A steam trap is a valve installed in steam piping and equipment to automatically discharge condensate, air, and other non‑condensable gases while preventing steam leakage. The following describes its typical operating cycle.

1.The trap is installed between the steam‑heated equipment and the condensate return header. At start‑up, the bucket is at the bottom and the valve is fully open. Condensate enters the trap, flows to the bottom, and fills the body, completely submerging the bucket. The condensate then discharges through the fully open valve to the return header.

2.Steam also enters the trap through the bottom of the bucket, rising to occupy the top and creating buoyancy. The bucket gradually rises, moving the lever toward the valve seat until the valve closes completely. Air and carbon dioxide pass through small vent holes in the bucket and collect at the top of the trap; any steam released through these vents condenses due to heat loss from the trap body.

3.As incoming condensate begins to fill the bucket, the bucket exerts a pull on the lever. The force increases with the rising condensate level until it overcomes the differential pressure, opening the valve.

4.As the valve begins to open, the differential pressure across the disc decreases, and the bucket drops rapidly, allowing the valve to open fully. Non‑condensable gases accumulated at the top of the trap are discharged first, followed by condensate. As the water flows out of the bucket, it carries any accumulated dirt with it. Once condensate is discharged, steam re‑enters the trap, and the cycle repeats.