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Leak testing the control bottle with positive pressure

Hi.
I am going to do a positive pressure test in the control bottle by applying positive pressure into it to look for leaks. How many bar is maximum recommended into the enclousure?

Hi @Jhans,

I don’t expect we have hard numbers on this, as our current enclosures are designed only for negative pressure and don’t have a positive pressure rating. I’ve asked our design engineers if they have an indicative number where the end-caps may push out, and will get back to you with the response :slight_smile:

If it’s helpful, previous mentions of “positive pressure” have specified “a bit” or “a slight positive pressure”, and the only quantitative results I could find (from a community member) said

The following comment may also be useful to avoid the vacuum plug coming out when positive pressure is applied:

@EliotBR I made these brackets to hold keep the lid in place when i apply positive pressure.
I applied about 2,5 bar pressure into the enclousure.
The result was that the camera dome cracked at a around 2,5 bar. Maybe it had a small damage from before, i don’t know. But im not putting any more pressure than 2 bars from now on…

The end caps push out when you reach above 1 bar, since that is the athmospheric pressure that is holding it in place.

Following up on this,

Your cracked dome can perhaps serve as a timely/convenient example of why it’s not recommended, and why it can be dangerous - internal positive pressure pushes the enclosure outwards, so if something breaks off it can be propelled towards nearby equipment.

It’s also worth noting that the dome is attached via screws, which normally push the dome base onto an o-ring and the large flat surface of the flange. Normal operation (external pressure) pushes it more onto that face, and the resulting stress is evenly distributed. By reversing the pressure direction to positive internally, the dome instead pushes outwards towards the mounting screws. That changes the normal widely distributed low-pressure push into a force over the much smaller screw head areas, resulting in stress concentrations at those locations and a much higher likelihood of issues like cracking/fractures.

While it’s true that the caps are being pushed outwards as soon as the internal pressure is larger than the external atmospheric pressure, the end-caps will have some amount of friction holding them in place, and the amount would depend on the manufactured part tolerances, along with the o-rings, lubrication, and a number of other factors.

We did a test with putting only a slight positive pressure with an compressor gun through the vent port and it resulted in an sudden breach of the acrylic dome. The dome exploded into tiny bits and pieces all over the workshop. Luckily noone got hurt, so I would at no point do that again :slightly_smiling_face: