We do about 2-4 proprietary pressure vessel/membrane swap-outs per month: HRO, VM, Pur. And below is a
photo of a Pur80
project.
Pur80 Original
Pur80 with new 21" Pressure Vessel to accept off the shelf DOW SW30-2540 Membranes
The problem is that not all proprietary membranes can be swapped out for off the shelf membranes. You have to ballance the high pressure pump's flow rate with the membrane area. The PUR35 and 40 simply have too small a flow for the 21" off the shelf membranes, so that leaves people trapped. However, it's a piece of cake with the larger flow
water makers to swap to a 21" or 40" pressure vessel and membrane and be done with the proprietary pricing
game.