header tank cap failure - datalogging results

[Colin Mill]

Hi Johnty

 

I'm sure removing the joggle valve is a big step forward. I'm sure part of your success is that you have good instrumentation and warm the engine up carefully etc. Without moving the tail of the header to the bypass you would still have the problem that should the stat stick shut you would also loose the pressurisation because, as things stand, the stat inhibits the flow through the header until it opens. This is partly my worry over the standard system - it doesn't seem fault tolerant - designing it so loosing the stat looses you pressurisation as well is a bit of a house of cards.

 

One of the reasons why I prefer the conventional systems is that they can pressurise to a pressure in excess of the vapour pressure of the fluid at the exit of the head. I see this as adding significantly to the tolerance of the system.

 

In the existing system the pressurisation is, at best, only marginally above the vapour pressure of the exit fluid from the head. However, there are going to be variations in the temperature in the head so it follows that there must always be areas within the head that are at a temperature higher than the head exit flow. At these points the vapour pressure will exceed the pressure of the system and since vapour pressure rises rapidly with temperature (about 6% for every deg C!) some local boiling is almost inevitable.