Flow Through Valves

Most hydraulic servomechanisms or other high-performance systems rely for their operation on the metering of fluid through a valve. This chapter deals with a linearised method of analysis for ‘four-way’ valves. They are called this because they have four connections, one for the supply pressure, another for the exhaust, plus two control ports through both of which fluid may be metered, either from the supply to the system or from the system to the exhaust. (A valve may have five ports but these include either two pressure ports or two exhaust ports which can be connected together.) Such valves may be of the spool type as sketched in figure 7.1 or of the nozzle-flapper types. Other sorts of valves are used and the theory in this chapter is extended in appendix B to cover ‘three-way’ valves whilst a little information about poppet valves is given in appendix C.