Basic knowledge of quick coupling

If the hoses or tubes in the fluid power system are connected and disconnected more frequently than once a week, the quick couplings are likely to quickly pay for themselves by increasing productivity.

Although the concept is simple, many quick couplings are precisely designed for specific fluid applications. Their extensive use over the years has produced a variety of designs, not only for specific, but also for general industrial applications.

Therefore, there may be uncertainty as to whether a particular design is best for a given application.

Regardless of the manufacturer, all quick connectors have something in common. There are two parts: plug and socket. The plug is half of the male and the socket is half of the female. When properly connected, these components can effectively seal and lock the joint to control internal pressure and resist any tension that tends to pull the joint apart. By disengaging the locking mechanism and separating the parts, the parts can be easily disconnected without tools.

Where to use them?

A common application is in assembly workstations, where workers may have to quickly switch from impact wrenches to drilling machines to riveting machines. There is a quick coupling on each tool and a mating part on the air pipeline, and tool replacement can be completed in a few seconds. If there is no coupling, each tool needs a separate air line; a large number of tool

On hydraulic test benches, quick couplings eliminate bottlenecks by reducing the time required to test each component. Just push/pull quickly and the component can be tested. In contrast, if technicians have to use accessories and wrenches to enter the system in each test procedure, the test time will skyrocket

TOPA Valve layout

In many different quick connector designs, either of the two types are used for the application. The advantage of the valveless type is that the pressure loss through the coupling is low, but once the coupling is disconnected, it cannot prevent fluid from escaping. However, if the pressure drop in the system must be kept to a minimum and the fluid drained from the disconnected hose can be tolerated, a valveless joint may be the designer's first choice.

Obviously, for all applications, a coupling that does not leak when disconnected will be the first choice-all other factors are the same. Incorporate a shut-off valve into one or two halves of the coupling, and only when the two halves are connected, fluid can flow through the coupling. When the coupling is disconnected, the mechanical connection between the two halves of the coupling is broken and causes the valve to close, thereby preventing flow.

When only one half of the coupling is equipped with a valve, it is usually located at the source (upstream) end of the joint. Pneumatic systems usually use this arrangement: the valved coupling half prevents air loss in the system when the joint is disconnected, and the unvalved coupling half allows downstream air to escape.

In hydraulic applications, both coupling halves are usually equipped with valves. This approach not only minimizes fluid leakage, but also limits the amount of air, dirt, and water that can enter the system. When the joint is disconnected, air will be trapped between the valves and enter the system when the joint is reconnected.

Therefore, if the hydraulic system cannot tolerate air inclusions, special measures may be required to remove the air. In order to solve these problems, many manufacturers now provide flat joints, which can reduce fluid spillage to one drop or less every time the joint is disconnected. In addition, when the coupling is disconnected, the mating surface of each coupling half is flush. This minimizes the ingress of air and wipes the mating surface clean before reconnecting.

Valve precautions

Although these valved designs provide the convenience of controlling fluid loss, there are also trade-offs. First, compared to valveless designs, valved couplings can produce significantly higher pressure drops. The amount of this loss depends on the coupling size and design. The pressure drop can be slightly reduced by increasing the size of the coupling. There may also be some deviations in pressure drop from one coupling design to another. If pressure drop is an issue, be sure to check the manufacturer's literature for appropriate data.

Other disadvantages of valve couplings include larger size and higher cost. The cost difference will vary depending on the size and personal design. Generally, couplings designed for low pressure drop, no fluid leakage, and no air entrapment are more expensive. However, the manufacturer pointed out that the increased productivity by not having to clean up the spilled liquid has offset the price difference.

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