Quick couplers are quick-disconnect fittings used in a hydraulic or pneumatic system to quickly connect lines without losing fluid or fluid pressure. Quick couplers are designed to be connected and disconnected immediately without the use of tools, eliminating the need to close valves, bleed the system, recharge with fluid, and/or purge entrapped gas when parts are disconnected and replaced. For this reason, they are especially useful in critical or time-dependent production applications where speed is key. Quick couplers also save valuable time when used to construct or tear down plumbing systems.

Connection Types

When selecting quick couplers, the buyer must consider the connection types of both the quick coupler end and the ends connecting to the rest of the system.

Quick Coupler Connections

There are a few types of fast connections that fall under the domain of quick couplers.

Ball and sleeve connections employ a "ball" or male end which fits into a female outer sleeve. The sleeve can be pulled back by the user for retraction in order to connect and disconnect the halves of the coupler.

Cam-lock fittings are connected using tabs on the female half which fold down to lock the receiver in place after it is inserted. These fittings allow for quick, secure connections of hoses to tanks or other hoses. They are used in many heavy-duty hose applications such as fire hose and sludge/sewage pumping.

Luer locks are sleeve fittings that afford simple, effective connections via a quick twisting action. They are generally made for short, single usage. They are most commonly used in medical and laboratory applications.

Push-to-connect fittings have ends that are made to connect by simply pushing one end into another. They work similarly to (and are sometimes synonymous with) ball and sleeve connections. They use a simple collar retraction method for disconnect.

This video details push-to-connect fittings.

Image credit: Tifco Industries Inc. / CC BY-SA 4.0

Twist or bayonet fittings incorporate a twist motion (1/8 - 1/4 of a turn) that engages and disengages the connection.

System Connections

When selecting quick couplers, another important distinction is what the other end of each piece of the quick coupler connects to. There are an assortment of different connection types available for attachment to a variety of systems and vessel types.

Compression fittings are fittings which connect tubes using compression on a gasket, ring, or ferrule. The compression typically is made by tightening a nut onto the connection threading over the tubing and ferrule. Quick coupler ends made for compression connections have open female threads with cavities designed to accept ferrules or compression rings.

In specific applications, quick couplings may be required to connect to a flange at one end of the adapter. Flange fittings are rims, edges, ribs, or collars with flush surfaces.

Plain end connections are used to allow connectors to be welded, brazed, soldered, or glued to the associated pipe or tube.

Threads are the most common connections used for pipe, tube, and hose fittings, and thus are standard for most quick coupler adapters. Each half of the quick coupler typically contains a separate gender of thread.

Sizing

Quick coupler sizing is determined by the pipe, tube, or hose diameter that the adapter connects to. For example, a 1/2" quick coupler is designed to connect to a pipe with a nominal size of 1/2 inch. Diameter sizes are measured in millimeters (mm) according to the Metric system or inches (") according to the U.S. customary system.

Materials

The materials for quick couplers are typically selected based on the fluids being transported through the system. Other selection factors include cost, flexibility, environmental conditions, and required pressure ratings. Material choices include different types of plastic or metal.

Common metals include:

Aluminum - lightweight and corrosion resistant. Aluminum is commonly used for plumbing and is the preferred fitting material for aluminum tubing. By itself, aluminum has low tensile strength and is used when high corrosion resistance is needed. It is alloyed with zinc, copper, silicon, manganese, and/or other metals to improve its strength and hardness.

Brass - strong, durable, and corrosion resistant, with high temperature ductility and good conductivity. Brass is an alloy of copper and zinc, and is a commonly used quick coupler material because of its machinability and its excellent performance properties. Brass fittings can have various protective or decorative finishes which should match the finish of the tubing.

Cast iron - strong and highly abrasion resistant. Cast iron fittings and tubes are used primarily in building construction for sanitary, storm drain, waste, and vent tubing applications because of their resistance to abrasive materials like sand, gravel, solid wastes, and debris.

Copper- extremely corrosion resistant with excellent conductivity. Copper fittings are important for many plumbing and heating applications, and are commonly used for residential water supply lines. Copper fittings are usually used in conjunction with copper tubing, and come in either soft or rigid forms. Soft or ductile copper is easily bent and maneuvered, and is the only type suitable for flare connections. Rigid copper is not bendable and requires directional fittings to go around corners and obstacles.

Steel - durable and strong, with a high resistance to heat. Steel is an alloy of iron and carbon - it is commonly alloyed with other metals to improve its corrosion resistance and durability. It is used in both commercial and industrial applications for carrying water, flammable gases, and other fluids. Galvanized steel is coated with zinc for rust and chemical corrosion resistance. Carbon steel is alloyed with higher levels of carbon for increased durability and strength.

Stainless steel- relatively strong with excellent chemical and corrosion resistance. Stainless steel is an alloy of steel that contains over 10.5% chromium, providing excellent corrosion resistance for sanitary applications and those dealing with aggressive fluids and materials. It is a common choice of material for quick couplers.

Common plastics include:

Fluororesins (PFA/PTFE/PVDF) - plastic resins that contain fluorine. They are used for high temperature applications up to 500°F (250°C). These materials exhibit very good chemical resistance and dielectric properties.

PVC (poly-vinyl-chloride) - a rigid plastic which can come in a variety of pressure ratings. PVC couplers are connected to via threads or solvent welding (glue). Standard applications include cold water supply and drainage.

Polyethylene (PE) - a soft, flexible, and tough thermoplastic - even at low temperatures. PE couplers offer outstanding electrical properties, but poor temperature resistance. They also have very good chemical resistance, but are prone to environmental stress cracking; they have poor UV resistance (unless modified) and poor barrier properties, except to water.

Polypropylene (PP) - thermoplastic material that exhibits excellent cold flow, bi-axial strength, and yield elongation properties. It is similar to PVC, but can be used in exposed applications because of its resistance to UV, weathering, and ozone.

Application

Quick couplers may be specifically designed and rated for a particular application or industry.

• Chemical fitting - Chemical quick couplers may be designed for specific chemicals such as fuel, oil, solvents, acids, bases, etc.
• Gas fitting - Gas quick couplers are specifically designed for explosive and noxious gases such as propane and phosgene.
• Hydraulic fitting - Hydraulic quick couplers are designed and rated specifically for hydraulic lines. Of particular importance for these quick couplers are high pressure ratings.
• Pneumatic fitting - Pneumatic quick couplers are specifically designed for use in compressed air lines and pneumatic systems.
• Sanitary / food-grade fitting - Sanitary and food-grade quick couplers are designed and constructed for use in sanitary applications such as the food, beverage, medical, and pharmaceutical industries.
• Water fitting - Water quick couplers are rated for use with potable water, typically pressurized, for industrial, municipal, and consumer use.

Standards

ISO DIS 13031 — Earth-moving machinery — quick couplers — safety

BS ISO 5675 — Agricultural tractors and machinery — general purpose quick-action hydraulic couplers

References

Quick Couplers — Parker Hannifin

Image Credits:

Hangzhou Mingfeng Manufacturing | Snap-Tite