Making the connection

Oct. 13, 2010
Quick-acting couplings improve productivity in hydraulic systems that require frequent connectioning and disconnectioning.
If a hose or tube in a fluid power system will be connected and disconnected frequently, chances are a quick-acting coupling will improve productivity. Although simple in concept, many quick-acting couplings are precisely engineered for specific fluid applications. Their widespread use has yielded a diverse variety of designs to serve not only specific, but general industrial applications as well. Consequently, uncertainty can arise as to whether a specific deign is best for a given application.

All quick-acting couplings have some elements in common. All have two parts: a plug (the male half) and a socket (the female half). When connected properly, they seal and lock the joint to contain internal pressures and resist tensile forces that tend to pull the joint apart. The parts are easily disconnected without tools by disengaging a locking mechanism and separating parts.

The more frequently hoses must be connected and disconnected, the more valuable quick-acting couplings become. They also become more critical as machine productivity increases. On hydraulic test stands, quick-acting couplings eliminate bottlenecks by slashing the time required to test each assembly. Test time is slashed with a quick push/pull, instead of tapping into systems using fittings and a wrench.

Valve arrangements

Among the different designs of quick-acting couplings, either of two types are used for an application. Unvalved types have the advantage of low pressure loss through the coupling but do not prevent fluid from escaping once it is disconnected. However, if pressure drop in the system must be held to a minimum, and fluid draining from disconnected hoses can be tolerated, unvalved couplings could be used.

Obviously, a coupling that does not leak when disconnected is preferred. Incorporating a shutoff valve into one or both halves of the coupling allows fluid to flow through the coupling only when both halves are connected. When the coupling is disconnected, a mechanical link between the coupling halves is broken and causes the valve to close, blocking flow.

Both coupling halves usually are valved, which minimizes fluid leakage and limits the amount of air, dirt, and water that enter the system. When a coupling is disconnected, air can become trapped between valves and enter the system when the joint is reconnected. If the system cannot tolerate air inclusion, special provisions may be needed to exclude air. As a result, many manufacturers offer flat-faced couplings that reduce fluid spillage to a drop or less every time the coupling is disconnected. Mating surfaces of each coupling half are flush when the coupling is disconnected, minimizing air ingression.

Valve considerations

While valved designs offer controlled fluid loss, there are trade-offs. Valved couplings can generate a much higher pressure drop than unvalved designs. The amount of this loss depends on coupling size and design. Pressure drop can be reduced by oversizing the coupling. There also may be some deviation in pressure drop from one coupling design to another.

Other drawbacks to valved couplings include larger size and higher cost. Generally, couplings designed for low pressure drop, no fluid leakage, and no air entrapment carry a higher price tag. The price differential can be offset by higher productivity gained by not having to clean up fluid spills.

Criteria to consider in selection

Before selecting a coupling, its expected performance and fluid medium must be considered. For example, what fluid will flow through the coupling? Characteristics of the fluid — viscosity, corrosiveness — will influence the type of coupling to be used. Other questions concerning fluid deal with temperature (high, low, or wide variation), pressure, and flow rate.

The coupling’s construction shoud also be taken into consideration. How often will it be connected and disconnected? What type and diameter of hose or tubing will be used? Will the coupling or hose be subjected to abuse such as impact from falling objects, severe vibration, or contamination?

Once these questions have been answered, a preliminary selection of coupling can be made: one, two, or no shutoff valves, and the type of connect/disconnect mechanism.

Materials of construction are another consideration. Most O-ring and seal materials accommodate fluids at a wide range of temperatures. Plug and socket material also is important. Steel, stainless steel, and brass are common. Many parts are also made from carbon steel and plated with a corrosion-resistant metal to keep material costs down.

Plastic may be used for fluid transfer if pressure, temperature, and chemical environment permit. Remember that plastic couplings may contain internal metal components that can be corroded by certain hydraulic fluids.

Pressure rating relates to values that provide optimum service life and maximum pressure that can be tolerated without failure. Literature should include data for determining pressure drop through the coupling at expected flows and pressures. Many of these calculations are based on flow of water at 60° F. Remember, pressure drop for oil will be higher because of its higher viscosity. Precise valves for pressure drop for specific couplings should be obtained from the manufacturer.

