Operation, Maintenance, Troubleshooting and Repair
What the exam tests here
Fault-finding logic: reading pressure and flow together to locate a problem, then repairing it without creating a second one.
Core rules
- Preventive work: backwash filters on pressure difference, flush laterals monthly, chlorinate where biofilm or iron is present (continuous 1–2 ppm; shock dose 50–100 ppm for 30–60 minutes, then flush), and acidify to pH 2–3 for carbonate scale.
- Low head pressure with normal flow suggests a partly closed valve or a worn impeller; low flow with normal pressure suggests a blockage downstream.
- Low pressure at the tail with correct head pressure means excess friction, clogged laterals or too long a run.
- Common faults: emitter clogging from filter failure, algae or iron bacteria; rodent and root damage; leaking joints; cavitation noise from a blocked suction; pump overheating from a closed delivery valve.
- Repairs: joiner for a cut lateral, goof plug for a wrong punch, repair clamp for PVC pipe, and replacement emitters of the same discharge class.
Worked example
A farmer reports weak emission at the tail. The head gauge reads 1.2 kg/cm², which is normal, tail flow is poor, and the filter pressure difference is 0.9 bar. Reasoning: the filter is well past the 0.5–0.7 bar backwash point, so flow is throttled and pressure is lost through the clogged media; downstream laterals also received dirty water. Action: backwash or replace the media, flush all laterals, re-measure EU, and restore the backwash schedule.
Traps that cost marks
- Raising pump pressure to "solve" a blockage.
- Chlorinating and acidifying at the same time; chlorine loses strength and dangerous gas can form.
- Fitting a replacement emitter of a different discharge rate, which disturbs uniformity.
- Recording the repair without noting the cause, so it recurs.
Quick recall
Pressure plus flow tells you where the fault sits.