Assistance with Commercial Toilet on 3/4" meter supply line.

[Twowaxhack]

Straight from Rehau website
https://www.rehau.com/downloads/497802/pexaplumbingdesignandinstallationguide-855739uscaen-rehau.pdf


The maximum flow rate of 1” pex is 18.8gpm to stay within Rehau design limits. That’s at 10 feet per second velocity. (Cold water)

Most plumbing codes limit velocity to 8 feet per second for pex. That brings the max GPM to 15gpm. (Cold water)

You’re claiming a 37gpm flow rate at 12’ per second. More than double it’s capacity at the approve flow rates.

Sorry but that’s not going to pass. And even if it does operate, it’ll tear itself up eventually.

 

[MicEd69]

In my last response, I just pulled out some tables quickly on velocities and did not notice they were not for PEX. I only use copper on my projects as my work is not based on getting the job done in the shortest amount of time; i.e. plumbing is not how I make a living.

So, for clarity, when both toilets are flushed at the same time, the demand for water will be around 35 GPM for about 5.5 seconds. Since the ID of 1" PEX pipe is only 7/8", the resulting velocity for that 5.5 seconds will be 18.7 FPS. When only one toilet is flushed at a time, the values will obviously be half of those, or 17.5 GPM and 9.35 FPS respectively.

So, during a two simultaneous flush event, the velocity will be way above the recommended maximum velocity for 5.5 seconds. And assuming a 50' pipe run and a couple of 90s, a couple of tees, and a drop ear elbow, you will indeed get close to 60 PSI pressure drop. Starting at 90 PSI, you will end up at 30 PSI, which is above the minimum pressure required to reseat a Flushometer valve.

So, going to 1 1/4" PEX would eliminate the problem of exceeding the recommended maximum velocity for 5.5 seconds in the 1" PEX during the times both toilets are flushed simultaneously. The pressure drop would also be significantly reduced of course. Going to 1" copper would also be an option to resolve the issue that will happen when the toilets are flushed simultaneously.

So, I guess BriarHouseBrew needs to make a decision based on this information. Is this going to be an issue for 5.5 seconds when both toilets are flushed at the same time?

 

[Twowaxhack]

The maximum pressure allowed inside the building is 80 psi.

Not 90

Maximum velocity isn’t to be exceeded. Over time water pressure typically decreases as new customers are added to
The main.

Next year his pressure may be 60 psi and nothing works……..

I make my living installing plumbing everyday. Typically correcting mistakes made by others.

 

[MicEd69]

Yep, Twowaxhack is right. I suggest BriarHouseBrew use 1 1/4" PEX or 1" copper. That will cover this issue and further potential uses.

 

[FishScreener]

The water company is not bound by plumbing code. They can flow 25 gallons a minute through 5/8 copper tubing at 120 psi. They can exceed the allowable flow velocity of the pipe. It doesn’t matter to anyone but them.

The customer is responsible for the piping on the outlet side of the meter and IS bound by plumbing code.

3/4” pipe is simply not large enough to supply a commercial building. It’s can supply roughly 12gpm and it’s flow velocity shouldn’t exceed approx. 8 fps. Or you’ll get erosion wear.

Pressure inside the building can’t exceed 80 psi.

The only 3/4” pipe that has been confirmed in this thread is the original posters main water service coming into the building. So that’s why I said it’s a waste of time to call the water company about THAT pipe.

It’s silly to even be discussing a 3/4” building main with direct flush valve toilets. When pigs fly……..

The EPA, and the State regulators would disagree with you about it mattering only to the utility..

 

[FishScreener]

Yep, Twowaxhack is right. I suggest BriarHouseBrew use 1 1/4" PEX or 1" copper. That will cover this issue and further potential uses.

Zern makes, maybe made, an in wall blow molded poly tank which goes in the wall cavity, tee-d into the feed to the toilet, and holds enough water for two code compliant toilet flushes at, I think 30-psi. It is just a thin plastic tank with inlet/outlet at the bottom, a check valve on the tee feeding it, and the toilet attached to the opposite leg of the tee..

The feed to the check valve could be a 1/4-inch, so long as the pressure is high enough to run the toilets. And the discharge from the tank, and feed to the toilet are large enough. The tank holds the needed volume of water, and then can recharge before the toilet needs to flush again.

The sytem pressure pressurizes the water in the tank, to whatever the infeed pressure is, and dumps it to the toilet on demand. If you have room, I’d recommend just installing a well tank to feed the two toilets. It would do the same thing and allow you to service it if needed. Not that the blow molded tank should ever need service. But with them in the wall cavity, they would be a mess to fix if there were ever any issues.

 

[MicEd69]

Zern makes, maybe made, an in wall blow molded poly tank which goes in the wall cavity, tee-d into the feed to the toilet, and holds enough water for two code compliant toilet flushes at, I think 30-psi. It is just a thin plastic tank with inlet/outlet at the bottom, a check valve on the tee feeding it, and the toilet attached to the opposite leg of the tee..

The feed to the check valve could be a 1/4-inch, so long as the pressure is high enough to run the toilets. And the discharge from the tank, and feed to the toilet are large enough. The tank holds the needed volume of water, and then can recharge before the toilet needs to flush again.

The sytem pressure pressurizes the water in the tank, to whatever the infeed pressure is, and dumps it to the toilet on demand. If you have room, I’d recommend just installing a well tank to feed the two toilets. It would do the same thing and allow you to service it if needed. Not that the blow molded tank should ever need service. But with them in the wall cavity, they would be a mess to fix if there were ever any issues.

Great approach, especially since the issue will only raise its head when both toilets are flushing at the same time. A long at the flushes are not happening in a 5.5 second span, the flows and velocities will be well within design parameters.

Thanks Fishscreener!

 

[Twowaxhack]

The EPA, and the State regulators would disagree with you about it mattering only to the utility..

The EPA and state regulators couldn’t care less how much water the utility companies meter will flow if it meets the minimum.

We are not talking about lead water mains.


And in almost 40 years of plumbing I’ve never seen an EPA official or your so called state regulators on a job site.

 

[Twowaxhack]

I just called Zurn and they claim they do not make any tank for flushing direct flushvalves.

It’s been done with a bladder tank (post #18) as I’ve explained earlier in the thread but Zurn laughed about it……

I talked to Diana in Tech support.

But hey, she could be wrong. Post a link to it

 

[Twowaxhack]

Great approach, especially since the issue will only raise its head when both toilets are flushing at the same time. A long at the flushes are not happening in a 5.5 second span, the flows and velocities will be well within design parameters.

Thanks Fishscreener!

Why would you design a system from scratch that doesn’t work ?


What brought me back to this thread is I worked at an office building last week.

I was called there to unclog the break room kitchen sink. I arrived right after lunch. I was filling the sink and a lady came out of the restroom and said “ I’m glad your here the toilet is running and it’s not stopping this time “.

I turned off the sink and asked her to go see if it stopped. It did.

I continued to fill the sink and the volume at the sink would take a nose dive and stay there……until I turned the sink off and then right back on.

Reason ? Because when I turned the sink off the line pressure would rise and the direct flushvalve would close.