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[Jerry C]

Did anyone watch mythbusters tonight. Wow!
Jerry.

[essex2visuvesi]

bet you went and checked the safety valve on your hot water tank lol

Know I did when I saw that episode

[Jerry C]

Had one of that type in my last house and tested the safety whenever.  Have combi now. Thing was it didn't fail until 335 psi or there abouts. If I ran one at say 40 psi, how many tvr1as could I run on 3kW? Food for thought eh.
Jerry.

[Martin (Admin)]

 
That is a Great episode!  - http://youtu.be/rGWmONHipVo

[southsteyne2]

Wonder if ooyah watched it

[malcolmfrary]

A good quote from the comments section down the page on the link

We could ban everything that's even slightly dangerous and stupid people would still find ways to hurt themselves.

[giovanni]

Wow!
That is right next to my shop in Alameda, California!
I didn't realize that they were blowing up things that close to my shop.
They discharged a cannon ball at the Dublin, Ca. Shooting range and the cannon ball went ultra-ballistic and strayed off into a neighborhood and blew straight through a two-story house. The ball went through a wall, went up the staircase and punched through the upstairs wall, leaving a cartoonish perfect shaped round exit hole. Luckily no one was in the house. They got a lot of press over that stunt.

[Jerry C]

I, like a lot of peeps, try to think logically how the stunts on these programs will go. After seeing the small tank let go I was surprised that the pressure went as high as it did, so when they brought on the big one I thought it would fail at a lower pressure but I was wrong obviously. When fitting one I thought it was pretty flimsy, only rigid because of the outer skin over the lagging. Mine was a copper/stainless steel sandwich fitted with secondary heating coil and high and low level immersion heaters, thermostats, fusible link and fusible plug and a p/v valve with manual test/ reseat knob. It had a floating diaphragm between the surface of the water and the damping air above. As shown on the program you have to try quite hard to get one to explode and I would have no fears of having another. However maybe their strength is the problem. They are not required to boil water, no where near in fact. Perhaps making them weaker would make them safer?
Jerry.

[ooyah/2]

Wonder if ooyah watched it

No John, not this time but I have it on record from some months ago.

No doubt you will have noticed that they deliberately stopped off the safety valve which I have never ,nor will ever advocate on this or any other forum that anybody should do this and then steam up a boiler..

If you disagree with anybodies comments or advice may I suggest that you say so, which can lead to an open discussion and hopefully arrive at the correct conclusion rather than making snide and sarcastic comments as you have to date and in the past.

George.

[steamboatmodel]

As George said they disabled all the safeties, which probably not only mean the safety valve but the fusible plug as well.
Personally I think that these type of videos show extremely irresponsible behavior and quite often give the wrong impression on things. When this was first shown it was being discussed at the local coffee shop, and the majority of the people who had watched it did not remember them saying that they had disabled the safeties and said that they had used normal water heaters. There were even some salespersons’ going door to door selling instant heat water heaters installation and referring to the show to frighten people into buying. This was stopped when the local gas and electric suppliers laid charges and threatened to sue.
Regards,
Gerald.

[Jerry C]

Somebody, somewhere did something stupid to his water heater and it went bang and took off through the roof. Was it a myth or did it really happen.
             The program showed that it could happen. It also showed people how bad it could be. How many peeps tried there safety valves as essex2vusuvela suggested. I did and I've only got a combi, just serviced.
  I don't see it as irresponsible programming.  If I can learn something from it so can others. There will always be some peeps beyond help.
Jerry.

[Umi_Ryuzuki]

At the end of this segment, the host, Adam, says,

"if someone sees water dripping from that pipe coming off the top of the water
heater, that doesn't go anywhere,  I hope they don't think Oh, maybe I should cap that.

http://www.youtube.com/watch?v=jbreKn4PoAc

two story test...
http://www.youtube.com/watch?v=9bU-I2ZiML0

[gondolier88]

What a stupid and inane 'test'- to measure the max. pressure loading of a water heater while it's cold proves nothing except what any design engineer could have told you- the tensile strength of the materials and the joint failure pressure of the vessel.

The danger in any water heater/boiler is the combination of heat and pressure- that last test, if it had been at 100+deg.C, would more than likely have blown their blast shelter into the cabin behind, assuming it got to the same pressure as the cold test- which is highly unlikely.

It also goes to show exactly what a cold hydro test on a steam boiler is for- joint testing only. A live steam test is the only way to prove a boiler is safe.

If anyone takes the time to go and examine a safety valve on an unvented hot water cylinder (which is what mythbusters are 'testing') they will see it is rated as a 'combined pressure and temperature release valve'- in other words it governs not only pressure (of little consequence in reality- something that 'test' did prove), but also the heat of the cylinder- EU rules stipulate never more than 95deg.C by the way.

Anyone who is now worrying about their combi' blowing up- don't! The pressurised side of a combi' is central heating only, it has a pressure release valve only, set to between 2.5 and 3 bar. To govern heat it has a heat exchanger over limit thermostat (cuts gas and shuts boiler down if a temperature of over 95deg.C is reached), it also has a flow sensor that if it doesn't sense a flow through the pipe (ie. pump failure) will shut the gas valve down, it also has a pipe stat' on the return that governs how much the burner is on, which if it fails will shut the gas valve.

