Reverse osmosis watermaker preventative maintenance

There is a huge demand for potable water in offshore vessels and especially on drilling platforms and similar semi-permanent operations where it is sometimes needed to support production processes as well as providing clean fresh water for drinking and washing. With limited access to spare parts whilst offshore, and few opportunities to carry out maintenance that might break continuity of water supply, ensuring the reliable operation of water makers is crucial.

Reverse osmosis water makers such as the Pure Water Series offered by Parker Hannifin offer important space, energy efficiency and emissions benefits vs some existing approaches such as steam powered units. They also have a relatively simple and robust principle of operation meaning they will run reliably, without attention, for extended periods. However, it is still important for operators of sea going craft and offshore rigs to be aware of and implement preventative maintenance.

Below are the key water maker maintenance issues that should be considered:

As with any plant equipment, all mounting hardware plus belts, hoses, connections pressure gauges and flow meters should be periodically visually checked. In addition, operators should check bolts, screws and brackets for tightness. Hoses should be inspected for wear and that they are not chaffed or in contact with other surfaces that may cause abrasion. Another quick yet important check is for leakage of oils or water; finding salt residue could also indicate a leak of water.

The oil level in the high pressure pump crankcase should be checked when the pump is horizontal. The high pressure pump oil should be changed after the first 50 hours of operation post commissioning and every 500 hours thereafter.

Operators should test the seacock on the intake through hull for proper operation. Before the system is run it is important that that the seacock is in the OPEN position and that any overboard valves or product water valves are also open. In addition, the water maker intake through the hull should be checked to ensure there are no restrictions or obstructions to the flow.

It is recommended that pre-filters on the water maker be replaced when the inlet pressure drops to 1 psi or below. Parker Village Marine pleated polypropylene filters are designed to last longer than lower cost string bound pre-filters and will typically provide a more cost effective approach overall with lower pressure drops and higher flows for longer. When changing the filter element it is important to clean the bottom of the filter housing thoroughly.

As a safeguard, users should look to replace the fresh water flush carbon filter element to ensure no chlorinated water enters the system potentially causing damage to membranes. Furthermore, it is important to test the fresh water flush line to make sure that water from the fresh water tank reaches the water maker during the fresh water flush cycle to confirm that no valves have been shut and the line is free from obstructions.

If the system uses a needle valve pressure regulator it should be backed off fully. The system should never be started in the high pressure position as this may result in damage to the system. Start the low pressure pump on the system and let seawater circulate through the system for 5 - 10 minutes after which the high pressure pump can be started. Then turn the needle valve to gradually increase the system pressure until the system is making its rated product water output or 800 psi is reached - whichever comes first.

Once the system operation is complete and working effectively, it can be shut down, the regulator valve turned anti-clockwise to the completely open position, the high pressure pump turned off followed by the low pressure pump, before the fresh water flush is run.

Written by Allan Cousins, UK Product Sales Manager Hydraulic & Racor Filtration, Parker Hannifin

Read the article online at: https://www.hydrocarbonengineering.com/special-reports/04072013/reverse_osmosis_watermaker_preventative_maintenance_016/