Inverted Bucket Steam Traps are mechanical steam traps actuated by a float responding to changes in condensate level.

Mechanical steam traps are density detectors and therefore also have difficulties venting air and non-condensable gases. Mechanical steam traps employ either an open or a closed float to actuate a valve. Closed float mechanical steam traps usually employ a secondary thermostatic air vent which allows the trap to discharge air rapidly. The air vent, of course, is an extra component which can fail open, causing the loss of steam, or fail closed and prevent the trap from discharging condensate. Closed float steam traps are usually large in physical size. This, combined with a float that is fragile to external pressure, and the continuous presence of condensate within the trap, make this device unsuitable for high pressure applications or installations where water hammer or freeze-ups can be expected.

On the positive side, mechanical steam traps respond to changes in condensate level only, independent of temperature or pressure. They respond rapidly to changing loads. Condensate discharge temperatures follow closely the saturation curve and they have a modulating (rather than an on-off) type of discharge. They are extremely energy efficient.

Open float mechanical steam traps share many characteristics with closed float traps. One major difference, of course, is the open float as found in an inverted bucket steam trap. The open float is no longer a weak point, because it cannot be collapsed by excessive pressure. Venting is usually accomplished by means of a small vent hole in the top of the bucket. This is a compromise, as the efficiency of the trap is affected by the sizes of the vent. The larger the vent the better the air handling, but at the expense of higher steam losses. A smaller vent has the opposite effect. The end result is a trap that is relatively efficient, but which does not remove air rapidly during start-up conditions. It discharges near steam temperature with an on-off action and the discharge temperature follows the saturation curve.

All mechanical steam traps are position-sensitive and can be installed only in their intended orientation.

Inverted Bucket Steam Traps.jpg

Inverted bucket steam traps are members of the mechanical trap category, using an open "inverted bucket" as a float. The trapping principle utilizes the difference in density between steam and water.

The construction of the trap is such that the trap inlet leads into the bottom and open end of the inverted bucket. Discharge is through an outlet valve above the inverted bucket.

Steam entering the inverted and submerged bucket, causes it to float and close the outlet valve, preventing discharge of steam. Steam in the bucket both condenses and leaks through the vent, allowing the bucket to sink and open the valve to discharge condensate. The weight of the bucket must be sufficient to overcome the closing force created by the differential pressure across the valve. Inverted bucket steam traps discharge condensate intermittently very near saturation temperature.

Any air or non-condensable gases entering the trap will also cause the bucket to float and the valve to close. Since they cannot condense as steam does, those gases will cause the trap to remain closed. In order to overcome this problem, the bucket has a hole to vent air and steam. The size of this vent hole has to be relatively small to prevent excessive loss of steam in addition to the air.

While most inverted bucket steam traps utilize a linkage system to obtain their desired action, one particular design uses no linkage at all and uses a free floating open spherically-shaped float in its design execution.

Prior to selecting a steam trap for your application, review steam traps selection with its advantages versus disadvantages and additional steam trap types: Disc Steam Traps, Piston Steam Traps, Lever Steam Traps, Closed Float Steam Traps, Open Bucket Steam Traps, Bimetallic Steam Traps, Bellows Steam Traps, Liquid or Solid Expansion Steam Traps (Wax Capsule Steam Trap), and Orifice Steam Traps.