Siffofin shigarwa da fitarwa na injin haɓakawa. Akwai madaidaicin juzu'i akan kowane lanƙwasa wanda ya yi daidai da digiri daban-daban a cikin adadi, ana kiransa matsakaicin ƙarfin taimako, wato, wurin da bambancin matsa lamba da ke aiki akan diaphragm na servo ya kai iyakarsa yayin da ƙarfin shigarwa ya karu. Daga wannan lokacin, haɓaka ƙarfin fitarwa yana daidai da haɓaka ƙarfin shigarwa.
Dangane da QC/T307-1999 "Sharuɗɗan Fasaha don Booster Vacuum", ƙimar injin injin lokacin gwajin shine 66.7 ± 1.3kPa (500 ± 10mmHg). Siffofin shigarwa da fitarwa na mai kara kuzari an riga an ƙaddara su ta hanyar hanyar lissafi. Dangane da ka'idar aiki na mai haɓaka injin, ana iya ƙididdige sigogin halaye guda biyu akan madaidaicin halayen: ƙarfin shigarwar da ya dace da matsakaicin ƙarfin wuta da jimla; Matsakaicin ƙarfin fitarwa zuwa ƙarfin shigarwa kafin madaidaicin madaidaicin wutar lantarki, wato rabon wutar lantarki
