[markymark]

I'm looking for advice from any other users of a 4021 or 4040 r/o set up.
I've come to change the membrane on mine, and on refitting it the inlet end cap keeps popping off under pressure. I've checked my set up against the sellers suggestions, I've checked all my fittings, I've tightened the housing clamps beyond belief.  All the inlet and outlet hoses and fittings are clear. I've even sacrificed a couple of chickens to the gods but the same thing happens every time. Even bought a new housing to eliminate the chance I had distorted the original housing. End result? The inlet cap pops off every time.
Anyone have any idea what the problem could be?

[CleanClear]

What sort of housing is it ? Is it one of them white Cobra ones  with black endcaps ?

[markymark]

My bad....
It's the stainless steel housing.

Which is really slippery when you're trying to fettle it in the rain. As my knuckles will attest.

[markymark]

Sigh.....
Problem solved courtesy of the fine folks at Vyair.
For the hard of thinking (yes, I mean me) I was placing the housing clamps over the wrong part of the body ie not clamping the housing AND the end cap.
So I had removed them without noticing the bl00dy obvious set up. And replaced them without noticing the bl00dy obvious.
I am a buffoon.

[Jonny 87]

We’ve all been there. 

Atleast it’s sorted.

I changed my 4021 for the first time this year, it was a bit awkward, but now I’ve done it once it’ll be no problem going forward.

You’ll be in the same boat now. Live and learn.