OPERATOR, UNIT, DIRECT SUPPORT, AND GENERAL SUPPORT MAINTENANCE
REVERSE OSMOSIS WATER PURIFICATION UNIT FOR
INLAND AND COASTAL LARGE TUG (LT)
OPERATION UNDER UNUSUAL CONDITIONS
One Watercraft Engineer, 88L
SECURITY MEASURES FOR ELECTRONIC DATA
No electronic data is used or stored in the Reverse Osmosis Water Purification system (ROWPU).
The ROWPU may be operated when the ambient raw water temperature is between 33 and 118 F (0.6 and 47. 8 C)
with a maximum salinity content of 65,000 ppm. These conditions cover all navigable waters in which the Large Tug
(LT) is capable of operating. The ROWPU is designed to operate continuously at 900 PSI (62.1 bar). The system
high pressure cutout is set at 950 PSI (65.5 bar) 25 PSI (1.7 bar). Normal benchmark readings for performance are
based upon a raw water temperature of 77 F (25 C) with a salinity content of 35,000 ppm. Although the ROWPU is
designed to operate in all navigable oceans, special considerations must be made by the operator if raw water
conditions stray too far from center. The variables the operator must take into consideration are salinity, temperature,
The ROWPU will produce product water at 100% of rated capacity up to a salinity content of 38,000 ppm. As
seen in table 1, when the salinity content of the raw water exceeds 40,000 ppm, the operator will notice a decline
in the production of product water. This is normal. Do not attempt to increase the rate of product water produc-
tion by increasing system operating pressure, or damage could occur to the ROWPU. Conversely, the operator
will notice that the ROWPU will easily exceed 100% of rated capacity in brackish water. The operator must take
action to lower system operation pressure so that the ROWPU does not exceed 100% of rated capacity.
At temperatures close to freezing, water molecules are less active, and it is more difficult for the water molecules
to pass across the reverse osmosis membrane. The operator should notice that the colder the raw water, the
less product water that can be produced. This is normal, and the operator is reminded to never exceed maximum
safe operating pressure. Conversely, in warmer water the ROWPU could easily exceed 100% rated capacity.
This is normal, and the operator must decrease the system operation pressure so that 100% rated capacity is not
exceeded. Table 2 is used to estimate the effect of temperature on ROWPU product water production.
SYSTEM OPERATING PRESSURE
The upper limit of the ROWPU maximum safe operating pressure is 950 PSI (65.5 bar). The operator should
never exceed 900 PSI (62.1 bar) as indicated on the system operation pressure gauges. The ROWPU is de-
signed to produce product water at 100% of rated capacity at 900 PSI (62.1 bar). Table 3 demonstrates that as
raw water temperature increases, the system pressure must be adjusted so that the system does not exceed
100% of rated capacity. Product water flow greater than rated capacity will cause premature fouling of the
Reverse Osmosis (RO) membrane elements.