There are two types of check valves: straight-through type and right-angle type. The straight-through check valve is installed on the pipeline with a threaded connection. Right-angle check valves are available in three forms: threaded connection, plate connection and flange connection. The hydraulically controlled check valve is also called a locking valve or a pressure maintaining valve. It is the same as the check valve and is used to prevent the reverse flow of oil. However, when the oil flow needs to flow in the opposite direction in the hydraulic circuit, the oil pressure can be controlled to open the one-way valve so that the oil flow can flow in both directions. The hydraulically controlled check valve adopts a cone-shaped valve core, so it has good sealing performance. When the oil circuit is required to be closed, this valve can be used as a one-way lock of the oil circuit to maintain pressure. The hydraulic control check valve controls oil leakage in two ways: internal leakage type and external leakage type. The internal leakage type can be used in oil circuits with no back pressure at the reverse outlet of the oil flow;otherwise, the external leakage type needs to be used to reduce the control oil pressure.