Don't go testing your safety valve on your central heating unless you know how to replace it yourself and know how to re-pressurize your heating. The amount of heating systems that constantly need topping up because someone has decided to 'test' the safety valve is unbelievable- they are simply an O-ring on a seat held by a stainless spring- I've NEVER known one to fail unsafe yet, but I've known plenty that have leaked forever more because when it was 'tested' the O-ring split/grit got stuck on the seat/spring broke- they are a once only item, if yours is running get a gas engineer to come and find out why, and then replace it.

Greg

[essex2visuvesi]

made for good TV tho

[malcolmfrary]

Stupid and inane it may have been, but that is basically the point of the show.
Was it a cold test?  Not really, from what I recall of the series, the method was to seal all of the inlets and outlets while disabling the safety features to make sure that the limit was reached, then switch on the heating element of the full tank and leave it running, so it was full of very hot water ready to turn into lots of steam when the opportunity arose.  The pressure was thus derived from the heating of the water. 
The fact that many of the audience reached their various conclusions independently of any of the other information given in the show (rather than just the clip), such as the method, the reasoning behind the method and what the original myth actually was, says more about the audience than the show itself, and this is true for many of the myths tested.

[Jerry C]

That's what I thought but didn't have access to see the full show again. I do remember seeing them removing a thermostat from an immersion heater element and on the clip after the event they used the word steam.
As I understand it a cold, hydraulic test with no air in the system would never be explosive or dangerous (that is why  we do it that way) no energy being stored.
I forget how much a volume of water becomes when it turns to steam and allowed to expand but in the show they mentioned this. If it was a hot test the temp of the water at  330psi was also mentioned in deg F.
I have watched the clip a few times and see each time a lot of water but not as I expect a very large volume of steam. What is the factor for water to steam?
On the subject of testing relief v/v's on unvented tanks, I'm reasonably sure mine had a big notice on the tank telling me to regularly lift the latch and observe the tunndish was clear. Never had a problem with my combi being tested and very easy to top up.  One click doesn't drop the system pressure noticeably.
Working on the principle that if something can go wrong it invariably will and due to the fact that I have seen many malfunctions of p/v valves on VLCC s I test my combo relief valve when I remember. Better a leaky valve than leak in the system. The boiler is nearing its end at 15 years and in that time it's only required a new auto air valve and an expansion tank due to diaphragm failure.
Jerry.

[Jerry C]

  I knew I'd read it somewhere. This found on combi_boiler.net ;
Safety valves – The combi boiler safety valve is the most important valve on the boiler. Safety valves prevent dangerous over pressurization of the boiler. Safety valves are installed in case there is failure of pressure controls or other devices designed to control the firing rate.
 All safety valves should be kept free of debris by testing the safety valve regularly. This should be done when the pressure is at approximately 75 percent of the safety-valve set pressure. Safety and safety-relief valves on low-pressure boilers should be tested at least quarterly, this is in accordance with the National Board Inspection Code.
Jerry.

[gondolier88]

Stupid and inane it may have been, but that is basically the point of the show.
Was it a cold test?  Not really, from what I recall of the series, the method was to seal all of the inlets and outlets while disabling the safety features to make sure that the limit was reached, then switch on the heating element of the full tank and leave it running, so it was full of very hot water ready to turn into lots of steam when the opportunity arose.  The pressure was thus derived from the heating of the water. 
The fact that many of the audience reached their various conclusions independently of any of the other information given in the show (rather than just the clip), such as the method, the reasoning behind the method and what the original myth actually was, says more about the audience than the show itself, and this is true for many of the myths tested.

Have a look at video link Martin posted- go to frame 1:10- pressure reads 258psi at 76deg.F, or 24.4deg.C.

That's what I thought but didn't have access to see the full show again. I do remember seeing them removing a thermostat from an immersion heater element and on the clip after the event they used the word steam.
As I understand it a cold, hydraulic test with no air in the system would never be explosive or dangerous (that is why  we do it that way) no energy being stored.
I forget how much a volume of water becomes when it turns to steam and allowed to expand but in the show they mentioned this. If it was a hot test the temp of the water at  330psi was also mentioned in deg F.
I have watched the clip a few times and see each time a lot of water but not as I expect a very large volume of steam. What is the factor for water to steam?
On the subject of testing relief v/v's on unvented tanks, I'm reasonably sure mine had a big notice on the tank telling me to regularly lift the latch and observe the tunndish was clear. Never had a problem with my combi being tested and very easy to top up.  One click doesn't drop the system pressure noticeably.
Working on the principle that if something can go wrong it invariably will and due to the fact that I have seen many malfunctions of p/v valves on VLCC s I test my combo relief valve when I remember. Better a leaky valve than leak in the system. The boiler is nearing its end at 15 years and in that time it's only required a new auto air valve and an expansion tank due to diaphragm failure.
Jerry.

