... the temperature difference circulation pipeline. When the temperature difference between solar collector outlet and storage tank arrives at the setting figure ... material: copper 4) Water capacity: 150L, 200L,300L, 450L,5) Pressure: 0.6MPa6) Heat preservation: 78h7) Hail resistance of vacuum tube ... ,30,36,45tubes with 58mm diameter and 1.8m length solar water heater (split design, bear the pressure)