Fig.B-7 Piston transducer for converting hydraulic or pneumatic action
into an action transferred by mechanical motion (and vice versa).
It should be said that and conversion is by no means limited to what is offered by piston-type, hydrostatic transducers - it is also possible to make use of e.g. dynamic action of flowing fluid, as described in chap. [H], or effects of relative flow, chap. [F]. Hydraulic and pneumatic motors or actuators are mainly used for reciprocating motions, which is an area where electric drives have many disadvantages. In Figs. B-8 and B-9 there are examples of typical practical actuator designs. Sealing the piston used to be a problem, but this has been solved both from
Fig.B-8
sealing performance as well as seal life points of view. There is just the inevitable problem of friction force associated with the sealing action, which is particularly unpleasant in systems with low working pressure. A solution may be found in using a diaphragm, e.g. in the form shown in Fig.B-9. Diaphragms
Fig.B-9 A typical example of practical
low-pressure pneumatic linear actuator.

are highly stressed components and this is also a reason why they are limited to low pressure application. In Fig.B-10 there is an example of an application of a diaphragm drive used to transfer not power but information. Of particular importance are combined, multiple conversions - Fig.B-11 shows double conversions acting as an analogy of electric transformers: they can achieve increase of intensity factor (pressure on fluid side, force on the mechanical side) at the expense of the extensity factor




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This is page Nr. B04 from textbook Vaclav TESAR : "BASIC FLUID MECHANICS"
Any comments and suggestions concerning this text may be mailed to the author to his address tesar@fsid.cvut.cz

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