Method for monitoring the change in state of a valve by measuring pressure

1. A method for monitoring a change in state of a valve in a turbo-engine start up circuit following a command to change the state of said valve comprising:

measuring a first value of ambient air pressure under a fan cowl of the turbo-engine a first time after said change state command is issued and before said valve receives said change state command;

measuring a second value of ambient air pressure under the fan cowl at a second time after said valve receives said change state command;

comparing the first value of the ambient air pressure under the fan cowl measured at said first time with the second value of the ambient air pressure under the fan cowl measured at said second time; and

determining whether or not the valve has actually changed state based on a difference between the first value of the ambient air pressure under the fan cowl and the second value of the ambient air pressure under the fan cowl,

wherein the valve is determined to have actually changed state when the difference is greater than or equal to a predetermined threshold value.

2. The method according to claim 1 , wherein said determining includes determining that the valve is open after said change valve state command when the second value of ambient air pressure under the fan cowl is greater than the first value of ambient air pressure under the fan cowl.

3. The method according to claim 1 , wherein said determining includes determining that the valve is closed following said change valve state command when the second value of ambient air pressure under the fan cowl is less than the first value of ambient air pressure under the fan cowl.

4. The method according to claim 1 , wherein said determining includes calculating an air pressure gradient under the fan cowl when said change valve state command is given.

5. The method according to claim 4 , wherein said determining includes determining that the valve has changed state when an absolute value of said air pressure gradient is greater than a predetermined air pressure gradient threshold value.

6. The method according to claim 1 , wherein the start up circuit comprises first and second position sensors to determine if the valve is open or closed, and wherein said measuring, comparing, and determining are performed when an information about the state of valve output by the first position sensor is different from an information output by the second position sensor.

7. The method according to claim 6 , further comprising determining which of the first and second position sensors is defective.

8. An aircraft turbo-engine comprising:

a start up circuit, said start up circuit comprising a pneumatic starter and a starter pressurized air supply valve;

means for measuring a first value of ambient air pressure under a fan cowl of the turbo-engine at a first time after a change state command of the pressurized air supply valve is issued and before the pressurized air supply valve receives the change state command;

means for measuring a second value of ambient air pressure under the fan cowl at a second time after the pressurized air supply valve receives said change state command;

means for comparing the first value of the ambient air pressure under the fan cowl measured at the first time with the second value of the ambient air pressure measured at the second time; and

means for determining whether or not the valve has actually changed state based on a difference between the first value of the ambient air pressure under the fan cowl and the second value of the ambient air pressure under the fan cowl,

wherein the means for determining determines that the valve to have actually changed state when the difference is greater than or equal to a predetermined threshold value.

9. A method for monitoring a change in state of a valve in a turbo-engine start up circuit following a command to change the state of said valve comprising:

measuring a first value of ambient air pressure under a fan cowl of the turbo-engine before said change state command at a first time;

measuring a second value of ambient air pressure under the fan cowl after said change state command at a second time;

comparing the first value of the ambient air pressure under the fan cowl measured before the change state command with the second value of the ambient air pressure under the fan cowl measured after the change state command; and

determining whether or not the valve has actually changed state based on a difference between the first value of the ambient air pressure under the fan cowl and the second value of the ambient air pressure under the fan cowl,

wherein the valve is determined to have actually changed state when the difference is greater than or equal to a predetermined threshold value, and

wherein the start up circuit comprises first and second position sensors to determine if the valve is open or closed, and wherein said measuring, comparing, and determining are performed when an information about the state of valve output by the first position sensor is different from an information output by the second position sensor.