VII. SYSTEM MAINTENANCE & DATA COLLECTION
Page - 45
If the RO unit is to be out of service for more than 4 months, the membrane
elements should be removed from the pressure vessels and stored in airtight
plastic bags in a dark area with temperatures in the 35 to 65
F range. The
membrane elements can be stored in this way for up to a year.
% Glycol by
Volume
Specific Gravity
15.6
C (60
F)
Freezing Point
(
C)
Freezing Point
(
F)
5
1.004
-1.1
30
10
1.006
-2.2
28
15
1.012
-3.9
25
20
1.017
-6.7
20
25
1.020
-8.9
16
30
1.024
-12.8
9
35
1.028
-16.1
3
40
1.032
-20.6
-5
45
1.037
-26.7
-16
50
1.040
-33.3
-28
Table 7-1: Freezing Point of Propylene Glycol / Water Mixtures
The following procedure should be used to protect your RO unit during long
term shutdown.
Use extreme caution when handling preservation chemicals. Always read the
Material Safety Data Sheets and follow their recommendations.
Mix sufficient solution to displace the water in the RO unit. You can estimate
that you will need approximately 4.5 gallons per 8” membrane element or 1.2
gallons per 4” element. Add to this volume another 10% for associated piping.
Mix 4.2 lbs of sodium bisulfite per 100 gallons of water to obtain a 1%
solution.
Do not use sodium sulfite solutions more concentrated than 1% or damage to
the RO unit will result.
Fill the cleaning skid tank (See Section 6) with the appropriate amount of RO
product or DI water.
Add the powdered sodium bisulfite to the water in the cleaning tank and adjust
the valves to the recirculate position. Run the cleaning skid pump for at least
five minutes to allow time for the sodium bisulfite to recirculate and
completely dissolve. Shut off the pump.
Close the RO unit pump discharge throttling valve to prevent the solution from
entering the RO pump. Connect the supply hose from the cleaning skid
discharge to the cleaning port on the RO first stage feed manifold. Connect
two more hoses from the RO product and reject lines back to the cleaning skid
tank. Close the proper valves in the product and reject lines to prevent any
solution from going into the product line to the storage tank. Open the reject
throttling valve on the RO unit. Most of the cleaning solution will recirculate
