High Rise pressure issue

[John Blizard]

Hello, I am a building engineer at a 12 story 292 unit condo in DC. One of my owners has pressure variation in various fixtures in his unit. I have seen kitchen faucet cold water pressure drop out, owner reports shower and bath sink also does. He is on top floor. Pressure booster in basement, hot and cold supply loops in 12th floor ceiling, tier shutoffs and individual unit shutoffs inside each apt. CPVC supply lines, galvanized main supply (Victaulic) 4" lines. I am thinking maybe something caught in one of the unit shutoff (ball) valves? No pressure modification in system besides basement booster.
Thanks for your thoughts on this!

 

[hj]

What is the system's pressure? It would need about 64 psi just to get to that level with no residual pressure for the faucets.

 

[Sponsor]

 

[Plumber69]

What is the system's pressure? It would need about 64 psi just to get to that level with no residual pressure for the faucets.

But if it's just the cold he should have good pressure

 

[Valveman]

64 PSI will lift the water to 148'. But then you need to add the 40 PSI needed on the top floor for a total pump pressure of at least 104 PSI. Being on the top floor the water being used on the lower floors can rob the top floor of water supply. My guess is the pumps are variable speed and are reacting too slowly to a reduction in pressure, or they simply do not supply enough pressure.

If the lower floors do not have any pressure control, the bottom floor will have 100 PSI. The lower floors water outlets will put out so much water at 100 PSI, they can steal water and pressure from the upper floors.

If the lower floors are fitted with a pressure reducing valve than only supplies 40 PSI, the fixtures will not use excess water and steal from the upper floors. Plus if your pump control system can maintain a constant 104 PSI, and reacts quickly to any drop in pressure like when using a Cycle Stop Valve instead of a VFD, all floors should have excellent pressure.