B1H Inverted Bucket Steam Trap

B1H inverted bucket steam trap for compact steam drainage

Spirax Sarco B1H is a cast iron inverted bucket steam trap for smaller steam and condensate drainage points. It is supplied in 1/2 inch and 3/4 inch sizes with screwed NPT connections. The trap uses a mechanical inverted bucket mechanism, stainless steel internal components and a cyclic discharge action to remove condensate close to steam temperature. That combination gives plant designers a compact, serviceable trap for steam main drip stations and equipment drainage where the available differential pressure and condensate load have been properly established.

The B1H is a single product identity, while the technical capacity chart distinguishes pressure-range selections for the same trap family. A selection marked B1H-15, B1H-30, B1H-75, B1H-125, B1H-180 or B1H-250 is a pressure-range designation used for sizing and ordering; it must not be treated as a different base product page. The correct designation depends on both the maximum differential pressure and the capacity required at the minimum expected differential pressure.

How the B1H works

An inverted bucket trap responds to the difference in density between steam and condensate. The bucket mechanism changes the valve position as the service condition changes, producing a cyclic discharge rather than a continuously open drain. The technical information sheet states that condensate is discharged close to steam temperature. This makes the product a mechanical steam trap intended to separate condensate drainage from the live steam supply while retaining the pressure and temperature limits of the selected pressure range.

That operating principle is useful at drainage points where water must be removed reliably but the trap must remain small and maintainable. It does not remove the need for engineering checks: the trap must have enough capacity at the lowest available differential pressure, must not be exposed to a differential pressure above its selected limit, and must be installed so the bucket can move in its intended vertical plane. For a broader explanation of trap families and application decisions, use the steam trap selection guidance alongside the model-specific data below.

Maintainable cast iron construction

The B1H body and cover are cast iron, identified in the technical information sheet as ASTM A126 Class B. The bucket, valve head, valve seat and bucket arm are stainless steel; the valve head and seat are specified as hardened stainless steel. A graphite cover gasket provides the cover seal. This combination is designed around a serviceable mechanical assembly rather than a sealed disposable cartridge. The trap can be isolated and inspected without disturbing the piping connections, provided the installation includes suitable isolation and the system has been made safe before work begins.

An integral strainer is available as an option for the B Series. It can help protect the valve head and seat from dirt and scale at the trap inlet, but it is not a reason to omit good upstream line protection. The installation guidance calls for a pipeline strainer ahead of the trap. Select and maintain pipeline strainers and filters according to the cleanliness and flushing requirements of the complete steam system.

A bimetal air vent is also available as an option. The technical sheet describes rapid air removal during cold start-up and states that the vent closes at approximately 200 °F (93 °C), remaining closed during normal trap operation. The option should be considered when air removal at start-up is important, but its effect on the installed height and service access must be included in the layout.

Typical applications and practical boundaries

Official B Series information identifies steam main drip stations, laundry equipment, industrial dryers and storage tanks as typical applications. In each case, the B1H should be selected as part of the drainage arrangement rather than by pipe size alone. A drip station may have a light but continuous condensate load; a dryer or storage tank may have a different start-up load and a changing pressure differential. The trap size, pressure-range designation, inlet condition, return pressure and drainage geometry should therefore be considered together.

The product is intended for steam service and for the condensate or water generated by that service. The installation instructions also discuss air service for the wider inverted bucket range. Any use with another fluid requires a separate suitability check based on material compatibility, pressure, temperature and the consequences of a malfunction. No assumption should be made from the name of the fluid alone, especially where hazardous, corrosive or oxygen-depleted conditions are possible.

For superheated steam or a return system in which condensate may be lifted, the piping arrangement needs additional protection. A check valve may be required after the trap to prevent backflow when condensate is elevated. For modulating pressure conditions or superheated steam, the installation guidance calls for a check valve at the trap inlet to help prevent loss of prime. Review the available steam check valves as part of the system design rather than adding a valve after the trap has already been selected.

Pressure, temperature and differential-pressure limits

The B1H technical sheet separates pressure-shell design limits from the operating limit selected by the orifice. The maximum allowable pressure is 250 psig up to 450 °F, equivalent to 17 barg up to 232 °C. The maximum allowable temperature is 450 °F (232 °C) over the stated 0–250 psig shell condition. The maximum operating temperature is also stated as 450 °F (232 °C) at all operating pressures. These are boundaries for engineering review; they are not permission to use every pressure-range selection at every combination of temperature and pressure.

