I want a decent 4040 membrane. I normally buy from vyair but last 1 I got didn't last as long as the last couple I had .my water pressure is really high
The first question Doug will need answered is what your water pressure is. A pressure gauge is available from Screwfix and/or Toolstation.
I've had excellent service from my Axeon HF5 membrane. It's still producing pure at a 97% rejection rate. It's 12 and a half years old. But it is producing pure really slowly now, so probably needs replacing shortly.