The inverted bucket steam trap relies on the density difference between steam and condensate to work. When the bucket is full of condensed water and non-condensate gas, the vent on the upper part of the bucket removes the non-condensate gas. The bucket loses buoyancy and drives the valve core to move down. The trap opens to drain. When steam enters the bucket after draining, the bucket floats and drives the valve and the core closes the trap. Inverted bucket traps have 90% back pressure rate or more.
