Hydraulic breather caps are parts used to protect equipment against moisture and particle contamination. Moisture vapour is stripped from the air and expelled back into the atmosphere by pump cycles which means moisture is exerted with each flow cycle by the opening and closing of the breather caps. These caps also prevent dirt particles from entering the equipment at very high efficiency rates.What are hydraulic breather caps used for?Air trapped within hydraulic systems expands significantly above 72°C. This can cause vibration and unsteady function of machinery. Hydraulic breather caps release the trapped air to bring the system back into balance. Breather caps are often used in oil-cooled electrical transformers. They can also make up venting parts for gearboxes.Mobile equipment (such as petrol tankers) has breather caps fitted to prevent explosions due to the motion of combustible materials in transit. Types of hydraulic breather capsSome hydraulic breather caps have added valves (double or vacuum) and others come with dipstick options. These caps can also have attached sealing discs that prevent hydraulic fluid leakage and keep dust particles out. Breather caps come in threaded, screw-on or bayonet configurations.