Low pressure in condo building

[fafaforza]

Hi there, new user.

I'm in a 7 story condo building in Brooklyn. We get a steady 70psi from the city, but pressure out of the booster pump can drop to under 30 in the mornings as everyone uses water.

Our pump is 1.5hp IIRC. The building was built in 2004. The builder was a bit of a schemer: he zoned it as some kind of a school, which allowed him to build 7 stories in an zone with a limit of 6 at the time.

So I am trying to figure out whether
- the pump needs to be refurbished, or
- whether we need a bigger pump on account of the floor discrepancy.

It might be possible the plumbers did their calculations based on 6 floors, and there have been complaints about pressure going back at least 5 years. So I'm not sure it's due to wear.

I've asked a few plumbers, they all gave me different and non specific answers. One guy came over, cleaned some gunk off rubber diaphrams and stuff (nothing was cut or damaged) and told me he'd research it further and get back to me. Never did.

So I am at a loss as to whether I should be asking a plumber, or a plumbing engineer, or a building engineer to figure out what the problem is. I understand one calculates the requirement based on floors, apartments, pipe size, etc. I'm not sure if a plumber does that, or some kind of an engineer.

 

[phishfood]

I am from Florida, so things might be somewhat different in NYC.

But I can tell you in my area that such things are calculated by an engineer. Nothing in the journeyman or master's plumbing test requires such knowledge.

 

[Caduceus]

An engineer may be needed for this one. There are a number of facts that are needed to install the appropriate pump.
You are correct about the info that is needed. How many individual units are on each floor? How many plumbing fixtures are in each unit? What is the size of the existing pipe (volume is also a consideration, not just pressure, during times of high use)? Does each unit have laundry rooms or is there a central laundry in the basement or floor to floor? Make sure these questions, and more, are asked so that you don't buy into a replacement pump that is inadequate.
From what I can already assume, and I could be wrong, you would need a 5HP booster pump with a minimum 3" supply pipe with a regulator before the pump to avoid high pressure cut out from the city side and individual regulators on each branch to the tenants units on the lower floors to avoid high pressure that makes up for the need on the higher floors. Much care is needed on the installation so that a conflicting pressure situation isn't created and the building's RPZ backflow device operates normally.
A plumbing engineer on site should be able to figure this all out for you and it can get very expensive. I agree that you should avoid the average plumber you may find in the yellow pages.

 

[fafaforza]

Thank you for the answers. I'll start a search for an engineer. Hopefully just getting a horsepower number for the pump required won't be too expensive.

 

[Caduceus]

Just don't forget about the pressure regulators. To provide approx. 50 psi to the top floor, you may need 80 psi from the pump and the lower floors could have high pressure issues with toilets, dishwashers, ice makers, etc. and open up another whole world of problems.