A gate valve is designed for use with water in low pressure systems where the pressures involved are only a few metres head (less than 1 bar). They are used to temporarily turn off supplies for maintenance. When the valve is open, the gate gets fully drawn up into the valve, which leaves an opening that is about the same size as the pipe installed in the valve. This allows water to freely flow, since there is little restriction in the valve. When the valve is closed the gate is down - though often the seal is not completely perfect.