The Hypochlorite Suction-Path Blueprint

Sodium hypochlorite decomposes on its own and releases gas. Tacmina publishes the decomposition as 2NaClO to 2NaCl + O2 and describes hypochlorite as a chemical that readily decomposes into a gas. Blue-White describes the same behavior from the pump side, noting that chemicals which offgas can create air pockets that cause vapor locking. A reciprocating metering pump moves a fixed displacement per stroke and depends on an incompressible liquid; when a gas pocket occupies the pump head, the stroke compresses and expands that pocket instead of pushing chemical through the discharge check. Tacmina calls the end state gas lock, where no liquid is discharged at all even with a reciprocating diaphragm.

A published US wastewater plant case reports pumps that worked satisfactorily at higher chemical flow rates but repeatedly vapour locked at lower flows. At a low stroke rate, gas enters the pump head at the rate the chemistry produces it while the pump sweeps the head far less often, so gas production outpaces gas removal. Blue-White describes the same mechanism when it warns that on an oversized or too-slow pump, gas can accumulate in the pump head without being pushed through. This is why installing a larger pump usually makes the problem worse rather than better.

If the pump runs correctly right after you manually bleed it, then gradually loses output, and bleeding the head again produces a slug of gas followed by chemical, suspect gas binding before the diaphragm or the calibration. A failed diaphragm does not restore full output when you bleed it.

Poly Processing names iron, copper, cobalt and nickel as accelerators of hypochlorite degradation, and its own general specification for 9 to 15 percent sodium hypochlorite states that an IMFO outlet is strongly recommended for full drainage of sodium hypochlorite to prevent sediment build up. Poly describes the Integrally Molded Flanged Outlet as a homogenous flange system molded as part of the tank, positioned at the bottom of the sidewall below the tank knuckle radius, which it says gives full tank discharge. A tank that never fully drains keeps a sediment heel where those metals concentrate, and a decomposing heel is a gas source feeding the same suction line.

Blue-White states that peristaltic pumps are very effective when dosing fluids that contain trapped gases because they are not affected by air bubbles, that bubbles simply pass through the pump tube, and that there is no vapor lock and no loss of prime. On the FLEXFLO A3 specifically Blue-White states it cannot vapor lock or lose prime. Both are manufacturer claims with no published test method behind them and should be treated as such. Blue-White does not make a hypochlorite-specific vapor-lock claim on its A3 product pages; the hypochlorite link comes separately from its Flex-A-Prene tube compatibility statement, which describes the tube as chemically resistant to 25 percent sodium hypochlorite.