Principles of Hydraulics by Horst Walter Grollius

Author:Horst Walter Grollius
Language: eng
Format: epub
Publisher: Books on Demand GmbH
Published: 2017-04-14T04:00:00+00:00

KSP1-P2 = 32291bar

As the example shows the calculation of the average compression module must be preceded the definition of a pressure range. The numerical value found for the average compression module is then valid for the specified pressure range.

Solving equation (2.110) for V2 gives

Knowing KS V1 p1 and p2 we are able to calculate the volume V2 at the pressure p2. If, in equation (2.113), the numerical values of the above example used we obtain

2.16 Cavitation

There are two different types of cavitation: the air bubble and the vapor bubble cavitation. Both types of cavitation have similar negative effects on components of hydraulic systems.

Air bubble cavitation: Fluids have the property of absorbing gases in it. One speaks in this connection of the gas absorption capacity of the liquids. Hydraulic oils absorb in particular air. In addition to the dissolved form, the air can also occur in the form of air bubbles in the oil. This happens when local the static pressure of the oil does drop to the gas release pressure (saturation pressure). Then the capacity of the oil for air is exhausted. Pressure reductions of the oil can occur at constrictions of hydraulic components due to increased flow velocities present there (e.g. in valves and hydraulic pumps). Does it come after the constriction due to the expansion of the flow cross-section because of the reduction of the flow velocity to a rise in the pressure then the bubbles will collapse abruptly in form of an implosion.

Vapor bubble cavitation: Is used in technology the term cavitation, so that the vapor bubble cavitation is usually meant. This occurs when vapor bubbles are formed through a reduction in the static pressure up to or below the vapor pressure. Here too the drop in pressure is affected by the increased flow velocities existing at constrictions in hydraulic components. The after the constriction decreasing flow velocity lets the pressure rise again, so that the vapor bubbles (like the bubbles in the air bubble cavitation) will collapse abruptly in form of an implosion.

So cavitation means: Formation of bubbles (air or vapor bubbles) at constrictions in hydraulic components caused by pressure reduction and by the sudden collapse of the bubbles after leaving the constriction by re-increases the pressure. Figure 2.25 is intended to illustrate the occurrence of cavitation in principle in a pipe with constriction.

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