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The commissioning faults we see most often

The same dozen faults account for most warranty calls and most "the equipment doesn't work" conversations. A checklist of them, each with its telltale and its five-minute prevention.

Written by the Definitive Water Technologies team · Technically reviewed by Chandré Naudé, BEng (Civil) · Published · Last updated

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  1. Almost every component arrives working. What fails is the installation's assumptions.
  2. Pressures never checked. Settings left at factory defaults. Protective valves left out as "extras".
  3. Syphoning through an unvalved injection point. The tank drains itself. The process gets unmetered chemical.
  4. FKM seals on hypochlorite. Mystery leaks and lost prime within months. Fix: EPDM, stated on the order.
  5. No vacuum breaker on a drainable FRP vessel. The first proper drain-down crumples the liner.
  6. Factory-default valve settings. Regeneration for a resin volume nobody has. Backwash for a different filter.
  7. Chlorinated water reaching the membranes. Spent carbon, missing SMBS, a "temporary" bypass. Permanent rejection loss, in weeks.
  8. No gauges, no sample points. The cheapest instrumentation there is, and the first thing value-engineering deletes.
  9. Rule of thumb: Commission with three tests and a pen. Syphon, free-chlorine and drain-down. Then write every setting on the equipment it belongs to.

Why commissioning is where systems fail

Almost every component arrives working. What fails is the installation's assumptions: pressures never checked, settings left at factory defaults, protective valves omitted as "extras". These are the recurring offenders, in roughly the order they bite.

Dosing and chemical

  • Syphoning through an unvalved injection point. The tank drains itself; the process gets unmetered chemical. Prevention: injection valve at the quill, back-pressure/anti-syphon valve at the pump, and the switched-off syphon test before handover.
  • FKM seals on hypochlorite. Mystery leaks and lost prime within months. Prevention: EPDM for hypochlorite, stated on the order.
  • Doser sized to run at 3% of capacity. Erratic dosing that measurement keeps "confirming and unconfirming". Prevention: the 20 – 80% rule; dilute the chemical.

Vessels and valves

  • Backwash hydraulics never verified. The bed silts, mudballs, channels; the media gets blamed. Prevention: medium's backwash rate × bed area, checked against valve, drain and source before the media order.
  • No vacuum breaker on a drainable FRP vessel. First proper drain-down or syphon event crumples the liner. Prevention: air admittance at the high point, fitted at installation.
  • Factory-default valve settings. Regeneration for a resin volume nobody has, backwash for a different filter. Prevention: programme resin volume, salt dose, hardness and cycle times per the as-built system, and write them on the vessel.
  • Salt-dose economics never set. The softener regenerates daily on a bed exhausted 30%. Prevention: size the interval per the sizing article; volumetric control where use varies.
  • Filter valve on a softener (or a brine cycle left active on a carbon vessel). Hard water on schedule / water wasted on schedule. Prevention: check the brine port and the code's first digit.

Membranes

  • Chlorinated water reaching the elements: spent carbon, missing SMBS, a "temporary" bypass. Permanent rejection loss, measured in weeks. Prevention: free-chlorine test after the carbon at commissioning and every service.
  • Preservative never flushed / first permeate used. New elements ship in preservative; the first production water is not product. Prevention: flush per the datasheet before anything downstream sees permeate.
  • Reused vessel closure seals. Salty permeate immediately after a service visit. Prevention: new seals every opening, and when quality drops post-service, suspect the seal before the membrane.
  • Recovery "adjusted" on site. The concentrate valve gets throttled for more product; the tail scales within the quarter. Prevention: recovery is a design number; lock it, log it, and re-project before changing it.

Disinfection and general

  • UV before the tank, or without its prefilter. The lamp treats water that gets recontaminated, or shadows past half its dose. Prevention: UV last, 5 µm ahead, lamp on the calendar.
  • No gauges, no sample points. A system without them cannot be diagnosed, and every fault above hides longer. Prevention: gauges either side of every filtration stage; a sample tap between every major stage. It is the cheapest instrumentation that exists and the first thing value-engineering deletes.

Rule of thumb: commission with three tests and a pen: syphon test on every doser, free-chlorine test after every carbon stage, drain-down test with the vacuum breaker watched. Write every setting on the equipment it belongs to. An hour of commissioning discipline buys years of not meeting this list again.

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General engineering guidance reviewed by DWT’s technical team. It does not replace manufacturer datasheets or a site-specific design; confirm selections against the actual water analysis and duty conditions.