Water Meter and Service Size 1

[CPENG78]

Hello Everyone,
A quick question. The California Plumbing Code table 6-6 provides you with the available number of fixture units that can be assigned to a water meter and service line based on a maximum allowable length.

This table however goes up only to a 2" meter with a 2.5" service. I have a project where I have to consider the use of an existing 3" meter and service to provide domestic water to an existing site where a few new smaller buildings will be added.

Does anyone outer have experience on what the code states for meters and service lines that exceed the values on the table?

 

[fel3]

I don't have the full code handy (only the fixture unit info), but I've designed lots of larger services. If the code stops at a 2" meter, then you enter the territory of BPJ (Best Professional Judgment).

You probably already know the following procedure, but just in case…

[1] Determine what the ultimate peak flow will be on the water service (or have the plumbing engineer do that). If you don't know what demands the future buildings will generate, then be conservative. If you can make a reasonable estimate of the total number of fixture units the service will have to support, then you can use the graph in the plumbing code to come up with a rough estimate of peak flow. Then add a safety factor.

I have worked on prison sites with >3000 FU. We size the water system and individual building servies by cross-checking the plumbing engineer's FU-based demand estimates with historical data for similar prisons. I generally don't like to rely on just fixture units.

With respect to using FU, you should to look at this two ways:
(a) Building services should be based on individual building FU & preak flow values.
(b) Sizing the upstream end of the service should be based on the total FU count, converted to peak flow. The upper part of the demand load curves in the plumbing code are approx Qp=2.07*(FU^0.67) so you cannot add individual peak flows to get the total peak flow.

[2] Have the plumbing engineer specify a minimum pressure where the water service enters the building. He should be able to do this based on the number of floors, the types of fixtures, the interior plumbing, etc. He should have done some calcs to determine this pressure. Take his number add a little as a safety factor, maybe 3 to 5 psi.

[3] Determine what the water system can provide at the upstream end of the new water service. This may be provided by the water system owner, estimated from flow tests, estimated from a network model, etc. Hopefully, the pressure on the upstream end of the water service is higher than the plumbing engineer needed. Otherwise, a pump may be in your future.

[4] If you are running the network model, I suggest including your service (including minor losses for the meter, bends, etc) and peak demands in the model. That's the easiest way to figure this out. If not, it's still a pretty simple manual hydraulics calc to check a 3" service to see if it works. If not, try 4", etc. I suggest starting with a preferred velocity at peak flow, sizing the pipe based on Q and V, then seeing if that works pressure wise, If not, go one size larger.

[5] Since you're outside the code, be prepared to show your calcs to the approving agency.

I hope this helps.

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