# Water heaters and vacuum relief and anti siphon valve/s



## ECH

Can someone help me understand the function and application of these devices?

I helped with an "apollo" (side loop for the HVAC) style heater and it failed inspection due to not having a vacuum relief valve on the side loop inlet (lower).

Heater was located on first floor laundry closet of 2 story condo, city water, prv, etc.

It's my understanding that the vacuum relief valve prevents back siphonage if the main is shut off and somebody tries to run water, but the domestic side of the heater is protected by the holes in the top of the dip tube, and the side loop has the circ pump for the air handler, but it returns the water back to the heater, so net pressure/vacuum is zero, so how would siphonage occur?


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## MACPLUMB777

The Most Important (3) Letters to "REMEMBER" IS A.H.J
BETTER KNOWN AS AUTHORITY HAVING JURISDICTION ! :biggrin:
They are the one's who decide what is right in your area,


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## ECH

10-4


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## Alan

It should also prevent a vacuum on the tank that would cause it to implode on itself. Marathon heaters come with them installed on the tank.

I've seen this on extreme situations in well systems where the pressure tank is an extremely large distance above the well. Pump check valve fails, water tries to flow back with nowhere to get air from and tank implodes. 

That was many years ago. Should have grabbed a picture of it.


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## Master Mark

Alan said:


> It should also prevent a vacuum on the tank that would cause it to implode on itself. Marathon heaters come with them installed on the tank.
> 
> I've seen this on extreme situations in well systems where the pressure tank is an extremely large distance above the well. Pump check valve fails, water tries to flow back with nowhere to get air from and tank implodes.
> 
> That was many years ago. Should have grabbed a picture of it.




This topic is a total joke....imploding water heaters are rare or almost impossible to find..

of course if the local plumbing inspectors insist on having one on the heater then you are gonna haave to install one.... Basically they are just something that will leak sometime down the road and probably cause damage

if you actually run into a water heater that has imploded I would like to see pictures of it..... that is like finding a purple unicorn or bigfoot....

looking on google you can find a lot of heaters that have blown up but I have yet to see one that has sucked into itself.... it just dont happen:devil3::devil3:


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## ShtRnsdownhill

Master Mark said:


> This topic is a total joke....imploding water heaters are rare or almost impossible to find..
> 
> of course if the local plumbing inspectors insist on having one on the heater then you are gonna haave to install one.... Basically they are just something that will leak sometime down the road and probably cause damage
> 
> if you actually run into a water heater that has imploded I would like to see pictures of it..... that is like finding a purple unicorn or bigfoot....
> 
> looking on google you can find a lot of heaters that have blown up but I have yet to see one that has sucked into itself.... it just dont happen:devil3::devil3:


 well....take a good look at this link....
https://www.google.com/url?sa=t&rct...erly-vented/&usg=AOvVaw0VCUwHzo6Uif9tDrZ71C6g


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## Alan

North of me where I used to work, we have a lot of really low pressure systems that are up high on hilltops. Fire department has drained the system before using hydrants down at the bottom.

You're right, they are rare. I haven't seen a water heater do that, but I suppose just like all of the other hypothetical situations in our codes, it COULD happen. :biggrin:


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## ShtRnsdownhill




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## ShtRnsdownhill

this helps explain it..


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## ECH

Ok, I understand the concept, but if that's the case why aren't we being required to put one on every WH?

A.H.J. lol.


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## ShtRnsdownhill

ECH said:


> Ok, I understand the concept, but if that's the case why aren't we being required to put one on every WH?
> 
> A.H.J. lol.



proper use of a water heater is its usually full of water and water doesnt compress, so the only chance a water heater may implode is if its empty with a suction, which is almost impossible, most codes and safety devices come around because of instances in the past and imploding water heaters is as rare as seeing a dodo bird nowadays..oil tanks in the basement have imploded if the right conditions occur, but only when not full..


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## skoronesa

One are we work in requires vacuum breakers on the water heater. We were told by the inspector that this is so the tank is siphoned out allowing the elements to turn the rest into steam and either make dangerous pressure if a valve is shut or so that the elements dont burn out.

I have never heard of a waterheater imploding but I guess youre right, bad check valve in a submersible pump with a static level 300' down and a power outage could easily pull -80psi.


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## Master Mark

ShtRnsdownhill said:


> proper use of a water heater is its usually full of water and water doesnt compress, so the only chance a water heater may implode is if its empty with a suction, which is almost impossible, most codes and safety devices come around because of instances in the past and imploding water heaters is as rare as seeing a dodo bird nowadays..oil tanks in the basement have imploded if the right conditions occur, but only when not full..



You have a better chance of seeing big foot... Water heater dip tubes have an anti siphon hole in them that keeps this thing from ever happenning


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## ShtRnsdownhill

Master Mark said:


> You have a better chance of seeing big foot... Water heater dip tubes have an anti siphon hole in them that keeps this thing from ever happenning



I was close by saying a do do bird....:biggrin:


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## 89plumbum

ShtRnsdownhill said:


> I was close by saying a do do bird....:biggrin:


How about the Tasmanian Tiger?


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## ShtRnsdownhill




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## ECH

The holes in the dip tube will prevent siphoning of the water as soon as the water level gets below the holes, but will still allow a vacuum to form in the tank. Hence, the spirit of the requirement (my understanding anyway).

Somebody would have to drain it, then put a pump on it and let er pump for a while. It "could" happen couldn't it?

(assuming, the main and faucets are closed of course.)


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## Master Mark

ECH said:


> The holes in the dip tube will prevent siphoning of the water as soon as the water level gets below the holes, but will still allow a vacuum to form in the tank. Hence, the spirit of the requirement (my understanding anyway).
> 
> Somebody would have to drain it, then put a pump on it and let er pump for a while. It "could" happen couldn't it?
> 
> (assuming, the main and faucets are closed of course.)



Ducks could come flying out of my ass too or maybe monkeys.. 


quack


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