Compressed-gas type quantitative water-saving draining valve

A pressed water drain valve which discharges water by quantities can be used to improve the old-type water closet with one-time-fixed-quantity drainage into a water-saving water closet with large drainage amount and small drainage amount. An exit hole is notched under a sealing face of a rubber water drain valve. According to the principle of water pressing air, that is making use of the water pressure to discharge the air in the water drain valve and then cooperating with the plastic water inlet which is provided under the water drain valve to adjust the air discharging amount in order to control the close time of the water drain water. Thus the water drain valve can be used to form large amount, small amount and any amount of draining water. All the old water closet can be improved into a water-saving water closet.