Hydraulic Fittings and Flanges.
Hydraulic Fittings are used to connect pipes, tubes or hydraulic hoses to various components like pumps, cylinders, valves etc. to create a complete leak free hydraulic system and minimal pressure drop. Hence these fittings need to be leak resistant and capable of withstanding high pressures. Various types of fittings allow the Engineers to be creative with their design and help them to change the direction of flow, change elevation lines, split flows and so on in pursuit of the ideal hydraulic system. Fittings include plugs, elbows, unions, tees, cross etc. Obviously, it is very important to identify the correct threads of a connection and use the right match using guidelines from SAE, NFPA and ISO organisations. Hose fittings that work best with a particular type of hoses should be preferred and the manufacturer’s recommendations need to be adhered to . Hoses have a finite life and will eventually fail, hence the need for timely replacement of hose before failure to cut down on expensive downtime.
Connection types are not limited to but include welded connections, threaded (NPT, SAE straight thread, ISO 6149, BSPP, BSPT etc.), barbed, Flanged, quick release, push to connect, 37˚ flare, 24˚ cone, inverted flare, staple lock, face seal, push-fit and others.
Working pressure, type of fitting, vibration, size of piping, desired end connection, flowm material of component, material of conductor, fluid material, fluid temperature, ambient temperature are all important considerations when selecting a type of fitting for the hydraulic system. A general shift to fittings with an elastomeric seal, usually O-rings to prevent leakage can be seen. These fittings include the SAE straight thread, face seal, SAE J518 flanges, ISO 6149 and others. The seal material used must be compatible with the fluid and while leakage is sometime essential for lubrication, unplanned leakage is avoided.
Almost all fittings are made of two components male and female, that are joined together to form a union and are based on the size of the conduit (hose, tube or pipe). The overall dimensions can vary greatly on the type of fitting even for the same size conductor. Again, most fittings are available in different materials like steel, stainless steel, brass, monel, plastic, Teflon (PTFE) etc., for use in different environments that allow for specialisation within a fitting type.
Primarily, the fitting material matches the material of the conductor or component that it is connected to. So stainless steel to stainless steel, plastic to plastic, steel to steel, is the first obvious selection criteria. Fitting geometry is used to identify fitting as per the letters that the fitting diagrams resemble. So you have a Y type fitting, and a T type fitting that are basically run and branch, L type fittings in 37˚, 45˚, or 90˚ elbows to change angle of flows, or swivel fittings that can be at any angle all around, and of course, the straight in-line fittings. Most of these fittings come in a variety of drop lengths (drop length is measured from the centre line of one opening to the centre line of the other). Openings are called ports and sizes of ports though generally same, may vary to compensate for changes in flow. Connection sizes are expressed in sixteenth of an inch. For example a dash 32 size denotes a 2 inch (32/16) connection.
As mentioned earlier, SAE straight threads, O ring face seal and ISO 6149 fittings have an elastomeric seal placed in a groove to seal the fluid. The material of the seal should be compatible with the fluid and the temperature range it is operating at. Elastomeric seals are preferred to reduce the occurrence of a leakage caused by vibration, pressure cycling and thermal cycling. SAE J518 split flange fittings are used on lines sizes ranging from ½” to 2” and above. A flange head with an O ring groove on the face is attached to a conduit (hose, tube, pipe) on one end and secured to the port which typically would be a flat face fitting on a valve, cylinder or a pad on a pump using a 4 bolt clamp either whole or split. The screws or bolts are used to tighten the flange faces to each other to a high torque value to avoid fatigue.
Flared fittings like the 37˚ flare have conical ends called a seat. When this seat is forced against a mating surface by a swivel nut on one fitting engaging with a threaded portion of the mating fitting a ‘seal’ is formed. While the 37˚ flare is the most popular, flared fittings also come in 24˚ and 45˚. These are not interchangeable and are designed to clamp on a tube using a sleeve or a ferrule.
Quick Release or Quick Disconnect couplings allow for multiple reconnections of the connections, some allow disconnection under pressure whereas others don’t, and then some allow pressure from one side of the line to be bled off to remove one source of energy.
Push-to-connect fittings are a one-time connect fitting. These fittings as the name suggests an be pushed on and eliminate the use of wrenches in assembly.
Band and staple fittings are used for low pressure applications. Band fittings have a barbed or beaded end which is pushed into a hose and a band clamp over the hose secures the connection. Staple fittings have a cylinder with a O ring and a bead further up that slides into a socket and the connection is secured by a staple that goes through both sides of the connection behind a bead.
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For a consultation on the right hose and fittings for any of your hydraulic system requirements Contact Inflex Hydraulic and speak to one of our specialists.