Inverted Bucket Steam Traps — Armstrong International

Product Description

Inverted bucket steam traps are mechanical devices used throughout industrial steam systems to automatically discharge condensate and non-condensable gases while retaining live steam. The “inverted bucket” refers to the open-bottom float bucket inside the trap body that rises when steam is present—closing the discharge valve—and sinks when condensate accumulates, allowing the valve to open and drain the system. This cycling action keeps steam distribution lines free of liquid water, protecting equipment and maintaining thermal efficiency.

Armstrong International, headquartered in Three Rivers, Michigan, became one of the best-known manufacturers of steam system products in North America. The company supplied inverted bucket steam traps to refineries, chemical processing plants, paper mills, power generation facilities, shipyards, and large commercial and institutional buildings throughout much of the twentieth century. Their traps were standard equipment in settings where high-pressure steam was central to operations—environments that also frequently involved asbestos-containing insulation, packing materials, and ancillary components throughout the same piping systems.

Because steam traps operate at elevated temperatures and pressures, they were typically surrounded by, connected to, or installed alongside a wide range of thermally insulating materials. This context placed steam trap installation and maintenance workers in close proximity to asbestos throughout the product’s working life.

Asbestos Content

Inverted bucket steam traps themselves are primarily mechanical and metallic assemblies—cast iron or stainless steel bodies, valve seats, and the bucket mechanism. However, litigation records document that asbestos-containing materials were associated with these products in several important ways.

First, the gaskets and valve packing used to seal steam trap connections and internal components were historically made from compressed asbestos fiber or woven asbestos yarn. These materials were standard sealing solutions for high-temperature, high-pressure applications through the 1970s and into the early 1980s, when regulatory pressure and asbestos substitutes began to displace them. Plaintiffs alleged that Armstrong International and its distributors supplied or recommended asbestos-containing gaskets and packing as companion materials to their steam traps.

Second, steam trap installations were invariably embedded within larger insulated piping networks. Pipe insulation, fitting covers, valve insulation jackets, and block insulation surrounding the traps themselves were routinely manufactured with chrysotile or amosite asbestos throughout the mid-twentieth century. Workers who installed, repaired, or replaced steam traps necessarily disturbed this surrounding insulation as part of their work.

Third, insulating cement and finishing cements used to coat steam fittings and repair insulation around steam traps frequently contained asbestos binders, adding another potential source of fiber release at worksites where these traps were serviced.

How Workers Were Exposed

A range of industrial trades came into contact with inverted bucket steam traps over the course of normal operations. Litigation records document that the following work activities created conditions for asbestos fiber release and inhalation.

Pipefitters and steamfitters installed and connected steam traps to distribution lines, cutting into existing insulated pipe runs, removing and replacing insulation sections, and applying gaskets and packing at each connection point. This work generated dust from both gasket material and surrounding pipe insulation.

Industrial maintenance workers and stationary engineers performed routine trap testing, cleaning, and repair. Inverted bucket traps require periodic inspection—bucket mechanisms wear, valve seats erode, and internal components need replacement. Each maintenance event potentially involved breaking insulated joints, removing old gasket material by scraping or wire brushing, and cutting new gaskets from sheet stock, all of which plaintiffs alleged released respirable asbestos fibers.

Insulators applied and repaired the thermal coverings around steam lines and the traps integrated into them. Their work involved cutting, shaping, and fitting asbestos pipe insulation and block insulation in direct proximity to steam trap locations.

Boiler operators and plant operators in refineries, chemical plants, and power stations monitored and maintained steam distribution systems as part of their regular duties, potentially accumulating exposure over years or decades of working near disturbed insulation and worn gasket materials.

Shipyard workers encountered steam traps in marine engineering spaces aboard naval and commercial vessels, where asbestos insulation was pervasive and ventilation was often limited, increasing the concentration of airborne fibers during maintenance activities.

Litigation records document that exposure was not limited to a single trade or event. Workers in these environments typically encountered steam traps and their associated asbestos materials repeatedly across long career spans, which plaintiffs alleged resulted in significant cumulative fiber inhalation. OSHA’s subsequent regulation of asbestos in general industry—establishing permissible exposure limits and work practice requirements under 29 C.F.R. § 1910.1001—reflected the recognized hazard associated with disturbing asbestos-containing gaskets, packing, and insulation in exactly these types of industrial settings.