The product is marketed as an “indistructable” sand-filter for use in swimming pools and comes with a 10 year warrany. Supposedly the manufacturer has a 40 year track record of designing and improving these “top quality” things.. 
Based on my limited personal experience I’d confirm that the product will indeed reach the 10 year lifespan but I am still very disappointed by what I deem to be a very poorly designed product – if not to use the term “planned obsolescence”. The common failure point of this product supposedly cannot be repaired (according to my pool repair shop) and when broken, a replacement will set you back around 1’500€ – i.e. you are supposed to buy a new one:
The weak point of the design (which all the products of this manufacturer that I came across seem to share) is the “screw in” plastic lid – in particular the threads that are cut into the brittle fibreglass material: It comes as no surprise (except maybe to a manufacturer with 40 years experience with this kind of thing) that over time the pressurization/depressurization cycles will cause those threads to wear out and at some point they will just no longer be able to hold down the lid under pressure.
At that point you will wake up some morning and find that your pool is suddenly completely dry – and if you are unlucky your pump may also have died as a collateral damage due to having been run without water.
I am probably not the typical “consumer” but I find it inacceptable if this kind of expensive product is deemed to be a “wearing part” that needs to be completely replaced every 10 years. Especially if everything except the garbage fibreglass threads is still perfectly fine. I think it should be noted that when you look at “pressure vessels” that are used in other context you will find that this kind of “lid design” doesn’t seem to be used anywhere else. I wonder why that might be the case… I meanwhile found that there are other pool filter manufacturers that seem to be using designs that to me look much better/durable. Specifically designs where the lid is clamped down on the neck of the filter. I don’t know if those products come with other problems of their own but I’d definitely stay away from the Triton garbage.
So much for why you should not ever buy this kind of garbage product!
But since my “pool repair shop” had also told me that he had heard about people that had succeded by tinkering to workaround the problem, I decided to give it a try myself. The below is my “proof of concept” but it still remains to be seen if it will actually pass the test of time (I am a bit worried that the plastic lid might eventually shatter).
The idea of my hack is to have some additional support for the plastic lid to push it down from the top (supporting what remains of the original “fibreglass thread design”). To that end I drilled six 6mm holes into the top of the fireglass container and glued respective M6 screws in place with epoxy. (I am using A4 stainless steel screws and washers from a boating supply store).
On the inside of the container I covered the washers/screw-heads with several layers of fibreglass/epoxy – trying to maintain the tightness of the container.
In order to still being able to “screw on” the plastic lid, I had to cut off the original handles of the original tool and replace them with handles that are able to clear the screws that now stick up from my sand filter:
As a means to hold down the lid I went for a sturdy steel plate. (I guess it helps if you have somebody with a water-jet or laser cutter at hand in order to produce that.)
And after some epoxy painting here is the finished product (I had designed the plate with extra holes that I could use as a template/guide to drill into the fibreglass container):
