液压与气压传动Chapter_2 (2).ppt

Example 2-5. Fig. 2-16 shows a sketch of a spool valve. When oil fluid flow through the valve, calculate: the axial effect force of oil fluid on the spool surface. Fig. 2-16 Hydraulic dynamic on the spool valve Example 2-6. Fig. 2-17 shows a sketch of a poppet valve, where the poppet core is 2 . When fluid rate flow q through the valve under the pressure and the fluid flow direction at both statuses of out-flowing Fig. 2-17 a and in- flowing Fig. 2-17 b, calculate: action force magnitude and direction on this poppet core. Fig. 2-17 Hydraulic dynamic on the poppet valve For two cases above the fluid action pressures on the poppet are all equal to F. The action directions are shown in Fig.2-17a and Fig.2-17b respectively. For the Fig. 2-17a the fluid dynamic pressure makes the poppet orifices tend to be closed, and for the Fig.2-17b tend to be opened. So we should be considered according to the detail status and could not consider all tend spool orifice to be closed in any conditions. 2.4.1 States of fluid flow and Reynolds number 2.4.2 Losses along circle parallel pipe 2.4.3 Minor losses in pipe system 2.4 Characteristics of Fluid Flow in Pipeline When a continuity viscous fluid flows through variable section, fluid will lose parts of energy. This can be presented by the pressure loss hw and kinetic correction factor , i.e., in the above mentioned real fluid Bernoulli’s equation here hw includes two parts: pressure losses along parallel pipes and minor (or local) losses. 2.4.1 States of fluid flow and Reynolds number there are three main states of flow, such as laminar, transition and turbulent in a pipe. Now take Fig.2-18 for example. Fig. 2-18. Setup of Reynolds test The experiment proved that, Reynolds number, is consisted of three parameters. The Reynolds number was observed to be a ratio of the inertial force to the viscous force. (2-26) 1 -Overflow pipe 2 -Supply pipe 3,6-Reservoir