repair leaking pressure release valve on 8r hunter

my 8r hunter stove emits out flames every now and again on my filler cap valve.

this would probably explain why my flame from the burner is not as good as it used to be either.

i cant locate any spares, and they are quite expensive, somwhere here was an article on repairing them, telling you to amke a pentagonal key to unscrew the valve.

anyway, it would be quite simple to fix i would imagine, its just a rubber diaphragm and a spring, i just wanted to see the photos.

Note, this is not the midi pump cap i am talking about here.

thanks for your help.

 

What is the actual need for the safety release
valve in the cap in the first place ??

I realize that the safety folks would say that this
prevents elevated pressure in the fuel tank.

Should there be elevated pressure in the tank, I
would assume that this would increase the rate of
burning, giving a larger flame and lowering the pressure.

As such, I once again question the need for the safety
mechanism in the tank cap.

Also, if one would insist on having a safety release device,
why locate it so it is pointed at the operator of the stove.

Just my thoughts. I say get rid of the safety device.

Ken H.

 

My instinct tells me that there is a limit to how much fuel can flow through the jet at a given moment, no matter what the pressure behind the fuel is. Increasing the pressure won't increase the fuel flow rate, once the maximum rate is achieved.

If the pressure continues to increase

But I could be wrong, I usually am.

 

I think you're right spudz.
An orifice works (within certain limits) as a basic flow regulator, so it'll only flow up to a certain volume (or at least it becomes heavily non-linear once you pass its 'sweet spot').

Hence, if you don't have the pressure release in the cap, you could experience a tank rupture if the pressure / heat climbed too high.

Although the in-cap regulators are very simple devices (I saw the same 'how-to' article on here once, but can't find it now!) and well within the abilities of most people who fettle stoves to dismantle, I'm not sure how you'd set the relief pressure when you reassembled it.

It's just set by varying the preload on a small spring via the pent screw in the cap, but without test gear, you'd be guessing?.....

best
Matt

 

I think spudz is right. the question is even if you had the right pentagonal key to open up the release valve, remove the spring and (presumably) replace the faulty seal... How would you know the right amount of tension to place on the mechanism when tightening back down? You would need to know the number of atmospheres the 8r tank is capable of taking and then scale back slightly to give yourself a safety margin. You would need some sort of bench to test the cap. It seems that the cheaper easier thing would be to just buy a new cap from a&h.

I had the cap blow on my 111 while it was running and so the higher output thing is not true. To answer the question on why the release is facing the operator, just operate the stove from the side. In operation, all you really need is access to the adjustor valve.

 

I think the reason it points where it does is because it'd vent hot petrol vapour and it's preferable to have it pointing away from the big flamey hot bit at the other side of the tank!

Matt

 

it doesn't take that long for gasoline vapors to cover that distance... even if pointed in the other direction

 

True enough but at least it gives you the best chance of avoiding a flamethrower / BLEVE type event

best

Matt

 

O K here is what i found out a new cap pressure valve is set at 80 p.s.i.. I made a jig so i can test mine . For what is worth a 123 when burning only builds up between 5 & 10 p.s.i. on a hot day 15 to 20 psi. don't repair less you can test them like i can be safe. i also did a pressure check on 8r and 111 but forgot on them

 

An orifice works (within certain limits) as a basic flow regulator,
so it'll only flow up to a certain volume (or at least it becomes heavily
non-linear once you pass its 'sweet spot').



As I understand it, fluid flow thru a nozzle is related to the driving pressure.

When the pressure increases, the rate of flow increases, to a point.

At this point of elevated pressure, the fluid flow approaches the speed of sound
and no matter how much the pressure is increased, the rate of flow stays essentially the same.

Should you be operating at this point, an explosion is imminent.

But I question how close to this point do these stoves operate ?

Ken H.

 

i dont think saftey is too much concern, as it is a self pressurised tank, and does not build up much pressure, as it has no pump, the pressure would be far more using the midi pump itself, as long as the valve is not letting out the pressure from the tank, i think there is far more of a risk of an explosion if there is a flame coming out of the filler valve, id say the rubber seal is tired more than anything.

 

I am not at all certain that on a self pressurizing stove a safety mechanism
is of any value, nor do I think it is any asset.

IMHO, we would be better off without them.

Coleman and others recognized this from the start.


Ken H.

 

I think you will find that Coleman do not solder their tanks maybe why no relive valve

 

i dont think any of the optimus 8r, 22, 111 stoves were soldered, my tank appears to be either silphos, or braised, as it looks similer to brass on the join

 

As a case in point, when we teach the operation of the 8R, we make a point of emphasising to always operate the stove with the key facing the operator, and the cap / tank pointed at 90 degrees to the side. This does not remove, but reduces the risk of operator injury in case of an over-pressure event. Regards, Rob

 

I think a new cap is in order. I'd hesitate to second guess the factory on safety matters.

The 123 uses the same cap and burner and has a nickname: "The Swedish Hand Grenade." That name is well earned.

Few things are as exciting as a gasoline explosion when one least expects it. Or as hard on one's undies (knickers) and pride.

My 2 cents.

Gerry

 

Never seemed to have any trouble with my lot of these burners yet.
But how common it the hand grenade saga??

Seems if it starts to really hummm long before the whistle and boom a simmer is still full blast then I would turn it off or pour water on it before the immanent happens.

DO I turn on flat out with a tight windscreen big pot and go for a walk for 1/2 an hr or what??

How do you get to thrown the now red hot brass grenade without 3rd degree burns to your hand??
Or do I just use me steel caps.
How does that help beside burning more area and creating the perfect final condition to bleve-dom.




Barra

 

How come i am the only one that test these things. A new cap test out at 80 psi. the 123 when burning gets only 20 psi in tank and the fuel temp was 120F. beleve it or not

 

Probably one of the few that has a rig to test them OOPS
Rest of us only got one or two maybe an just too lazy to knock something up


barra

 

Yep got time plus in my blood been making things and testing all my life.Plus where i use to work always made new parts for the machine at work. Most of the time if i can see it can make it or better.Many years ago took a lawn mower made a welder out of it light work.