How does reducing the pipe diameter downstream of a tee affect zone pressure?

• A. It increases friction loss and reduces downstream pressure.
• B. It has no effect on pressure.
• C. It improves flow without affecting pressure.
• D. It decreases friction loss and increases downstream pressure.

Answer: (A)

Reducing pipe diameter downstream of a tee increases friction losses and the overall head loss, which lowers the pressure available at the downstream zone. The same flow must pass through a smaller cross-section, so velocity rises (Q = A × V). Higher velocity raises friction losses along the downstream run, and the change in diameter adds a local loss at the transition. All these losses add up as water moves downstream, so the pressure you measure at the zone drops. If you want to keep zone pressure higher, you’d need to widen the downstream pipe or reduce the flow, rather than expect pressure to rise from the restriction.