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This valve controls the expulsion of oil from the spring side of the second gear band servo piston at speeds in the region of 60 km/h. The time period for oil to exhaust then depends upon the governor pressure varying the effective exhaust port restriction. Line pressure oil from the spring side of the second gear band servo piston passes through a passage leading to the 3–2 kickdown valve annular groove and from there to the 2–3 shift valve annular groove. Here some oil exhausts out from a fixed restriction while the remainder passes via a passage to the 3–2 control valve. As the vehicle speed approaches 60 km/h the governor pressure rises sufficiently to force back the 3–2 control valve piston, thus causing the wasted (reduced diameter) part of the control valve to complete the exhaustion of oil.

Valves control the gas flowing into and out of the engine cylinder. The camshaft and valve spring make up the mechanism that lifts and closes the valves. The valve train determines the performance characteristics of four-stroke-cycle engines.

There are two types of valve, inlet and exhaust. Figure 6.1 shows an exhaust valve. An inlet valve has a similar form. The commonly used poppet valve1 is mushroom-shaped. Figure 6.2 illustrates the parts of the valve. A cotter (not shown in Fig. 6.2) which fixes the valve spring retainer to the valve, is inserted into the cotter groove.Alumina valves and seats

corrosion resistant control valve come in many forms: butterfly valve, ball and seat valve, disk-valve, piston-sleeve metering valve, and dart valve, to name but a few. Alumina has been used in many industrial valves. Water faucet valves of the standard disk-on-disk configuration are very common and are discussed in Section 12.2.8. Since they share almost all the same features of pump rotary valves.

Dart valve plugs and seats are a fluid-flow-control component. When used in the mineral processing industry, or in other industries where slurries, or corrosive liquids, or corrosive slurries are flowing, these valve/plug systems need to be highly wear resistant, especially the plug which can be particularly exposed to the flow of the erosive/corrosive fluids. An example of a dart valve and plug is shown in Fig. 12.17. Alumina valves are an increasingly common technology in general.

One revolution of the camshaft gives the amount of valve lift shown in Fig. 6.3. The valve stem moves in the valve guide and also revolves slowly around the stem. The revolving torque is generated by the expansion and contraction of the valve spring.

An engine basically needs one inlet valve and one exhaust valve per cylinder but most modern engines use four valves per cylinder. This multi-valve configuration raises power output, because the increased inlet area gives a higher volume of gas flow. Contemporary five-valve engines use three inlet valves and two exhaust valves to increase trapping efficiency at medium revolutions.

Figure 6.4 summarizes the functions of the valve. The shape of the neck, from the crown to the valve stem, ensures that the gas runs smoothly. The valve typically receives an acceleration of 2000 m/s2 under high temperatures. Valves must be of light weight to allow the rapid reciprocating motion.

With the single seated control valve lowered, the hydraulic pump is applied to bring the bottom plate of the mould to the lower limit. The separator is then lowered into the mould and fed with the shell and the inner core materials. The vibrator is switched on for 5 s to consolidate the content. The space created by consolidation is topped up. The vibrator is switched on again while the separator is extracted from the moulds. The top of the content of mould is flattened, and the mould lid closed and clamped. With the single seated balanced control valve raised, the hydraulic pump is engaged to stress the content to the desired compaction pressure, which was readable on the gauge. The mould lid is opened and with the control valve raised, the block is ejected from the mould.