First-Floor Shower Weak While Ground-Floor Taps Are Strong
A two-storey house is connected directly to a 20 mm municipal service line. The static pressure at the meter is 2.2 bar. The ground-floor kitchen tap flows strongly, but the first-floor shower is weak and becomes a trickle whenever the kitchen tap or washing machine is opened. The first-floor bathroom is 6 m above the meter and is fed by a 12 m long, 15 mm CPVC branch with six elbows; the rest of the house is in 20 mm CPVC. A gate valve at the branch take-off is fully open. The owner has been advised by a neighbour to fit a 0.5 hp booster pump on the service line. Before quoting, you must establish whether the problem is pressure, flow, or a restriction, and avoid a pump that may draw air or cycle. The municipal supply is intermittent, with a 500 L overhead tank filling at night.
1. Describe the measurements and simple checks you would make to separate a pressure problem from a flow or restriction problem. State the expected readings and what each result would prove.
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Measure static and residual pressure at the first-floor shower outlet with a pressure gauge, and measure flow with a 20 L bucket and stopwatch. Static pressure should be roughly 2.2 − (6 × 0.098) ≈ 1.6 bar. If static pressure at the first floor is already below about 1.0 bar, the supply or service line is the problem. If static pressure is near 1.6 bar but drops sharply when the shower and kitchen tap are opened together, friction loss in the 15 mm branch is the problem, not municipal pressure. Record the drop and the fill time. Check the branch gate valve for a broken spindle, the meter strainer for debris, and the shower cartridge filter. Compare the first-floor outlet with a 20 mm garden tap: if the garden tap holds pressure while the shower collapses, the 15 mm branch is undersized or partly blocked. A pump should not be proposed until these readings are known.
2. Recommend a cost-effective remedy and explain why the proposed 0.5 hp booster pump on the service line may be inappropriate.
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The most likely fault is an undersized 15 mm branch: 12 m of pipe with six elbows has a high equivalent length, and 15 mm cannot deliver a comfortable shower flow without a large pressure drop when other fixtures are used. Replace the branch with 22 mm CPVC from the take-off to the bathroom, renew the gate valve, and keep the run as straight as possible. This lowers velocity and friction and is cheaper and more reliable than a pump. A 0.5 hp pump installed directly on an intermittent municipal line can create negative pressure, draw air, run dry, and cycle noisily; it may also violate the supply authority’s rules. If a pump is still needed, install it after the 500 L tank with a low-level cut-off, a pressure switch, and a small diaphragm tank to reduce cycling. Recheck static pressure after the upgrade; if ground-floor pressure exceeds 3 bar, fit a pressure-reducing valve.
3. If the owner insists on keeping the existing 15 mm branch, what operating limits and risks should you explain before any pump is fitted?
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With 15 mm pipe, simultaneous use of the shower, kitchen tap, and washing machine will always cause severe pressure loss. The branch can carry only a small flow at acceptable velocity, so a pump may raise pressure but cannot create enough flow; it will tend to cycle or cavitate. Explain that the shower will still falter when other outlets open, and that the pump may shorten the life of the CPVC fittings and cause water hammer. If the municipal supply is intermittent, the pump must not be allowed to run dry; a dry-run protection device and a break tank are essential. Give the owner a written comparison: branch replacement gives a permanent low-maintenance solution, while a pump on the existing branch treats the symptom and adds electrical and maintenance risk.