Pressure relief valve

[huberdoo]

I have a Pentair cartridge filter that has a valve on top of the housing. It has a warnibg label that the valve
must be fully open when starting pump to prevent the housing to blow off if too much pressure. I opened it fully
but when the pump is started water spews out the valve.
Please help a true novice with some advice. Thanks much.

[Poconos]

Hi and welcome to the forum. Still not sure who can see this forum so I'll take a shot. I've never dealt with cartridge filters but I suspect that valve is an air bleed valve. I think you should open it until water comes out then close it. This assures a full charge of water in the housing. As for the comment about blowing it apart, no. The pressure is not determined by how much air is in the system but by the pump, flow restrictions etc. The danger is if you have a large volume of air under some pressure, and for some reason the tank lets go you will have a pretty violent explosion and this is because the air is compressed and will expand when released. If you have a full charge of liquid, which is incompressable for all practical purposes, if the tank blows there won't be an explosive event. The water will just be released.
Hope this helps.
Al
PS: If I'm wrong with my thinking, someone please correct me.

[madwil]

sounds right- that's how the cheapo cartridge filters from Intex work, at least...

[Poconos]

I would think the presence or absence of a valve wouldn't have anything to do with the quality of the filter but rather the design. If there is no way to automatically get the air out then you need a manual method. I'm suspecting it is intentional in that the Hayward sand filter I have has a little extra clearance between the center pipe and the mating outlet pipe to bleed any air out.
Al