Robust enough for high-pressure systems, hydraulic couplings are used to connect and disconnect fluid lines. They are designed for high-pressure applications and are used to create tight seals to avoid leaks and spills of water, coolants or other fluids in hydraulic piping systems. Hydraulic couplings come with two ends: male and female. While male couplings come with plugs or nipples, female couplings feature sockets. Most hydraulic couplings are made from stainless steel, carbon steel or brass and are between 1/4 and 2-inches in diameter. As a rule of thumb, the smaller the pipe size the more pressure a hydraulic coupling can withstand.
Hydraulic couplings are often referred to as hydraulic quick couplings or quick release couplings due to the fact they are easy and fast to connect and disconnect without tools. They are typically used with hydraulic cylinders, pumps and manifolds where lines have to be repeatedly connected and disconnected. Some of the industries that utilise hydraulic couplings include construction, agriculture, chemical processing and food processing.
Types of Hydraulic Quick Release Coupling
Hydraulic couplings come in a large range of shapes, sizes and designs. Here are the most popular ones.
Ball lock couplings
The most popular hydraulic quick coupling type on the market, ball lock couplings can be used in a variety of applications. As implied by their name, ball lock couplings feature multiple balls located in holes set along the circumference of the socket body. These holes are stepped so they do not fall into the holes when the hydraulic coupling is not connected. The plug is connected when a spring-loaded sleeve is pushed back to let the balls move outward and then released to force them into the locking cavities. The plug is disconnected when the sleeve is pushed back again, moving the balls outward.
Roller lock couplings
Roller lock hydraulic couplings are equipped with locking rollers positioned in grooves along the circumference of the socket body. When the plug is inserted, the rollers are pushed outward and then slip into a slot on the plug’s outer diameter. The plug is released when the locking sleeve is retracted and the rollers are moved outward.
Pin lock couplings
These hydraulic quick couplings allow one-handed connection since their outer sleeve does not have to retract to enable a connection. As their name indicates, pin lock couplings feature pins positioned around the socket body in a truncated-cone pattern. When a plug is placed in the socket, the pins move back and outward locking it in place. When the sleeve is retracted, the pins are forced to move back and then out of the groove that kept them in place.
Flat-faced hydraulic couplings feature shut-off valves on the male and female parts to greatly minimise any leaks when the coupling is disconnected. They usually limit any leaks to a drop or a film of oil since there is nowhere for fluid to rest. They also prevent air from getting trapped inside the line during coupling. Since flat-faced couplings feature flat surfaces they are also very easy to clean, which can help prevent contamination. Flat-faced couplings can be either threaded or push-to-connect.
Bayonet couplings feature a twist locking system. Upon the insertion of a plug into the socket, a simple quarter-turn twist of the sleeve ensures that it is locked in place. Often used in less demanding situations, bayonet couplings feature lugs on the outside diameter and slots in the socket sleeve. When the plug is inserted into the socket, a quarter-turn twist locks it in position. Twisting the coupling a quarter-turn the other way, on the other hand, disconnects the plug and the socket. Bayonet couplings are more popular in pneumatic than hydraulic applications.
Holmbury couplings and Parker couplings
Holmbury couplings and Parker couplings are the world’s leading suppliers of hydraulic couplings. Holmbury delivers around three million parts to some of the biggest companies in the world annually. Plus, they stock a huge range of products including agricultural couplings, flat-face couplings, quick release couplings, multi-couplings, poppet and ball couplings, pressure washer couplings, rotary couplings and screw-to-connect couplings. Holmbury stocks products made from carbon steel trivalent, carbon steel zinc-nickel, stainless steel and brass.
The largest manufacturer of couplings in the world, Parker features products for the most demanding hydraulic systems. Made from steel, stainless steel, aluminium and brass, Parker’s high-pressure thread-to-connect quick couplings come in a huge range of shapes and sizes. One of the most popular Parker couplings is the FEM series. The non-spill quick release couplings feature a 5000 psi pressure rating and superior corrosion resistance with zinc-nickel plating.
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Hydraulic quick release couplings are usually used in systems where lines need to be repeatedly connected and disconnected. In addition, the more machine productivity increases, the more important hydraulic quick couplings become. One situation where hydraulic quick release couplings are invaluable is on hydraulic testing stands. Meanwhile, pneumatic quick release couplings are often used to rapidly switch between air tools.
Used to cover and protect the connecting surfaces of the coupling plug and socket, dust plugs and caps are often used to extend the lifespan of hydraulic quick couplings. Some of the benefits of these versatile hydraulic coupling accessories include keeping contaminants out of fluid lines and protecting couplings from dirt and grit. Dust plugs and caps can be colour-coded to help identify connecting lines and often come with straps to keep them together when not connected.
There are a few things that need to be taken into account when selecting a hydraulic coupling. These include.
- Is it suitable for the type of material you are working with? Take into account the material’s corrosivity, viscosity, temperature, pressure and flow rate?
- What type of connection and disconnection mechanism do you require? How frequently will the coupling be connected and disconnected?
- What coupling size do you require?
- Will the coupling come into contact with contaminants?
- Does the coupling require shut-off valve/s?
- What material should the coupling be made from (plugs and sockets are often made from stainless steel, steel, aluminium, brass, plastic and plated carbon steel)?
- What is the coupling’s pressure rating? Is it compatible with the operating pressure of the hydraulic system? The hydraulic coupling should have a higher rating than the maximum operating pressure to accommodate any sudden pressure spikes.
Hydraulic fittings are used to connect hoses and pipes to hydraulic cylinders, valves and other components within hydraulic systems. While all hydraulic fittings are used to create a water-tight seal, they can have slightly different functions including moving fluid, changing its direction, or diverting or mixing it. With this in mind, here are the most popular types of fittings.
- NPT, national pipe taper (NPT), fittings come with tapered internal and external diameters and are self-sealing to minimise leaks and spills. This type of fitting is popular in North America.
- BSPT, or British standard pipe taper, fittings are comparable to NPT fittings. They feature one difference, however. Instead of having a 60-degree angle from the crest to the root like NPT fittings, this angle for BSPT fittings stands at 55-degrees.
- SAE, or society of automotive engineers, fittings come with a 90-durometer hydraulic O-ring for superior sealing. SAE fittings are reusable.
- Metric taper fittings are popular in Europe. This type of fitting is often used due to its precise internal and external diameters.