Drain Valves control the hydraulic flow powering the liftgate up and down movement. Each is composed of two key parts, the valve and the coil. The valve may be 2-way or 4-way, depending on function.
A simple 2-way valve permits oil flow when open, restricts flow when closed. The 4-way controls two different flows through the same tubing, depending on the phase of the procedure. The coil and its hookup control the open and close function.
Key is determining the precise diameter and length of the valve with the accompanying coil to control. Drain valves may also have screens on the valve to help keep lines clear and function at an optimum. Clogged drain valves can quickly hamper liftgate performance.