How air is getting into your pressurized hydraulic system?

Air typically enters the hydraulic system through the the pump inlet and, under certain conditions, past the rod seal of a double-acting cylinder.
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But air can also invade the system through joints in pressurized plumbing.
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When fluid travels through a pipe or hose at relatively high velocity – in a pressure line for example, and has to change direction through a tee or elbow, a venturi effect can be created.
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Because the sealing arrangement of the hydraulic connector is designed to withstand positive pressure – but not negative pressure, air can be drawn into the system – even when the plumbing has no apparent leaks.
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If you made a glass model of a pipe elbow and connected a measuring point in the middle of the angle, you would see a negative pressure when fluid passed through the elbow at high velocity.
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And if you looked carefully, you’d likely see air bubbles entering the system through the seal of the measuring connection.
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What it comes down to is use as few sharp angles – tee-pieces, elbows, etc in hydraulic plumbing as possible. a

Craig Cook