Can anyone tell me how the DP across the two ports of a 3 way valve affects its controlThis 3 way valve either lets glycerine flow through an exchanger or bypasses it. The dp designed in direction of the exchanger is 0,5bar and towards the byapss its 0,3bar.We are trying to maintain a constant outlet temperature from the exchanger. The valve will divert feed around the exchanger to control this. Presumably there is a constant feed through the other side of the exchanger. The amount diverted will depend on the setpoint of the controller which will regulate within the possible limits of temperature.I can only think that the DP is there for the actuator sizing. The DP across a valve will depend on the flow rate so I'm not sure what basis the DP figures have. These DP figures should not have anything to do with the control as the control is only based on maintaining the temperature.Having said all this my concern is that the flow will always tend to go where there is less DP, so the valve will either fuly close or fully open and not regulate smoothly.Are you talking about a 3way ball valve? If so this type valve is NOT a control device. The valve is designed to change flow direction only. The valve port through the ball is the same a 90 degree elbow in a pipe system. This type valve should be stroked fully i.e. full 90 degree rotation to switch flow direction. This valve is not for modulating service.

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