Piston type normally-open blockage-free water drop metering device

The utility model discloses a piston type normally-open blockage-free water drop metering device, and relates to the technical field of water drop metering instruments. The piston type normally-open blockage-free water drop metering device comprises a spring, a piston, a metering bin, a valve opening constant-pressure device and a valve closing constant-pressure device. Water pressure in a water outlet pipeline is quantitatively stored or released in the metering bin, the piston moves, accordingly, a water flowing channel is in a closed state or opened state, and when the water flowing channel is in the opened state, the quantitative water enters a water meter through the quantitative pressure, and the water drop metering is achieved; in addition, when a faucet is in an opened state, the spring is in a natural state, and therefore the service life of the spring can be long; meanwhile, when the pressure of a water inlet pipeline is low, it cannot happen that the piston blocks the water flowing channel through the elasticity of the spring, water stops flowing, and normal water utilizing of a user is affected. Thus, the piston type normally-open blockage-free water drop metering device can meet use conditions and has good application and popularization prospects.