Many fluid systems require that hose be disconnected without excessive fluid loss. For these applications, quick-action couplers are used. They are also used to reduce the time, effort, and skill required to make and break fluid connections. Quick-action couplers are available for hoses from 1/8 to 10 in. diameter. They can typically handle 3,000-psi pressures. Some connectors cannot accept pressures this high; a trade-off is necessary to obtain other important operating characteristics.

Self-sealing couplers can be used in any part of a system where the pressure-drop rating on the coupler is permissible. They are suitable for vacuums down to 10≥ torr. On pump supply lines, a size should be selected that will not produce about 1.5-psi pressure drop at required flow.

A wide variety of seals and materials are available for these couplers: carbon steel, stainless steel, brass, aluminum, many different plastics, bronzes, titanium, and proprietary metals that are inert to most chemicals. Seals are available in Buna N, Neoprene, butyl, VITON®, silicone, PTFE fluorocarbon, and natural rubber, plus many proprietary compounds. Selection of the right materials is simplified by the compatibility charts furnished by most coupler manufacturers.

Many types of couplers are available but all have a few factors in common. Each coupler consists of two halves. Either half may contain a leakproof shutoff valve that closes automatically when the halves are separated, and opens when they are connected. The halves are fitted with a locking device for connecting to each other.

Plain connectors are the simplest and least expensive quick-action coupler. They consist simply of a male nipple and a female coupler, joined usually by a spring-loaded ball-bearing sleeve lock. Typical applications are in laboratory equipment and machine tools, where frequent hydraulic connections are required but spillage is unimportant.

Single-poppet connectors have one plain side and one side automatically closed by a poppet valve. They typically cost about 1.5 times as much as comparably sized and rated plain connectors. In hydraulic circuits they are usually used where lines can be exhausted before disconnection, and as the exit connectors for small portable pumps that spill only a small amount of fluid. Single-poppet connectors are often used in pneumatic circuits, where the poppet closes off the air supply and there is no need to block flow from the actuators.

Double-poppet connectors are the most common type for hydraulic applications. They are typically found on farm equipment, off-road vehicles, and aircraft. The main advantage of the double-poppet connector is that it automatically shuts off flow from both sides of the circuit, allowing only a small volume trapped between the valves to spill when the coupler is disconnected. This feature eliminates the need to drain lines before disconnection, or to provide a means to capture large volumes of spilled oil. However, a double-poppet connector costs about twice as much as a comparable plain connector, has the highest pressure loss of any type, and usually has the lowest pressure rating for a given size. In addition, they are mechanically more complex than plain or single-poppet connectors, and have more potential leakage paths.

Sleeve and poppet couplers have a self-sealing poppet in one half and a tubular valve-and-sleeve arrangement in the other. There is no space for trapped air. When the coupler halves are disconnected, poppet and sleeve are fully closed before the external seal is closed. No fluid is lost upon disconnection; no air is entrained by the fluid upon connection, so freedom from fluid loss and air inclusion is the most important advantage of this type of coupler.

Double rotating ball couplers use a ball in each coupler half. A passageway through the ball is rotated to permit flow. Air trapped between the balls enters the fluid system. This type of coupler causes only a slight pressure drop but is responsible for significant air inclusion on connection and fluid loss on disconnection. Some users report difficulty in sealing when the couplers are disconnected.

Sliding-seal connectors are generally the Cadillacs of the line. When they are opened, the seals are flush with the ends of the coupler and nipple, so spillage is typically less than 0.12 cc -- even for connectors as large as 1 in. diameter. In addition, flush seals leave little space for dirt to collect, and are easily wiped clean. As a result, sliding-seal connectors are almost always used for hazardous or toxic fluids and for other applications where minimum spillage is important. However, these connectors require the highest forces for connection under pressure, and cost about 3.5 times as much as plain connectors.

Stapled coupler is held together with a barbed staple that eliminates the need for wrenches and other assembly tools. The coupler consists of an outer half with openings that accept the staple, and a mating inner half with grooves. Hoses are connected by pushing the coupler halves together and installing the staple so that it passes through the complete assembly. Barbs at the end of the staple lock the coupler. The coupler can be disconnected by squeezing the staple to disengage the barbs.