The Sun DTDANHS is a high-performance, pilot-to-open check valve with a pilot-assist feature, commonly utilized as a counterbalance or load-holding valve. It permits free flow from the directional valve (port 2) to the load (port 1) while blocking flow in the reverse direction. Flow is allowed from port 1 to port 2 only when pilot pressure is applied at port 3. The pilot-assist function provides smooth, stable operation by helping the valve to open and close, making it ideal for controlling overrunning loads and preventing cavitation in demanding hydraulic applications.