Couplings may be subjected to pressures well above maximum operating pressure. Sudden shifting of valves or abrupt application of heavy loads can cause system pressure to rise and fall within milliseconds. These pressure spikes often go undetected, but still can damage seals and locking elements of the coupling. The coupling can develop leaks and become difficult to disconnect or reconnect. To prevent this, select a coupling with a pressure rating substantially higher than the anticipated maximum operating pressure.

Couplings may be subjected to vibration or relative rotation between the mating halves while pressurized. Often, these conditions will shorten the coupling’s expected life by causing leakage or difficulties in connecting or disconnecting. Therefore, check with the manufacturer to determine if the coupling will tolerate these conditions.

Below is a list of companies that supply quick-acting couplings.

Airmo Inc., Coon Rapids, MN, (800) 394-0016,
Automation Direct, Cumming, GA, (800) 633-0405, Industrial Corp., Gurnee, IL, (847) 263-7200,
Colder Products Co., St. Paul, MN, (651) 645-0091, [email protected],
Eaton Corp., Eden Prairie, MN, (952) 937-9800,
Europower Inc., Valley View, OH, (216) 447-0898, [email protected],
Fairview Fittings & Mfg. Inc., Wheatfield, NY, (716) 614-0320, [email protected],
Faster Inc., Maumee, OH, (419) 868-8197, [email protected],
FasTest, St. Paul, MN, (651) 645-6266, [email protected],
Fittings Unlimited Inc., Dallas, TX (817) 861-2651, [email protected],
Force America, Burnsville, MN, (952) 707-1300, [email protected],
Foster Mfg. Co. Inc., Springfield, MO, (417) 881-6600, [email protected],
Gates Corp., Denver, CO, (303) 744-1911,
Granite Fluid Power, Granite Falls, MN, (320) 564-2311, [email protected],
Hatec International Inc., Houston, TX , (713) 466-6673, [email protected],
Hydraulics Inc., Ft. Worth, TX, (817) 923-1965, [email protected],
Integrated Hydraulics Inc., Mentor, OH, (440) 974-3171, [email protected],
Intertraco (Italia) S.p.A., Suzzara, Italy, +39-0376-539711, [email protected],
John Guest USA Inc., Pine Brook, NJ, (973) 808-5600, [email protected],
Kurt Hydraulics, Lyman, NE, (308) 787-1211, [email protected],
Lenz, Dayton, OH, (937) 277-9364, [email protected],
Manastrip Corp., Rexford, NY, (518) 399-0889, [email protected],
Maxbar Inc., Houston, TX, (713) 263-8712, [email protected],
Nike Hydraulics Inc., McHenry, IL, (815) 385-7777, [email protected],
Parker Hannifin Corp., Energy Products Div., Stafford, TX, (281) 530-5300, [email protected],
Parker Hannifin Corp., Quick Coupling Div., Minneapolis, MN, (763) 544-7781, [email protected],
Pirtek, Rockledge, FL, (321) 504-4422, [email protected],
Powertrack International Inc., Pittsburgh, PA, (412) 787-4444, [email protected],
Pressure Components Inc., Solon, OH, (440) 349-4020, [email protected],
Pressure Connections Corp., Columbus, OH, (614) 863-6930, [email protected],
Prince Mfg. Corp., N. Sioux City, SD, (605) 235-1220, [email protected],
Rectus-TEMA Corp., Randleman, NC, (336) 495-0014, [email protected],
SafeWay Hydraulics Inc., Chaska, MN, (952) 466-6220, [email protected],
Simplex, Broadview, IL, (708) 865-1500, [email protected]
Snap-tite Inc., Quick Disconnect & Valve Div., Union City, PA, (814) 438-3821, [email protected],
Spez-Tech Engineered Fluid Power Technology, Mississauga, ON, (905) 828-5579, [email protected],
Staubli Corp., Connector Div., Duncan, SC, (864) 433-1980, [email protected],
Stucchi Inc, Romeoville, IL, (847) 956-9720, [email protected],
TEMA Fluid Connexions Inc., Pt. Huron, MI, (519) 652-0393, [email protected],
Tomco Products Inc. Painesville Twp., OH, (440) 358-1000,
Yates Industries Inc., St. Clair Shores, (586) 778-7680, [email protected],
ZSI Inc., Canton, MI, (734) 844-0055, [email protected],

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