I moved into a 4 story apt. building and have very poor water pressure. The owner hired a guy to install a gravity tank on the roof and he connected it to the line in my apt.

The problem is, he used a 300 gal. tank, and ran 3/4 PVC 17' with 6 90deg elbows.

Needless to say we still have poor water pressure. What needs to be done to raise the water pressure in the apt.

I would like to know the pressure at the outlet of the tank.
The loss due to friction.
The pressure at the tie in to the house.
Also what needs to be changed to solve the problem?

Thanks for your help.

That many elbows in 17 ft. isn't a good layout. What you didn't tell us is where you are located, 1st or 4th? That would make a big difference in your pressure. We have no idea as to pressure, that has to be measured or calculated and depends on the head above the pipe. Volume in a 3/4" pipe is only .023 gallons per foot of pipe. Couple that with 6 elbows and not much pressure.

You can complain to the owner but you can't do anything to the building. Understanding water pressure & water tank stand height | Rainharvest.co.za

17 feet tells me this tank is likely on your rooof or one floor above you. That will never produce normal 40 psi. What was the psi prior to the tank installation

It would have to be about 100 feet up to produce 40 psi.

The elbows have very little to do with your issue. Have you measured your psi? This could be a volume issue rather than pressure. Is it bad at every single faucet?

Bottom line! 17 feet and anoher 5 feet for the height of the tank would only give you a little over 9.5 PSI at the tap. Don't worry about friction loss,
What you need is a check valve on te outlet of the tank plus a booster pump and bladder tan k to give you the pressure you desire. Good luck, Tom

I think that's about right.