Hello everyone!
I hope that you're all doing well

Currently, I'm working on my project that controls the pressure in a closed system. I'm using Arduino mega controller connected to a pressure transducer and a vacuum pump. The vacuum pump should turn ON when the pressure in the system is above 50 kPa, and once the pressure be below that point the pump should turn OFF and the pressure in the system should remain at that level.

However, when the pressure in the system is < 50 kPa the vacuum pump is turned OFF and within seconds it goes above 50 kPa and then turns ON and then OFF... and so on. The vacuum pump keeps turning ON and OFF at that point (50 kPa). I realized later that the vacuum pump isn't isolated from the atmospheric pressure, in other words once it OFF the pressure in the system goes back to the atmospheric pressure (101.325 kPa) because the other end (vacuum pump) is open to the atmosphere.

So, now I'm looking for a device or switch that can be connected between the vacuum pump and the closed system so that when the vacuum pump if turned OFF the pressure in the closed system remains at that level without raising back to the atmospheric pressure.
PLEASE SEE THE FIGURE BELOW FOR CLEAR ILLUSTRATION

I hope you got what I meant, and looking forward for your ideas and suggestions
Regards,

 

A simple vacuum check valve should work at those vacuum levels.

 

MAP sensor - Wikipedia
You can get a General Motors manifold absolute pressure sensor(MAP sensor) for next to nothing at an auto salvage yard. They put out a variable voltage that you can read with an ADC.

 

When working with a vacuum system you cannot have any leaks, even a small leak. Next, you want some hysterisis in your pump control loop. You would include this in your Arduino code. For example when your vacuum pump pulls down to 50kPa the pump turns off but when it turns off you are getting some back leakage and once your pump turns off it will turn back on. You need to add hysteresis to your threshold value making threshold value(s). Pump down to 50 kPa and give yourself a window where your pump will not turn on again until your closed system gets up to maybe 51 kPa. Again, I can't stress the importance of using good quality vacuum line fittings and plumbing. A good vacuum system will not leak. Google Arduino Hysteresis Code Sample and you should get some code samples using hysteresis.

Lastly, if what you are saying is when the pump turns off the vacuum line on the pump returns to atmos then as suggested try a check valve. However, if not already done I suggest the Arduino code be modified as suggested.

Further thought I have worked with several systems which used a solenoid valve on the Vacuum Out. Pump on valve open, pump off, valve closed.

Ron

 

check valve.

https://www.grainger.com/product/CD...m/rp/s/is/image/Grainger/6D914_AS01?$smthumb$