

The facility to make a connection with fluid left in the line brings major advantages to many applications where normally the circuit would need to be drained or purged prior to disconnection, then re-pressurized/re-filled afterwards. Typical applications range from the brake lines on F1 Race Cars and the quick replacement of radiators on military vehicles to robot arm tool changers in the automotive sector and mold connections on injection molding machines.

There are many factors that may determine the type of connector selected. These include: the space envelope available, whether the connection is made manually or automatically, mechanical considerations such as temperature, pressure, frequency of operation, and how quickly the connection must be made.

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 depressurize the circuit to allow connection to be made easily and securely.

There are ranges of connectors available with in-built pressure relief systems providing 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, which requires experienced engineers who are trained to fully consider all aspects of the applications 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 minimal maintenance.

• clean break connectors
• double shut off connectors
• flat face connectors
• fluid connector