Hot Water Tank "Implosion"?

RickDelta

Hello HeatingHelp.com community!

I have a commercial (motel) customer with a three story building (no basement) and a small roof top boiler room (fourth story) with four 120 gallon hot water tanks.
2" cold street supply vertical up to the boiler room, heated, then 2" hot down to 1st floor ceiling to a "T" branch pattern pipe distribution, where all three floors of the guest rooms are serviced from.

The system was not designed with any "vacuum breakers". My concern is should the main cold IN flow pipe break at street level (interior side of the back-flow preventer) I could develop a backwards flow siphon creating a vacuum tank collapse.

I'm assuming this doesn't happen in a typical two story residential home where the hot water tank is in the basement or 1st floor level and a sufficient siphon can't be generated.

Is this a valid concern here?

Thanks!

EBEBRATT-Ed

That is why some states require vacuum breakers. Some do not. MA does Ct does not

RickDelta

........ not a concern then?

Jamie Hall

RickDelta said:

........ not a concern then?

Very much a concern. The fact that one state requires them and another doesn't (it's a wonder the two @EBEBRATT-Ed mentioned agree on the time of day) is irrelevant. It's just good practice to have vacuum breakers in that scenario.

psb75

I agree with Jamie, especially because of this: 4 roof-top (4th story) 120 gal. tanks.

RickDelta

So .... lets say I shut off the water main where it comes in at ground level.
I go outside and open the hose bib to drain down the system.

I could actually collapse the four tanks on the roof?? : (

These hot water heater/tanks are $12K each!! : (

RickDelta

..... I wouldn't want 480 gallons of hot water sitting over my 60 newly remodeled guest rooms! : (

...... I forgot they also have just a plain "storage only" tank, 120 gallons (no heat) in front of the tanks pictured here. : (

600 gallons total!!

hot_rod

Vacuum relief valve requirements have been in the plumbing codebooks for years. Here is a 2015 version of the UPC.
It depends on what code and what year code book is used in your area. If any??
Also if the inspectors even know what the valve does, what it looks like, and if it is properly installed.

Regardless, common sense also dictates when you should insist on having this protection.

Caleffi addd them to out offering recently and we are shipping pallet loads of them to wholesalers. So perhaps they are becoming more applied. As well they should be

leonz

Does this municipal cold water delivery system even have a back flow preventer after the water meter???

I guess they were not interested in pumping hot water from the ground floor on demand as may hotels do using small circulators with basement placed hot water boilers???

ChrisJ

@Larry Weingarten. 

Intplm.

It can't hurt to install them. Install one on each tank.
It looks like a very nice set up. Install them for what they are designed to do. This situation truly warrants it.

RickDelta

@leonz

Does this municipal cold water delivery system even have a back flow preventer after the water meter???
Yes! ..... one big main off the street (8"), then splits into fire sprinkler and cold water feed for building.



..... does anyone have an answer for this below?

So .... lets say I shut off the water main where it comes in at ground level.
I go outside and open the hose bib to drain down the system.

I could actually collapse the four tanks on the roof?? : (

pecmsg

RickDelta said:

@leonz Does this municipal cold water delivery system even have a back flow preventer after the water meter??? Yes! ..... one big main off the street (8"), then splits into fire sprinkler and cold water feed for building. ..... does anyone have an answer for this below? So .... let’s say I shut off the water main where it comes in at ground level. I go outside and open the hose bib to drain down the system. I could actually collapse the four tanks on the roof?? : (

Impossible to answer

RickDelta

I'm familiar with the commercial flat roof "siphonic" rain water drain systems.

The roof drain inlets don't allow air to be ingested with the standing rain water, the horizontal and vertical down piping contains only 100% filled rain water.
This creates an enormous and continuous hydraulic suction slug of water from the roof inlet all the way out to the street level discharge. (you actually have to slow the escape velocity down or it would shoot out like 30 feet!!)

I'm assuming these are the same downward, gravity feed hydraulic pressures created in my tank implosion question above.

If the siphonic pressures create a vacuum greater than the tanks crush design ..... the tank ruptures.

Larry Weingarten

Hi @RickDelta , If you're feeling brave, you could get a vacuum gauge and put it on one of the tanks, then do your test of shutting off water and opening a drain valve at ground level. I might do it if I has someone up at the tank reading the gauge for me. But for really rough numbers, think of a forty foot elevation... or a water column that could create around minus 20 psi. A 120 gallon tank has about 5400 square inches of surface area.That times 20 pounds means a compressive force of about 54 tons on that tank! I'm really liking the idea of a vacuum breaker or two!

