Open 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.

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Open bucket steam traps are rarely used today. As with other mechanical steam traps, they utilize the difference in density between steam and water.

When condensate first enters the trap, it fills the trap body and causes the bucket to rise and close the valve at the top of the trap. If entrapped air is removed, condensate will continue to enter the trap, finally spilling over into the bucket. This causes it to sink and open the valve allowing discharge of condensate. When steam arrives, it pushes the condensate out of the bucket through the syphon tube, which in turn refloats the bucket and closes the valve. As the steam in the trap condenses, additional condensate enters the trap and the cycle is repeated.

This type of trap requires an auxiliary thermostatically activated air vent, similar to that used in the float & thermostatic trap (Closed Float Steam Traps).

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, Inverted Bucket Steam Traps, Bimetallic Steam Traps, Bellows Steam Traps, Liquid or Solid Expansion Steam Traps (Wax Capsule Steam Trap), and Orifice Steam Traps.