Raadster
24-07-2008, 04:54 AM
Ive seen the use of expansion tank in auto cascades and lower stages in regular cascades, i understand why there is a need for them since this systems are working with higher pressure gases, but what i wanna know is how the affect the system once its properly charged.
So my understanding of an expansion tank is to keep BP low enough while the system isnt in use so that the compressor can start, this BP is obviously lowered by the extra internal volume the expansion tank adds to the system.
My question is ive seen expansion tanks used in lower stage systems that are connected to the suction line using a short piece of captube. Now apparently when the system if off the captube will allow gas to enter the tank thus adding that extra volume and lowering system BP.
These are the things i don't get, when you are charging your system you will have gas enter that expansion tank, so your charge isn't the amount that is just enough for a system without that extra volume, but has that extra volume already being used. Doesn't that defeat the purpose?
Also if you added some valve to stop any gas entering the expansion tank while charging, and then opened that valve once the system was properly charged wouldnt there be a certain amount of gas always present thereafter remaining in the expansion tank?
For example if your BP was 150psig while the system was off and you turned the system on, the suction side pressure for the system is say 30psig, wouldn't enough gas be sucked out of the expansion tank until it had an internal pressure equaling that of the suction line.
This would mean that the expansion tank would therefore be taking a certain amount of charge out of the system that we could never retrieve unless the suction side ran in a vacuum?
Any clarification or links to material explaining this would be appreciated.
So my understanding of an expansion tank is to keep BP low enough while the system isnt in use so that the compressor can start, this BP is obviously lowered by the extra internal volume the expansion tank adds to the system.
My question is ive seen expansion tanks used in lower stage systems that are connected to the suction line using a short piece of captube. Now apparently when the system if off the captube will allow gas to enter the tank thus adding that extra volume and lowering system BP.
These are the things i don't get, when you are charging your system you will have gas enter that expansion tank, so your charge isn't the amount that is just enough for a system without that extra volume, but has that extra volume already being used. Doesn't that defeat the purpose?
Also if you added some valve to stop any gas entering the expansion tank while charging, and then opened that valve once the system was properly charged wouldnt there be a certain amount of gas always present thereafter remaining in the expansion tank?
For example if your BP was 150psig while the system was off and you turned the system on, the suction side pressure for the system is say 30psig, wouldn't enough gas be sucked out of the expansion tank until it had an internal pressure equaling that of the suction line.
This would mean that the expansion tank would therefore be taking a certain amount of charge out of the system that we could never retrieve unless the suction side ran in a vacuum?
Any clarification or links to material explaining this would be appreciated.