Mark & Debbie Mueller
As it has been said earlier in this post hydrocarbons (oil, fuel, etc.), chlorine, and over pressure are by far the biggest killers of RO membranes. Operationally, never exceeding the rated capacity of the water maker based on the flowmeter and never exceeding the maximum pressure as shown on the gauge is the rule. If in a brackish water situation maximum flow will be achieved at far lower pressures than what would normally be seen in the “green” pressure zone i.e. it takes less pressure to make RO water when there is less salt in the feed water.
The way you described the operation of your water maker seems to meet all the manufacturer’s recommendations; you might look to an over pressure condition. According to Dow a major manufacturer of the membranes the nominal operating pressure is 800 psig (55 bar). If you could get a pressure gauge that shows actual pressure & connect it to your system you could verify that your Dessalator gauge is reading accurately and not showing a lower than normal pressure reading causing you to apply a higher than recommended pressure causing damage to the membranes.
Brass Ring A54