DavidJ
Well-Known Member
My Seafire FM200 engine bay extinguisher is showing slightly overcharged. I note that the green bit assumes 70*F (21*C)
It’s now 31*C here. Could this account for the higher reading?
FM200 fire extinguisher overcharged
- Thread starter DavidJ
- Start date
My Seafire FM200 engine bay extinguisher is showing slightly overcharged. I note that the green bit assumes 70*F (21*C)
It’s now 31*C here. Could this account for the higher reading?
mcanderson
Well-Known Member
When a gas is trapped inside a container which has a fixed size (its volume cannot change) and the gas is heated, the particles will gain kinetic energy which will make them move faster.
The temperature of the gas is proportional to the average kinetic energy of its molecules. Faster moving particles will collide with the container walls more frequently and with greater force. This causes the force on the walls of the container to increase and so the pressure increases.
If the temperature of the gas is measured on the Kelvin scale, the pressure is proportional to the temperature.
From this we can derive the equation
\frac{P_{1}}{T_{1}} = \frac{P_{2}}{T_{2}}
The temperature of the gas is proportional to the average kinetic energy of its molecules. Faster moving particles will collide with the container walls more frequently and with greater force. This causes the force on the walls of the container to increase and so the pressure increases.
If the temperature of the gas is measured on the Kelvin scale, the pressure is proportional to the temperature.
From this we can derive the equation
\frac{P_{1}}{T_{1}} = \frac{P_{2}}{T_{2}}
Momac
Well-Known Member
Could this account for the higher reading?[/QUOTE]
Yes.
My Seafire extinguisher gauge shows a low reading in the winter, which is also normal.
Yes.
My Seafire extinguisher gauge shows a low reading in the winter, which is also normal.
DavidJ
Well-Known Member
Hi mcanderson I was hoping you would reply. I remember your earlier excellent accounts on this subject.
Can I trouble you to do the maths for me
240 psi at 21*C what is the pressure at 31*C
7.1 cu M capacity
4.95 Kg FM200
Can I trouble you to do the maths for me
240 psi at 21*C what is the pressure at 31*C
7.1 cu M capacity
4.95 Kg FM200
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mcanderson
Well-Known Member
Sorry you need to know the temp of the gas. I think it is simple enough to say that the higher temp has resulted in your gauge showing a higher reading and you can return to a normal state of being.
DavidJ
Well-Known Member
Many thanks
I will keep an eye on it when the ambient temperature returns to “normal” later in the year
If I assume the gas temp is the same as me at the moment ie 31 then I calculate the pressure to be 248 psi using p1v/t1=p2v/t2
Regards
David
I will keep an eye on it when the ambient temperature returns to “normal” later in the year
If I assume the gas temp is the same as me at the moment ie 31 then I calculate the pressure to be 248 psi using p1v/t1=p2v/t2
Regards
David
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rubberduck
Well-Known Member
Not far enough out to cause concern IMO
LittleSister
Well-Known Member
But in this case, isn't the gas in a container which will also expand in the heat, and hence increase the volume within it? Therefore the calculation of the pressure of the gas is, presumably, more complex.
DavidJ
Well-Known Member
With guys like mcanderson on here I feel on shaky ground but the volume is contained in the cylinder which is fixed. I discount any expansion of the cylinder which for 10 degrees is negligible
Lon nan Gruagach
Well-Known Member
Sure, but the expansion of steel over 10oC is really really tiny. Without delving into the specific steel used, its reasonable to use a linear coeficient of 11x10-6/oC so your extinguisher bottle might be about 1.00011 times a long and wide for a 10oC temperature rise.
superheat6k
Well-Known Member
Yes its pressure is rising due to the temperature.
However, no it is not overcharged, it is simply a refrigerant grade fluid (R227EA) with liquid and vapour both present sitting at its saturated pressure for its given temperature (for a static single component fluid in a sealed cylinder the liquid is at its boiling point and the gas above it is at its condensing point, but there is no bubbling, nor condensing, the fluid is simply stable).
The only danger arises when a cylinder is overcharged with liquid alone, no gas space above, leaving no expansion room in which case temperature expansion alone of a trapped liquid can cause an immense rise in pressure sufficient to burst a cylinder. Your simple gauge would be off the scale.
It will rarely see 31oC, but when it does its pressure will rise so this then enters the red zone on the very simple indicator gauge. But if you look closely at the gauge the overcharge zone begins at 130oF or 54.4oC when the bottle pressure will rise to 9.94 bar. These actual pressures are quite modest. At 31oC it is not that much higher than a typical cycle tyre ~4.5 bar. The discharge from your fridge will be getting up to 15 bar on a warm day.
The saturated pressure of FM200 AKA R227EA is ...
0oC 0.93 bar
10oC 1.78 bar
20oC. 2.89 bar
30oC 4.31 bar
31oC 4.47 bar
35oC. 5.14 bar
I would expect the cylinder you have there would have a burst pressure around 150 bar or probably higher. You are not getting anywhere close.
However, no it is not overcharged, it is simply a refrigerant grade fluid (R227EA) with liquid and vapour both present sitting at its saturated pressure for its given temperature (for a static single component fluid in a sealed cylinder the liquid is at its boiling point and the gas above it is at its condensing point, but there is no bubbling, nor condensing, the fluid is simply stable).
The only danger arises when a cylinder is overcharged with liquid alone, no gas space above, leaving no expansion room in which case temperature expansion alone of a trapped liquid can cause an immense rise in pressure sufficient to burst a cylinder. Your simple gauge would be off the scale.
It will rarely see 31oC, but when it does its pressure will rise so this then enters the red zone on the very simple indicator gauge. But if you look closely at the gauge the overcharge zone begins at 130oF or 54.4oC when the bottle pressure will rise to 9.94 bar. These actual pressures are quite modest. At 31oC it is not that much higher than a typical cycle tyre ~4.5 bar. The discharge from your fridge will be getting up to 15 bar on a warm day.
The saturated pressure of FM200 AKA R227EA is ...
0oC 0.93 bar
10oC 1.78 bar
20oC. 2.89 bar
30oC 4.31 bar
31oC 4.47 bar
35oC. 5.14 bar
I would expect the cylinder you have there would have a burst pressure around 150 bar or probably higher. You are not getting anywhere close.
DavidJ
Well-Known Member
Thanks superheat, most reassuring.
I was inspired to post this from one of your earlier explanations of overcharge problems which as I understood was critical for other mediums, not FM200.
I didn’t like to just ignore my gauge in case I hadn’t quite understood the chemistry/physics/mathematics.
Cheers
David
I was inspired to post this from one of your earlier explanations of overcharge problems which as I understood was critical for other mediums, not FM200.
I didn’t like to just ignore my gauge in case I hadn’t quite understood the chemistry/physics/mathematics.
Cheers
David