Yours, Larry

RickDelta

..... thinking:

A high end motel like this would have had vacuum breakers installed on the originally installed tanks when the building was brand new (as code would demand .... PA Code?)
Over the years as these tanks were replaced ...... the vacuum breakers were overlooked? : (

leonz

If your going to shut the water off at the street you need to open every hot and cold water tap in the building from the roof boiler room down, shut off the power and gas to the water heaters, open the water heater drains and leave them open to let the entire water system drain out otherwise all the water will not be drained out.

If you want to have some fun look up railway tank car implosions on you tube.

When railroad tank cars are steam cleaned internally and the cleaner makes the mistake of closing the tank car hatch sealing the tank car lid gasket BEFORE closing the center bottom drain valve when he climbs out the tank car it begins to cool and as a result the tank car collapses with the change in air temperature.

What you are referring to is atmosperic pressure differential in roof mounted gravity rainwater drains.
Properly designed roof drains and scupper drains allow water to fall away quickly with no resistance to the street gutters.

Roof drains on flat roofs only have one atmosphere of pressure in them WHEN PROPERLY SIZED.

If the roof drain piping is improperly sized and installed up and over other piping rather than under it and then back to continue to drain it does not have the benefit of gravity and the high point will need a pipe U fitting with a plug to break the vacuum as the water in the pipe will become stagnant.

Simple gravity is allowing the water to drop and atmospheric air pressure is replacing it from the bottom up if you have roof drain water flows like this.

The roof drains in the system you are describing must have debris plugging it as the rain water should drop away with no resistance to flow UNLESS they designed it with smaller drains and installed it wrong.

RickDelta

"@Leon"
If your going to shut the water off at the street you need to open every hot and cold water tap in the building from the roof boiler room down and leave them open to let the entire water system drain out otherwise all the water will not be drained out.

My intention is NOT to"drain the system down"

.....My thoughts:


Lets start with system at idle (NO water demand anywhere).
Water PSI in all pipes = 80 psi.
Now, street main valve is turned off at ground level.
No problem here.

Now, go outside and quickly open hose bib full open (emulating a pipe break).
The once "static" 80 psi ..... now becomes a violent 80 psi burst back-flow spike!
As this reverse high pressure downward spike of water escapes out the open pipe, NOT having any water or air to replace its volume, It creates a dangerous dynamic (gravity + 80 PSI) siphon and internal vacuum within the tank to the point of collapse.

........ not sure of any of this (i'm not a plumber) : )

RickDelta

leonz said:

If your going to shut the water off at the street you need to open every hot and cold water tap in the building from the roof boiler room down, shut off the power and gas to the water heaters, open the water heater drains and leave them open to let the entire water system drain out otherwise all the water will not be drained out.

If you want to have some fun look up railway tank car implosions on you tube.

When railroad tank cars are steam cleaned internally and the cleaner makes the mistake of closing the tank car hatch sealing the tank car lid gasket BEFORE closing the center bottom drain valve when he climbs out the tank car it begins to cool and as a result the tank car collapses with the change in air temperature.

What you are referring to is atmosperic pressure differential in roof mounted gravity rainwater drains.
Properly designed roof drains and scupper drains allow water to fall away quickly with no resistance to the street gutters.

Roof drains on flat roofs only have one atmosphere of pressure in them WHEN PROPERLY SIZED.

If the roof drain piping is improperly sized and installed up and over other piping rather than under it and then back to continue to drain it does not have the benefit of gravity and the high point will need a pipe U fitting with a plug to break the vacuum as the water in the pipe will become stagnant.

Simple gravity is allowing the water to drop and atmospheric air pressure is replacing it from the bottom up if you have roof drain water flows like this.

The roof drains in the system you are describing must have debris plugging it as the rain water should drop away with no resistance to flow UNLESS they designed it with smaller drains and installed it wrong.

hot_rod

It may be one of the least expensive safety devices you can buy for plumbing systems. Cheap insurance IMO

RickDelta

Thanks everyone!

I leave with, If the tank is above the outlet fixtures or feed supply, always install a vacuum breaker to prevent possible siphonic vacuum tank rupture.

RickDelta

"@Larry Weingarten"

Hi @RickDelta , If you're feeling brave, you could get a vacuum gauge and put it on one of the tanks, then do your test of shutting off water and opening a drain valve at ground level.

..... I'm brave enough! : )
..... just not rich enough! : (

The tanks are $12K each!