How to fix this pressure toilet

From the best plumber Vancouver WA 98682

My toilet has this pressure vessel device The valve stays open and it doesnt fill up and keeps draining, If i pull up on the valve it closes but after a few flushes it stays open again Anyone know how to fix this? Thanks Attached image , the valve is right in the center like a cylinder

https://imgur.com/Y3BfDfx

submitted by /u/p90036
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From the top plumbing contractor Vancouver WA 98682