The modulating valves open automatically when temperature increases at the sensing bulb. No external power source is required to actuate the valve. Not to be used for salt water service. All stock valves are supplied with a drilled and tapped internal by-pass in the regulator body. A solid plug is installed in this hole for 100% shut-off. A drilled orifice plug is packed in an envelope with each valve for field installation, if continuous minimum flow is required. These modulating valves regulate the flow of water to the heat exchanger to maintain a desired exiting oil temperature.