For Spirax Sarco B1H, the maximum operating pressure, or PMO, is determined by the selected orifice. The capacity chart provides six B1H pressure ranges: 1–15 psig (0.07–1 bar), 5–30 psig (0.34–2 bar), 10–75 psig (0.69–5 bar), 20–125 psig (1.4–9 bar), 60–180 psig (4.1–12.4 bar) and 125–250 psig (9–17 bar). Choose a pressure range that safely covers the maximum differential pressure while still providing the required discharge capacity at the minimum differential pressure. If a trap is subjected to pressure above its selected maximum differential pressure, the capacity chart warns that it will not open.

The B1H pressure and temperature limits are useful for screening an application, but the real selection case should include the pressure at the trap inlet, the pressure in the return line, start-up conditions, possible backpressure, the minimum operating differential pressure and the temperature at the trap. If the system limits are higher than the trap limits, a different selection and a suitable safety device are required. Local regulations may also restrict operation below the conditions quoted in the manufacturer’s documentation.

B1H steam trap sizing by capacity

The capacity chart reports continuous condensate capacity in pounds per hour, with kilograms per hour obtained by multiplying the listed value by 0.454. The values are for condensate discharged at approximately steam temperature; cold-water discharge capacity is much higher and should not be substituted for the steam-condensate case. Start with the normal condensate load, apply a safety factor of two or three times that load according to the application, and then check the chart against the available differential-pressure range.

Oversizing deserves particular attention with bucket traps. The official chart warns that an oversized bucket trap, especially on a light-load application such as a main drip, can lose its prime and pass steam. Under-sizing can fail to remove the load at start-up or at the minimum pressure differential. A sound selection therefore checks the complete operating envelope: capacity at the minimum differential pressure, the maximum differential pressure allowed by the selected orifice, and the actual load profile rather than a nominal pipe diameter.

Both 1/2 inch and 3/4 inch B1H connections share the dimensions and weight shown in the technical sheet: approximately 5 inches (127 mm) across dimension A, 4 inches (102 mm) across B, 3.3 inches (84 mm) across C, 3 inches (76 mm) across D and 1.4 inches (36 mm) across E. The C1 dimension is 3.8 inches (97 mm) where the bimetal air-vent arrangement applies. Approximate weight is 6.2 lb (2.8 kg). These envelope values help with clearance and support planning, but the selected pressure range and options still need to be confirmed before ordering.

B1H steam trap installation and system integration

The B1H technical information sheet specifies a horizontal installation so that the inverted bucket can rise and fall vertically. The trap should be positioned below and close to the equipment drain point, with the flow direction verified from the casting and the connected piping. An upstream pipeline strainer protects the seat and head from debris, while full-port isolation valves around the trap allow service without disturbing the rest of the line. Unions or other removable connections should be considered where they improve safe access.

At start-up, the installation instructions require the inlet valve to be opened slowly, followed by the outlet valve, to establish a water seal or prime around the inverted bucket. If there is not enough condensate to prime the trap, the body may need to be filled manually after isolation and safe preparation. Repeated loss of prime can indicate that the trap is too large for the load, so changing to a smaller pressure/capacity selection may be more appropriate than repeatedly reopening the bypass.

When condensate is discharged to a raised return, fit the required non-return protection. If the trap is used with modulating pressure or superheated steam, include the inlet check-valve arrangement described in the installation instructions. Any bypass should have reduced capacity and should be positioned above the trap; it should be avoided unless continuous service is genuinely necessary. If discharge is routed to atmosphere, place the outlet where hot condensate and flash steam cannot endanger people or equipment.

Outdoor service also needs planning. The installation instructions state that a trap in continuous operation will not freeze, but it can be damaged if steam pressure is lost or turned off. Because the B1H is not presented as self-draining, provide manual drainage or an approved automatic frost-protection arrangement where freezing temperatures are possible.

B1H steam trap maintenance and ordering checks

Before any B1H maintenance, isolate the trap from both supply and return, safely vent pressure to atmosphere, allow the temperature to normalise and verify that the equipment cannot be re-pressurised. The maintenance sequence includes checking the inlet passage and optional strainer screen, inspecting the body and cover for corrosion, examining the hardened head and seat for wear or wiredrawing, confirming that the bucket vent hole is clear and replacing worn gaskets or mechanism parts as required. The separate installation information provides the complete service sequence and model-specific tightening torques.

Before ordering, confirm the 1/2 inch or 3/4 inch NPT connection, normal and maximum condensate load, minimum and maximum differential pressure, return-line backpressure, operating temperature, horizontal installation space and any requirement for the optional strainer or bimetal air vent. The pressure-range designation should be selected from the B1H capacity chart; it is not safe to infer it from the pipe size or from a nearby B Series model. With those checks complete, Spirax Sarco B1H provides a clear, maintainable inverted bucket steam trap option for compact steam drainage points within its documented limits.