https://www.zfzl.com/product/vacuum-pumps-refrigeration-tools-1/vacuum-pump-accessories/ A pump cannot compensate indefinitely for a restricted evacuation path. Small-diameter hoses, long connections, restrictive manifolds, service valves, and valve cores can reduce conductance between the refrigeration system and the pump. Recent field guidance recommends using short, large-diameter, vacuum-rated connections and minimizing unnecessary restrictions. This is particularly important when technicians are trying to evacuate larger systems or diagnose why pressure stops falling as expected.