Fig.G-28
Fig.G-30





















By the reverse combination it is possible to perform amplification of mechanical motions - through hydraulic or pneumatic intermediate action. This is the principle of servomechanisms - Fig.G-28. Note the influence of the mechanical feedback. In a servomechanism, the feedback acts as a negative, stabilising one. On the other hand, a positive feedback may keep the system in permanent oscillations. This is the foundation upon which the principle of piston engines (beginning with steam engines) is based.



- It is assumed that the pumps or blowers in the present studied circuits are not of the positive displacement type, but they are of the turbomachine sort - either the radial (centrifugal) ones discussed in chapt. [F], or axial (or perhaps diagonal) ones. As was shown in connection with Figs.G-15, G-16, it may be assumed that at least in the vicinity of the operating point the characteristic of the machine may be described by the quadratic dependence Fig.G-15. When the pump or blower is connected together with some load
Fig.G-31
the equation of the characteristics, that of a load as well as that of the load, must be obeyed simultaneously. This is the condition enabling us to evaluate the flow and energetic drop in the circuit. Graphically, the condition of simultaneous fulfilment means that what we are looking for is the intersection point of both characteristic curves. This is shown in Fig.G-31. The dissipance of the source (= pump) is denoted in Fig.G-31 as while that of the load is . It is apparent that the problem is equivalent to solution of a circuit consisting of two restrictors in series (Fig.G-19) suppled from an ideal source of = const.


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This is page Nr. G09 from textbook Vaclav TESAR : "BASIC FLUID MECHANICS"
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