The Manual On-Off control is used to open or close the valve. The flow through the valve is controlled by a rubber sleeve which is actuated by hydraulic pressure. The valve is either in the fully opened or the closed (shut off) position. The “Auto” position on the selector has no effect on valve control but is used when the valve is equipped with automatic controls. The manual selector can be used to hold the valve partly open by opening the valve part way and then pointing the selector handle midway between “Open” and “Close”.