Feed pumps water hammer

Pumps should be started slowly to prevent water hammer (a surge resulting from a sudden change in liquid velocity). Water hammer can cause cracks in the outer shell of the membrane modules as well as compaction of the membrane itself (compaction results in lower flux through the membrane at constant pressure). Also, water hammer causes the membrane modules to move in the vessel, which can cause wear to the O-rings used on standard interconnectors and lead to leaks of feed water into the permeate (see Chapter 4.3.3). An increase in pressure of no more than 10 psi per second is recommended.3 Some motors may be equipped with a "soft start" that regulates the speed with which they start up. Other considerations to minimize water hammer include ... 

Membrane compaction involves the compressing of the membrane itself that, in essence, makes the membrane denser or thicker which reduces the flow and salt passage through it. Compaction can occur under higher feed pressure, high temperature, and water hammer. (Water hammer occurs when the RO high-pressure feed pump is started and there is air trapped in the membrane modules—see Chapter 6.2.) Most brackish water membranes, when operated properly, experience a minimal degree of compaction. However, seawater membranes and cellulose acetate membranes... 

Fig. 12.9. Flow diagram for manufacture of cellulose acetate yarn (1) wood pulp (2) attrition mill (3) cyclone (4) 35% acetic acid (5) pretreater (6) magnesium acetate solution (7) precooled acetylation mix (8) sulfuric acid (9) acetylator (10) ripener (11) steam (12) blender (13) precipitator (14) dilute acetic acid (15) hammer mill (16) water (17) rotary screen washer (18) squeeze rolls (19) drying oven (20) blender (21) storage bins (22) silos (23) weight bins (24) acetone (25) wood pulp (26) pigment (27) mixers (28) hold tanks (29) filter press (30) pump (31) filter (32) air (33) jet (34) acetone recovery (35) oiling wheel (36) feed roll (37) bobbin (38) inspection.

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