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Calculate water pressure based on elevation difference, pipe friction loss, and flow rate. Determine available pressure at fixtures.
Water pressure in a plumbing system is affected by three main factors: the supply pressure from your water source, the elevation change between the source and fixture, and friction losses in the pipes and fittings.
Pressure from elevation. Water loses 0.433 PSI for every foot it rises.
Pressure when water is flowing. Affected by pipe size and flow rate.
Pressure lost to pipe walls and fittings. Increases with flow rate and pipe length.
Example: 50 ft elevation = 50 × 0.433 = 21.65 PSI loss
Where L = length, Q = flow (GPM), C = roughness factor, d = diameter
Ideal velocity: 4-8 ft/s. Above 8 ft/s causes noise and erosion.
| Pressure Range | Status | Action |
|---|---|---|
| Below 20 PSI | Too Low | Install pressure booster pump |
| 20-40 PSI | Low | May need booster for upper floors |
| 40-60 PSI | Ideal | No action needed |
| 60-80 PSI | High | Consider pressure reducing valve |
| Above 80 PSI | Too High | Install PRV (code required) |
Normal residential water pressure is 40-60 PSI. Most plumbing codes require pressure reducing valves when supply pressure exceeds 80 PSI.
You lose approximately 0.433 PSI per foot of elevation. A typical floor height of 10 feet equals about 4.3 PSI loss.
Low pressure can be caused by: high elevation, undersized pipes, clogged pipes/aerators, partially closed valves, or low municipal supply pressure.
Options include: checking/opening main valve, cleaning aerators, upgrading to larger pipes, or installing a pressure booster pump.