Mtundu wa ma valve opangira mankhwala ndi malo ogwiritsira ntchito (ndi mtundu wa mphamvu)
Chemical chomera valavu mtundu ndi ntchito malo (ndi mtundu efficacy) Pambuyo kupangidwa kwa injini nthunzi, m'zaka makumi awiri kapena makumi atatu zapitazi, chifukwa cha kufunikira kwa mafuta, zomera mankhwala, zomera mphamvu, mafakitale zitsulo, zombo, nyukiliya mphamvu ge. ..
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