Traditional Culture Encyclopedia - Hotel franchise - What does it mean that the allowable leakage rate of gate valve is class D?

What does it mean that the allowable leakage rate of gate valve is class D?

In GB/T 13927, the leakage rate of valves is divided into 10 grades, namely A, AA, B, C, CC, D, E, EE, F and G grades. It is also stipulated that when there are no special provisions in the order contract, the metal sealed valve should meet the requirements of class D.