Ezimweni eziningi zokusebenza, uma ngokuvamile usebenzisa isitimu, amanzi, noma uketshezi olujwayelekile, ungakhetha ama-valve anezindlela ezimbili ezihlukene zikagesi, eziphathwa ngesandla, nezilawulwa ngomoya.Kodwa-ke, uma uhlangabezana nezinhlayiya ezinezinhlayiya futhi udinga ukuphambukisa neminye imidiya, udinga ukukhetha i-desig emise okwe-V...
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