If a pneumatic mixing valve has a tear in the air side diaphragm, what will happen to the position of the mixing valve?

When there is a tear in the air side diaphragm of a pneumatic mixing valve, it negatively impacts the ability of the valve to respond correctly to control signals. The diaphragm is crucial for translating pressure signals into mechanical movement; if it is compromised, the valve's ability to hold or adjust its position becomes erratic.

With a tear in the diaphragm, the pressure that is needed to control the valve position can be lost or become unstable. Typically, this would mean that air pressure from the control mechanism might not be effectively pushing against the other side of the diaphragm, leading the valve to move towards the default position.

In many cases, this default or failed position is fully open because that is often the result when there is insufficient control pressure to maintain a closed position. Therefore, as air pressure is not counterbalanced effectively on the diaphragm, this results in the valve inadvertently moving to the open position.

Thus, the correct answer is that the valve will open as it fails to maintain a controlled position due to the damage to the diaphragm.