JOHN GUEST 12mm In-Line Shutoff Valve. John Guest Push Fit Connectors. The speedfit system of fittings and pipe is designed for hot or cold water systems in touring caravans. The pipe is simply pushed into the fitting to form a safe secure connection. The body is produced in acetal copolymer. ‘O’Rings are nitrile rubber. The collet is produced in acetal copolymer with stainless steel teeth. Minimum Working Temperature -20°C. Maximum Working Temperature +70°C.