Kwi-30s, ivalve yebhabhathane yaqanjwa eUnited States, yaziswa eJapan ngeminyaka yama-50s, kwaye yayisetyenziswa kakhulu eJapan ngeminyaka yama-60s, kwaye yakhuthazwa eChina emva kweminyaka engama-70. Okwangoku, iivalve zebhabhathane ngaphezulu kwe-DN300 mm emhlabeni ziye zatshintsha ngokuthe ngcembe iivalvu zesango. Xa kuthelekiswa nesango ...
Funda ngokugqithisileyo