The oil tank is obviously an essential element in an electro-hydraulic power unit. It can be made of metal or white or black plastic. In some cases, the ECU cassettes also perform the function of a tank. In most cases, however, the tanks are made of plastic material because they are made with the most particular shapes, having to adapt to the confined and contained spaces available. Some tanks are tub-shaped, so open at the top; others are long and square or round in cross-section, because they are housed inside the main frame of the tail lift.