Pressure vessel under negative Pressure

[Paul Arthur]

Hi Guys,
I often use large composite GRP pressure vessels in my water treatment designs and typically they are designed by the manufacturer for a test pressure of 350kPa.
Typically, they would operate at pressures below 120kPa.-
See attached.
Every so often, the water in the top vessel connection goes into negative pressure, typically no more than -30kPa.
The manufacturer says the vessels should never come under negative pressure, but I know that rubbish as they couldn't operate in my water treatment plants if that were true.
My question is, what should I know about this so that I can be better informed when discussing this with the manufacturer.
Thanks
Paul

 

[r6155]

What is the CODE?
Experience in design, manufacturing, and inspection is required to be able to discuss with the manufacturer.

 

[akpipelineengr]

Composites don't do great in compression. Just because it hasn't failed yet, doesn't mean you aren't accumulating damage.

Titan_submersible_implosion

 

[jt1234]

If you have negative pressure on the top, that means somewhere in the top or the pipe line got plugged or stuck while you are draining the water out from the lower section. Check the piping system connecting to the top head to see where is the bottleneck or any valve unnecessarily closed during operation.

 

[SnTMan]

Might consider an air admittance valve...

Regards

Mike

 

[Snickster]

The top of the vessel is the downstream side of the filter elements. If you are getting a negative pressure sometime then it appears at these times you are getting an abnormally high pressure drop across the filter. This could be due to clogging up the filter which indicates possibly the need to regenerate the filter more often. So basically the filter is becoming caked up with the filtered particles and need to be backwashed more often.

Ask the vendor what they think may be causing the pressure drop across the filter to be abnormally high.

Do you have a schematic of your system? Something don't make sense because would not the discharge ig such system be to an atmospheric vessel such as a swimming pool where in this case pressure on downstream of filter will approx atmospheric always?