Stirring a hornets nest
Discussion
Thats how my caps are installed and it all works perfectly. As it says ensure that the seal on the swirl pot cap is in good nick, if its missing like mine was just use a bit of old inner tube rubber to make one. Now when its hot the water raises in the expansion bottle to approx half way and when it cools it drops to approx the level sensor.
Engine temp sits solid no matter if i am stuck in traffic or running around.
Pete
Engine temp sits solid no matter if i am stuck in traffic or running around.
Pete
Sean,
Thanks alot for the above, but IMO what it shows is that TVR didn't really know what they were doing and kept changing their minds. My caps are the other way around and it works equally as well as the post above this one. As an Engineer who works with fluid systems I can say that both should work euqally well, but the pressure the cooling system runs at will vary bewteen the two. I'll attempt to explain why below noting that both methods have advantages and disadvantages.
Firstly however the TVR statement about the plastic bottle splitting is B
s to say the least. This is from a donor car and most cars cooling systems operate at 0.8b (10ish psi) or 1.1b(15psi) and as such the bottle will be designed to take up to twice this pressure, so even in the worst case scenario should take at least 1.6b.
Caps as per TVR dit above:
Advantages:
Cooling system runs at 1.1b therefore less susceptible to cavitation and wear at water pump.
Higher pressure system is more efficient (very slight though)
Disadvantages:
More prone to hose leaks (higher pressure and pulsing)
More prone to failure of pressure cap relief system (these caps are designed to relieve when needed and not control a flow of water to/from the expansion bottle)
If cap fails there is no system over pressure protection (until a hose/radiator splits)
In the above case the system works as described by TVR with the system operating at 1.1 bar. It is imperative in this case though that the swirl pot cap is very well sealed and that the expansion vessel is free to vent. If not you will end up with a leak at the swirl pot or a vacuum drawn on cooling down respectively. Note that as the water expands and the the pressure cap relieves to the expansion chamber the nature of the "solid" system will result in sudden depressurisations of the system and then a steady pressure increase again, which will pulse the pressure.
Other way around.
Advantages
reverse of disadvantages above.
Plastic bottle acts a second "potential over pressure protection device"
Relief cap only relieves when pressure is excessive
Disadvantages:
Reverse of advantages of above
In this case the swirl cap cover (non pressure) must be well sealed and the pressure relief cap must also be well sealed to the expansion bottle.
In this mode the system will run at a lower pressure (probably around 0.8b judging by the water level changes in my expansion bottle from hot to cold) and as the water warms up the expanding water freeflows to the expansion bottle compressing the air at the top and slowly compressed the air building up a slight overpressure. As the air acts as an accumulator the system is not "solid" and as such pressure changes are mild in comparison to the mode of operation above.
As I started off saying it appears even TVR couldn't make up their mind and who's to say they didn't release a third tech memo reversing the second one again!!! But from a purely engineering fluid dynamic perspective either should work and it is really personal preference as to whether you want a solid system running at 15psi or a system with an accumulator running at a lower pressure. I personnally prefer the latter. BUT IN BOTH CASES YOU MUST MAKE SURE THE CAPS ARE SEALED OR VENTED AS STATED ABOVE FOR THE APPROPRIATE CONFIGURATION - THIS IS KEY IF YOU DON'T WANT TO BREAK ANYTHING
Mark
Thanks alot for the above, but IMO what it shows is that TVR didn't really know what they were doing and kept changing their minds. My caps are the other way around and it works equally as well as the post above this one. As an Engineer who works with fluid systems I can say that both should work euqally well, but the pressure the cooling system runs at will vary bewteen the two. I'll attempt to explain why below noting that both methods have advantages and disadvantages.
Firstly however the TVR statement about the plastic bottle splitting is B
s to say the least. This is from a donor car and most cars cooling systems operate at 0.8b (10ish psi) or 1.1b(15psi) and as such the bottle will be designed to take up to twice this pressure, so even in the worst case scenario should take at least 1.6b.Caps as per TVR dit above:
Advantages:
Cooling system runs at 1.1b therefore less susceptible to cavitation and wear at water pump.
Higher pressure system is more efficient (very slight though)
Disadvantages:
More prone to hose leaks (higher pressure and pulsing)
More prone to failure of pressure cap relief system (these caps are designed to relieve when needed and not control a flow of water to/from the expansion bottle)
If cap fails there is no system over pressure protection (until a hose/radiator splits)
In the above case the system works as described by TVR with the system operating at 1.1 bar. It is imperative in this case though that the swirl pot cap is very well sealed and that the expansion vessel is free to vent. If not you will end up with a leak at the swirl pot or a vacuum drawn on cooling down respectively. Note that as the water expands and the the pressure cap relieves to the expansion chamber the nature of the "solid" system will result in sudden depressurisations of the system and then a steady pressure increase again, which will pulse the pressure.
Other way around.
Advantages
reverse of disadvantages above.
Plastic bottle acts a second "potential over pressure protection device"
Relief cap only relieves when pressure is excessive
Disadvantages:
Reverse of advantages of above
In this case the swirl cap cover (non pressure) must be well sealed and the pressure relief cap must also be well sealed to the expansion bottle.
In this mode the system will run at a lower pressure (probably around 0.8b judging by the water level changes in my expansion bottle from hot to cold) and as the water warms up the expanding water freeflows to the expansion bottle compressing the air at the top and slowly compressed the air building up a slight overpressure. As the air acts as an accumulator the system is not "solid" and as such pressure changes are mild in comparison to the mode of operation above.
As I started off saying it appears even TVR couldn't make up their mind and who's to say they didn't release a third tech memo reversing the second one again!!! But from a purely engineering fluid dynamic perspective either should work and it is really personal preference as to whether you want a solid system running at 15psi or a system with an accumulator running at a lower pressure. I personnally prefer the latter. BUT IN BOTH CASES YOU MUST MAKE SURE THE CAPS ARE SEALED OR VENTED AS STATED ABOVE FOR THE APPROPRIATE CONFIGURATION - THIS IS KEY IF YOU DON'T WANT TO BREAK ANYTHING
Mark
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