Positioner Sipart PS2 doesn't keep air into actuator

Positioner

Hi,
you have an leakage at the pneumatic system or actuator.
You can check this easily. Just change the positioner to manual mode and move to 50%.
Now the positioner should stay and don't do anything.
In your case I think he will still work or start work after some time.
Also you parameter "DEBA" is set to AUTO.
In this case your deadband will increase automatically up to +/-10% and your jumps will get higher because the positioner will always try to correct the position.

during initialization step 3 you can start a leakage test by pressing "+" button.
It will take one minute and the display will show you how many % of travel range the positioner will move due to air leakage. 0.0 or 0.1 is ok, everything above you should check.

You can use leakage spray or soap water to find the leakage.
Most time at the pneumatic connections or within the actuator.

Positioner

Probably the leakage must be within the actuator or the tubing.
The PS2 is a digital working principal which have nearlyno internal leakage.
It is blocking the output completely, if the valve block would be defect, it would show different behavior.
If you opened the positioner before and remove the inside container, maybe one of the 12 sealing rings get damaged or is not in place.
What you describe sounds like a quite small leakage.
This you will find with leakage spray or liquid.
If you have the chance to block the air into the actuator with solenoid, you could even check the actuator.

 Hi. We checked our actuator by manometer during 24 hours, but air doesn't lose from actuator.

Also we checked Sipart by manometer (picture "Check positioner" in attachment) - pressure decrease always. We checked manometer and fittings by soap water. 

We found leakage in enclosure ventilation by soap water (picture "Leakage.jpg" in attachment.). When positioner set actuator >0%, we see this air bubble. When position is 0.0 %, we have not this air bubble (when actuator have not air). Why does air lose through it? We didn't remove the inside container. We have 3 new Sipart PS2, and we have this problem with all. 

Hi,

This exit are the output of the "enclosure ventilation"
Here very view air will be released if positioner works.
It is purging air which flush the enclosure from inside with a small amount of clean dry instrument air.

The deadband (DEBA) setting will increase and decrease adaptive in "AUTO"
In this case the deviation could be up to +/-10%.
We recommend to use DEBA of 0.2% - 0.3% to keep the deviation small.

The internal positioner leakage is 0,036Nm³/h which is the lowest in marked.
But this you probably see at your application, so the positioner is working from time to time to correct this by venting small amount of air.

Hello,

I'm experiencing the same problem described before on two new valves equipped with sipart sp2. 

It seems that the controller does not block the air to keep the setpoint, it periodically vents some air, causing losing of position, then it moves again the actuator in order to follow the set point.

This behaviour makes me crazy, is there any parameter to set in order to stop these oscillations?

 Just to underline: the oscillation occurs every 1-2 minutes depending on the valve position, moreover when the valve suddenly loses its position I can hear the opening of the piezo inside the Sipart.

Finally, the leakege test says 0.0 and I have noted that if I go in the setting menu when the valve has reached the setpoint the sipart doesn't move the valve!!

Here a video of the behaviour (fixed setpoint of 20%)

Any idea? 

Regards