ZDT series automatic circulating pump protection valve is a kind of pump protection device. It automatically protects centrifugal pumps, especially hot water media, from partial cavitation damage and instability that may occur in the pump body during low-load operation. Once the pump flow is below the preset flow, the bypass is fully open to ensure the minimum flow required by the pump. Even if the main circuit is completely closed, i.e. the main traffic is zero, the minimum flow can be automatically cycled by bypass. The pressure is reduced by an integrated multi-stage throttle regulator in the bypass. The ZDT series has a larger caliber bypass. This valve is used for large bypass flows with differential pressure up to 4MPa, the choice is determined by the factory.