Tuas factory unit siphoned water back: valve installed backwards
A Tuas factory unit started leaking water back through its drain pump days after a routine service. Port-side industrial sites here often plan access around shipping schedules, which can rush reassembly steps. A valve installed backwards is easy to miss until the leak actually starts.
By Team Snowflake | Reviewed 11 Jul 2026
Case summary
Daikin Ducted5 years oldIndustrialTuas, Singapore
- Concern
- The facilities manager worried the drain pump itself had failed and would need full replacement so soon after a service visit.
- Found
- Drain pump's non-return valve installed backwards during the last service, letting water siphon back
- Key check
- Checked the valve's orientation before assuming the pump itself had failed
- Result
- The backflow stopped completely once the valve was refitted the correct way round a few days later. The facilities manager avoided paying for pump replacement that the actual fault never required in the first place.
What we were told
The facilities manager said water appeared to flow backward through the drain line each time the pump cycled off, leaving a small pool near the unit. This started about a week after a routine service visit. Nothing else about the unit's operation had changed around that time.
What we checked
We treated the timing after the service as the strongest lead rather than assuming the pump itself had failed. A genuine pump failure usually stops clearing water altogether. Water flowing backward specifically after the pump cycles off points at a valve fitted the wrong way round instead.
The drain pump itself ran normally throughout and cleared water at its expected rate while actively running.
The non-return valve on the discharge line had been installed facing the wrong direction entirely.
Water was able to flow back through the reversed valve once each pump cycle ended for the day.
No other part of the pump assembly or drain line showed any separate fault of its own.
What we found
During the last service, the non-return valve on the pump's discharge line was refitted facing the wrong direction. While the pump was actively running, this made little difference, since the pump pushed water through regardless of the valve's orientation. But once the pump cycled off, water in the line was free to flow back through the reversed valve instead of being held in place, pooling near the unit each time it happened.
What fixed it
We refitted the non-return valve in the correct orientation and confirmed water no longer flowed back once the pump cycled off. We did not recommend replacing the pump, since it was working correctly throughout the visit. We advised checking valve orientation specifically at every future service, given how easy it is to reverse during a routine reassembly.
Outcome
The backflow stopped completely once the valve was refitted the correct way round a few days later. The facilities manager avoided paying for pump replacement that the actual fault never required in the first place.
What this case teaches us
Water siphoning back after a service often means a reversed valve, not pump failure
- Water siphoning back through a drain pump soon after a service often means a valve was fitted backwards.
- A non-return valve installed the wrong way round can let water flow back once the pump stops running.
- Ask whether the valve's orientation was checked before any pump replacement is quoted after a service.
Related reading
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