{"id":2788,"date":"2024-03-07T14:43:39","date_gmt":"2024-03-07T13:43:39","guid":{"rendered":"https:\/\/www.bf-hydraulik.com\/encyclopedia\/drain-line\/"},"modified":"2026-04-15T11:52:51","modified_gmt":"2026-04-15T09:52:51","slug":"drain-line","status":"publish","type":"encyclopedia","link":"https:\/\/www.bf-hydraulik.com\/en\/drain-line\/","title":{"rendered":"Drain line"},"content":{"rendered":"\t\t
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Drain line<\/h1>

The drain line<\/a> is a safety measure for pumps, radial motors, and cylinders in hydraulic systems<\/a>. It serves to keep the pressure within the housings of these components constant. <\/p>

Necessity of the drain line<\/h2>

Highly loaded hydraulic components are technically very difficult to seal. Internal leakage<\/a>s occur in many areas. This oil collects in the housing and must be discharged. If it is not, the internal pressure will burst the seals and the housing. For this reason, openings are provided on the components through which the leakage oil can escape. The line that carries away the leakage oil is called the drain line<\/a>. <\/p>

The paths of the leakage oil<\/h3>

Leakage oil does not differ in any way from hydraulic oil. It is part of the normal fluid that is initially lost through leakage. For this reason, leakage oil must be included in the calculation of volumetric losses. These leakages, for example at piston rings or non-sealable components such as pump gears, are technically unavoidable. The oil exits through the holes provided for this purpose and initially runs through the drain line<\/a> through a leakage oil filter. This is required to filter out dirt particles and abrasion from the hydraulic oil. <\/p>

Since the leakage oil flows past narrow gaps under high pressure, it has a strongly abrasive effect on its surroundings. These particles of rubber, bronze, or carbon can be very destructive and can also remain unnoticed for a long time. Therefore, a drain line<\/a> always includes a corresponding filter. From the leakage oil filter, the oil flows back into the hydraulic tank<\/a> via another drain line<\/a>. There it mixes again with the normal hydraulic oil. The circuit is closed. <\/p>

Different methods for calculating the drain line<\/h3>

Calculating the drain line<\/a> is complex. A distinction is made between three applications: <\/p>