Hydraulic Screw-in Fittings

Screw-in fittings are small but important components in hydraulic systems. They ensure the permanent and secure combination of various assemblies, units, and lines. With the help of screw-in fittings, hydraulic systems can also be expanded as desired.

Function of Screw-in Fittings in Hydraulics

Screw-in fittings enable the almost arbitrary combination of hydraulic components. This allows designers to always react flexibly to any requirement for a hydraulic system – including the cost factor. Screw-in fittings are manufactured in many variants:

• Adapters
• Elbows
• T-pieces
• Straight Connectors
• Connectors for Fine and Metric Threads
• Rigid Connectors
• Screw Connectors with Loose Internal Thread
• … and much more.

Each type of screw-in fitting is equipped with a standardized diameter and commercially available thread. This ensures the seamless combination of all components in a hydraulic system.

Requirements for Screw-in Fittings

Screw-in fittings are manufactured with varying complexity. The simplest components of this type are straight connectors with two external threads. The next stages of development are branches, T-pieces, or adapters for different diameters or thread types. Screw-in fittings with loose internal threads allow another component with an external thread to be screwed on.

Regardless of how a screw-in fitting is manufactured, it must meet the following conditions:

• Highest quality
• Pressure resistance according to the application
• Corrosion-resistant
• Temperature and acid resistant

This high manufacturing quality is necessary to combine the screw-in fittings with any components. Installers must be able to rely on the threads always fitting and the diameters corresponding to standard inch dimensions. Only then can complex hydraulic systems be assembled at all.

Since hydraulic systems often operate under very high internal pressures, the screw-in fitting must be designed accordingly. For high-performance systems, such as those in construction vehicles with internal pressures exceeding 400 bar, only screw-in fittings made of high-strength steel are suitable. Fittings made of aluminum or plastic would pose too great a risk here.

High-strength steel, however, always comes with a major drawback: it rusts. A screw-in fitting must therefore be protected against both external and internal corrosion. This is usually achieved by a zinc coating. However, not only the fittings but also the sealing elements must meet the chemical and heat-related challenges of a hydraulic system. Therefore, a designer should always study the data sheet of the sealing material used to make the correct selection.

Application of Screw-in Fittings in Hydraulics

Screw-in fittings can conveniently combine fixed or flexible hydraulic lines with hydraulic components. These include:

• Lines and Hoses
• Fittings
• Hydraulic Motors
• Pumps
• Tanks
• Piston and Bladder Accumulators

It should be noted, however, that even high-quality screw-in fittings are a weakening of the system! Due to permanent pressure, cavitation, and particles in the lines, the seals in these connecting elements suffer particularly. The fewer seals there are in a hydraulic system, the safer it becomes. It is therefore advisable to use screw-in fittings only where no other solution is available.

Furthermore, every hydraulic system requires a powerful filter unit and measures against the formation of cavitation. Thus secured, the lifespan of all seals and components is significantly increased.

Screw-in fittings can always be easily repaired by replacing the seal. If the technical parameters of the seal are known, failure can be prevented by interval-based, preventive replacement of the seals.