First-floor shower trickle in a 14-year-old GI riser: pressure problem or restriction?
A two-storey house in Jaipur is supplied from a 1,000-litre HDPE overhead tank whose outlet sits 7.5 m above the first-floor shower rose. The service drops from the tank in 20 mm GI (medium class) and reduces to 15 mm GI at the first-floor branch; the riser is 9 m long with five elbows and was installed 14 years ago. The owner complains that the first-floor shower gives only a trickle and the basin tap on the same floor is weak, while the ground-floor tap flows strongly and the ground-floor cistern fills normally. A local mechanic has quoted for a 0.5 HP booster pump to be fitted on the riser. Before agreeing, the owner wants a second opinion. A pressure gauge screwed onto the first-floor basin tap reads 0.62 bar with every tap closed, and falls to 0.15 bar when the shower and the basin tap are opened together.
1. Using the gauge readings, decide whether this is a supply-pressure problem or something else. Show the arithmetic and state what each number proves.
Read the worked answer
Convert head to pressure. 1 bar ≈ 10.2 m of water, so 7.5 m of static head = 7.5 ÷ 10.2 ≈ 0.74 bar available at the first-floor outlet with no flow.
Read the two gauge figures.
- Closed: 0.62 bar ≈ 6.3 m. Close to the calculated static head; the small shortfall is gauge tolerance, a partly closed gate valve or a slightly choked tank outlet strainer. It proves the tank head does reach the first floor.
- Flowing (shower + basin together): 0.15 bar ≈ 1.5 m.
- Head lost across the riser and branch = 0.62 − 0.15 = 0.47 bar ≈ 4.8 m.
Interpret. A shower and basin together draw perhaps 0.2–0.3 L/s. Clean 15 mm GI over 9 m with five elbows would lose roughly 0.5–1.5 m at that flow, so 4.8 m is three to eight times too high. A 6.3 m static head comfortably exceeds the ~5 m (0.5 bar) normally wanted at a shower rose. The pressure is therefore adequate; the loss is abnormal, which points to internal encrustation of the old GI, a choked filter washer or aerator, a half-shut valve or a flattened section - all local to the first-floor run, consistent with the healthy ground floor.
Conclusion. A booster pump would push against the same restriction, add electricity and noise, and mask a curable defect. Diagnose and clear the restriction first.
2. Give an ordered diagnostic sequence, cheapest and least invasive first, naming the test that confirms or eliminates each suspect.
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- Fixtures first. Remove the shower rose and the tap aerator/filter washer, check for grit and scale. A blocked rose alone can mimic a whole-line failure. Confirm by refitting only the rose after cleaning and re-measuring flow.
- Quantify the flow at ground-floor and first-floor taps using a bucket and stopwatch (litres per minute). A first-floor figure far below the ground-floor figure on the same supply proves a riser/branch restriction rather than a supply fault.
- Valves and strainers. Check the tank outlet gate valve is fully open (count turns) and clean the strainer/sediment bowl at the tank outlet. Re-test after each single change so you know what fixed it.
- Air lock check. With the branch isolated at the tank and the lowest tap open, crack the union at the high point. A rush of air followed by steady water confirms an air pocket; a permanent high loop in the branch is the usual cause.
- Prove encrustation. Isolate, drain, and dismantle one 15 mm section near the top of the riser. Cut a short length open: a bore reduced by hard scale and iron oxide is conclusive. Also feel along the run for crushed or kinked pipe and count elbows.
- Only then consider the pump, and only if a clean, correctly sized line still gives under about 0.5 bar at the fixture.
3. Recommend the corrective work with the best cost-benefit, and one maintenance step that prevents a repeat.
Read the worked answer
Corrective work, in order of value:
- Clean or replace the tank outlet strainer and the fixture filters.
- Replace the corroded 15 mm GI first-floor branch and riser section with 15 mm CPVC (or 20 mm if two fixtures run together), using long-radius bends or 45° elbows instead of five tight 90° elbows. GI laid 14 years ago in hard water is usually the root cause; replacing the restricted section removes roughly 4 m of the 4.8 m loss.
- Refit the branch without a high loop so it rises continuously from the take-off, letting air escape forward rather than trapping it.
- Keep the booster pump as a last resort, and if a pump is ever needed, fit it on the delivery side with a small pressure vessel so it does not cycle.
Maintenance step: flush the line and clean the tank-outlet strainer and fixture aerators every six months, and keep the tank covered so grit and scale-forming debris do not enter the service pipe. Note in the owner's record the measured static and residual pressures so any future drop can be compared against a baseline.