RC Spool Hydraulic Directional Valve 8Mpa With 4mm Connector For 1/12 1/14 1/16 Hydraulic System Model. The valve block supports self-upgrade for. For example, if you have a 3-channel valve block, you can upgrade it to. 4 to 8 channels. Please refer to the tutorial video above; the entire upgrade process is very simple and easy to operate. Processing technology: CNC super-finishing. Product medium: 46# hydraulic oil. Product features: supports future upgrade for more channels, delicate operation, small size, beautiful appearance, etc. Note:Without central oil return function, you can use it with the overflow valve from our store. When the cylinder reaches the longest and shortest stroke, the overflow valve automatically opens the pressure relief valve to drain the oil into tank.