Why cannot the auxiliary exhaust valve of the expansion tank in a heat transfer oil boiler be left open for an extended period during operation?
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I know this will cause high-temperature oxidation of the heat transfer oil in the expansion tank. I want to know how the oil temperature in the expansion tank rises I want to know the specific details and reasons. I’m a beginner; could some experienced teacher give me some guidance? Thank you
It’s affected by the system temperature! I use a T55 heat transfer oil system; when adjusting the temperature at the boiler outlet or according to the heat demand of end-users, the temperature of the expansion tank changes.
If the auxiliary exhaust is opened, it will directly connect the sump to the high-temperature oil and gas in the system, which is the main cause of over-temperature in the sump.
Auxiliary exhaust allows the return pipeline of the heat transfer oil to be directly connected to the expansion tank; its purpose is to facilitate rapid exhaust during oil heating adjustments and when new oil is added to the system. The standard practice of most manufacturers is to shut it down when the temperature exceeds 180 degrees Celsius during testing ； During normal operation, it must be strictly turned off. Because if the auxiliary exhaust pipe is opened, the temperature of the expansion tank will be affected and will become very high ； Even by creating a small circulation directly through the auxiliary exhaust pipe and the oil in the expansion tank, the oil temperature in the expansion tank will essentially be equal to the return oil temperature of the system. Generally speaking, in open systems, it is not recommended that the oil temperature in the expansion tank exceed 70°C.