Jerry,

Water flashes into steam at any pressure when 100+deg.C, it expands at a ratio of 1600:1, so the 52gal cylinder would become 83,200gal steam (by volume). Just to be clear- on an unvented HW cylinder it is the mains water that is held at a pressure and temperature in excess of supply.

  I knew I'd read it somewhere. This found on combi_boiler.net ;
Safety valves – The combi boiler safety valve is the most important valve on the boiler. Safety valves prevent dangerous over pressurization of the boiler. Safety valves are installed in case there is failure of pressure controls or other devices designed to control the firing rate.
 All safety valves should be kept free of debris by testing the safety valve regularly. This should be done when the pressure is at approximately 75 percent of the safety-valve set pressure. Safety and safety-relief valves on low-pressure boilers should be tested at least quarterly, this is in accordance with the National Board Inspection Code.
Jerry.

I didn't say don't test SV's on unvented cylinders- this is a good idea. I said it isn't a good idea to test combi' boiler PRV's- for the very reason the site you mention says you should do it- 'kept free of debris'!! The valve doesn't get blocked by debris, it will, however, get blocked open by debris. Not only that, but that is a US site, who's to say they have the same EU standard design PRV's on their boilers? It isn't dangerous, or even silly to test it, but it is unnecessary and you risk doing damage to the valve and losing your central heating until it's fixed.

Greg

[Jerry C]

I think I'd better bow out of this one.
Jerry.

[southsteyne2]

If you disagree with anybodies comments or advice may I suggest that you say so, which can lead to an open discussion and hopefully arrive at the correct conclusion rather than making snide and sarcastic comments as you have to date and in the past.






Sorry George as it seems we agree to disagree as my post was not meant to be sarcastic merely a recall on  your statement that boilers do not explode and also my comments and others were virtually shot down in flames and as for being sarcastic, your comment that some people post what they read in books may be true but not all of us so for me there will be no further comments on boilers on this forum
John

[derekwarner]

southsteyne2 .....you must realise that forums such as Mayhem have a broad & diverse range of members from different educational & engineering backgrounds

You will have noticed examples by very talented builders be they be vessels or engines, however I feel very few indeed would be fully self taught  .......so for my money if you don't have a talented trainer...the next best thing is education and if that includes reading books then so be it

The important thing is to never bring yourself down to the silly sarcastic  level of others.........Derek 

[ooyah/2]

If you disagree with anybodies comments or advice may I suggest that you say so, which can lead to an open discussion and hopefully arrive at the correct conclusion rather than making snide and sarcastic comments as you have to date and in the past.






Sorry George as it seems we agree to disagree as my post was not meant to be sarcastic merely a recall on  your statement that boilers do not explode and also my comments and others were virtually shot down in flames and as for being sarcastic, your comment that some people post what they read in books may be true but not all of us so for me there will be no further comments on boilers on this forum
John

John,
I accept what you say that you didn't intend to be sarcastic, however from my side of the fence it sure read as such, as it would appear to be the same as the other members who shot you down in flames.
This being an open forum,  members will give an opinion and advice, if you thinks it's wrong why not say so and let it be discussed in an open and friendly manner that we can all benefit from.

For instance, Derek and I have not always agreed but I would like to think that we are open to discuss differences and at the end of the day don't take the hump, his use of funny faces gets right up my nose to which I have told him so but it's his prerogative to use them if he wishes too.

Don't disappear lets hear your views on boiler construction and uses, life is to short to grumble but if you no longer wish to comment on the subject that's' up to you.
George.

[derekwarner]

Gents........could I suggest a Moderator reviews this thread & make a call to LOCK the thread

1. Since posting No2 on 21st August.......the response/comments have deviated from the original subject
2. As usual......certain members comments & opinions seem to infuriate   other [certain] members
3. Some members appear to continue to offer bigoted remarks of their own view/s by their posted comments  
4. I have intentionally not commented in this original subject matter [Exploding hot water heater] as I considered that it had little relevance to our model boiler examples
5. I acknowledge that I did not have a talented personal teacher.....  so yes I reverted to reading engineering articles
6. When I have posted technical comments to questions raised by others ...I have always acknowledged the text source if applicable

Derek

[Martin (Admin)]

Please keep comments civil and we'll be aright.  



Tell me, does it make any difference if you have a sealed vessel filled with water (no air at all), and then you heat it up?

[ooyah/2]

Martin,
This is how a hydraulic test can be  done on a pressure vessel, as you heat the water it expands and if a joint gives way in the vessel it will pump out the water but as it's not up to a very high temp all that would happen is that you would get a shower of warm water.

The big problem is that if a pressure gauge isn't fitted by heating the vessel you can go way beyond it's design criteria, it's once that you get beyond that the trouble starts and the vessel could rupture with serious consequences.

In the Myth busters in their first experiment the filled the tank,  which duly burst but not so spectacular, in the final try they half filled the tank  and when it reached 360 C  and the bottom came off the tank the steam and the water immediately when it hit atmosphere expanded 1600 times hence the massive explosion.
Just shows the power of steam.
George.