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IT’S FITTING, ISN’T IT?
Quick-disconnect hose fittings are a growing part of our business.
WHERE THE BUCK STOPS: Rick Hudson is
founder
and CEO of RL Hudson.
by Rick Hudson
Some customers have asked about quick-disconnect couplings for hose.The idea seems simple: just slide a tube through a snug-fitting O-ring that’s mounted inside a slightly larger tube, and hold it in place with a locking mechanism. It turns out that there’s much more to it.
Quick disconnect hose couplings, also called quick action, quick connect, or quick-release couplings, are designed for just one purpose: to be easily and quickly disconnected and reconnected, as many times as necessary. Some are also designed to minimize or eliminate any loss of fluid during disconnection and any entrapment of air during connection.
A common, yet demanding, application for quick disconnect hose couplings is hydraulic systems, particularly those that must accommodate the repeated removal and installation of attachments and auxiliary systems.Construction equipment and farm implements are usually equipped with quick disconnect hydraulic couplings.
Other quick disconnect applications can be found in pneumatic, water, liquid and gaseous fuel, lubrication, vacuum, and refrigerant systems. Examples include auxiliary fuel tanks for marine use, irrigation systems, pump-driven sprayers, and air or hydraulic-powered hand tools.
Here are some terms you might hear in connection with quick disconnect hose couplings:
INTERCHANGE COUPLING: As you might imagine, there is an enormous variety of different coupling designs, most of which will only work when both components have the same design. In part because of the rise of international trade in equipment, an ISO standard has been written to increase interchangeability among different manufacturers’ couplings. Many ISO interchange couplings are now available, as are non- ISO couplings that will interchange with specific brands, depending on the application.
DRYBREAK COUPLING: This type is also referred to as “dry disconnect,” “no-spill,” “flat face,” or “flush face.” In many applications, for safety or environmental reasons, the conveyed fluid must not be released during connection or disconnection. Drybreak couplings, which have a characteristic “flush face” appearance when disconnected, minimize or eliminate fluid release while providing virtually no air inclusion during reconnection.
POPPET VALVE COUPLING: With certain exceptions, one or both ends of a coupling must stop the flow of fluid when the coupling is separated. The poppet valve is a simple spring-loaded disc with an elastomeric sealing surface. It is usually located in the female half. When the male half is withdrawn, the spring pushes the poppet valve closed. Effective and easily manufactured, poppet valve hose couplings are used in more applications than any other style of coupling.
BALL CONNECTOR: A very common and effective locking system consists of a number of steel balls in the body of the female half.When the coupling is locked, the balls are pushed into a groove in the male half by a springloaded, ramped sleeve on the female half.When the sleeve is pulled back, the balls are free to move outward, releasing the male half. This basic approach lends itself to a large variety of designs and applications.
TWIST-LOCK: The male and female halves are designed to be brought together (often against valve spring force), then twisted in relation to each other to engage multiple hooks, dogs, or protrusions. This type may also be called “bayonet” or “crowfoot” style. In a variation of this design, the connectors have flat sealing faces, one of which usually contains an O-ring, and which are placed at right angles to the hose. The sealing faces are brought together with the hoses held in a shallow “V,” then the coupling is straightened to engage the locks and compress the O-ring.
THREADED (THREAD-TO-CONNECT) COUPLING: Where high pressure and high flow are more important than ease of use, threaded couplings may be specified. Such couplings use a male thread on one end and a female threaded sleeve on the other.To form a connection, the sleeve is turned until the male threads are fully engaged.Many designs permit hand tightening.
CAMLOCK COUPLING: Similar in concept to the ball connector, camlock couplings use two pivoting levers that end in cams.When the coupling is connected, the levers are moved to cause the cams—which are typically on the female half—to engage a groove in the male half.Camlock couplings are often found in larger-diameter applications.
SINGLE OR DOUBLE SHUT-OFF: Depending on the application, the male half, the female half, or both halves of the coupling will be equipped with automatic or manual valves (shut-offs). Most (but not all) manual shut-offs are interlocked to prevent their being opened when the coupling has been disconnected. Non-valved couplings do not have shut-off valves.
CONNECT-UNDER-PRESSURE COUPLING: Although nearly any quick disconnect coupling can be connected under moderate pressure, higher pressures, such as those in a live hydraulic system,may make it necessary to use a special pressure- relieving design. Another alternative is a hand- or wrench-tightened threaded coupling.
HIGH FLOW COUPLING: This is a general term for any coupling that provides lower flow restriction, size for size, than conventional designs allow.
The enormous range of possible uses for quick disconnect couplings means many choices in body, valve, spring, and seal materials. Common body materials include brass, bronze, aluminum, polypropylene, nylon, acetal, steel (often hardened), and stainless steel. Plastic materials may be reinforced with glass fiber to add strength. For special applications, fluoroplastics or PEEK (polyetheretherketone) may be specified.
Springs are usually steel or stainless steel, while seal material choices include Buna-N (nitrile), ethylene propylene (EPDM), polyurethane, fluoroelastomer, and silicone. Locking balls are hardened steel or stainless steel.
Quick disconnect couplings are available in nominal inside diameters from 1/8” to 6” and in metric sizes. Working pressures can range from vacuum to 40,000 psi, depending upon the design. Couplings are available with male or female pipe threads, bolting flanges, one of several types of hose connections (barbed, internal expansion, or external compression), or a non-standard thread.
A final design variation is the availability of some means of locking the coupling against unintended disconnection.
QUICK-DISCONNECT COUPLING SELECTION CHECKLIST:
For many applications, such as injection mold cooling or small pneumatic tool air supply, it’s simply a matter of choosing one of only a few standard fittings. In many other applications, you should ask one or more of these questions:
- What fluid(s) will the coupling be exposed to?
- What is the working pressure? What is the maximum (impulse) pressure?
- What is the working temperature range? The maximum temperature?
- How much flow restriction or pressure drop is acceptable?
- No shut-off, single side shut-off, or two-side shut-off? If single side, which side?
- Is the application static, or will one or both ends be moving or rotating?
- Does the application include connecting or disconnecting under pressure?
- How much fluid loss (if any) is acceptable on disconnection?
- How much air entrapment (if any) is acceptable on connection?
- How much leakage (if any) is acceptable during use?
- What must the end configurations be?
- Is an industry interchange coupling required?
- How many connections/disconnections must the coupling withstand without leakage or other functional problems?
IN CLOSING As you can see, the choices are many, but you can count on RL Hudson to help you make the right choice. And if your application calls for something out of the ordinary, we hope you will give us the opportunity to design, prototype, and test a quick disconnect coupling that will meet or exceed your requirements.
