We have a fairly new GE Osmonics potable water skid.  We cannot attain full automatic operation because our sodium hypochlorite pumps become gas bound when they sit idle for more than several hours.  We are using Prominent GALa model 1601PPE200UD112100 pumps.  With the normal pumps heads we would have to reprime the pumps each time they sat idle to attain chlorine injection.  We switched over to auto-degas heads and these did not seem to work either.  We raised the chemical tote level up so we have a minumum of 18 inches of head pressure on the suction.  We also curled the tubing on the suction line to provide a hight point for the gas to accumulate before being pumped through.  No gas is visible in the tubing until the pump starts and it draws gas through an approximate 2 foot PVC header upstream of an isolation valve.  The system is tight with no leaks.  Once the pump is primed and the gas is pumped through, it functions well.  What causes the off-gassing?  Should we put a check valve on the suction line at the header to maintain the suction under pressure?  Would a vent line on the suction header help?  We currently use 1/4" tubing on the suction and discharge of the pump per the vendor manual.  We larger tubing help? 

You should set the pumps very close to the hypo tank (less than 2 feet) and use a large diameter for the suction pipe between the tank and the pump (typically 2"). That way the bubbles will get back to the tank and not accumulate in the suction pipe.
Hypo will always degas so this is fairly normal. High temperature will accelerate the degassing.
Also do not forget that for Prominent Gala with NPB (self degassing) head, you shoud not go under 30 % stroke lenght otherwise the volume pumped each time is too small and the degassing device does not work well or at all. Better to use the pumps at 50 % stroke min or at max stroke length if possible.

one of my Midwest clients had same problem & tried a series of retrofits with vent hoses routed back to bulk storage tank. Bulk storage tank adjacent to pump had vent, but tranfser pipe to pump was not "sloped" back UP to the tank.

"crystallization" build-up in vent hose restricted  performance.

finally switched from WT diaphragm metering to Watson-Marlow "tubing" pump for sodium hypochlorite feed.

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