Armstrong B and BI Series float and thermostatic (F&T) steam traps combine high standards of performance and long life with economy for heating service where continuous drainage with high air-venting capacity is required. Because of the wide use of vacuum returns in systems of this type, the thermostatic air vent element is charged to give it the capability of compensated response to the pressure-temperature curve of steam at any pressure from less than 500 mm Hg (20") vacuum to 2 bar (30 psig) gauge. B and BI Series F&T traps will vent air at slightly below steam temperature throughout this entire range of operation.

All B Series traps, except the 1/2" and 3/4", have inlet connections on both sides of the body to provide flexibility in piping. The BI Series F&T traps in sizes 1/2", 3/4" and 1" feature the convenience of in-line connections with the same internals as the B Series.

Working Principle and Features

The working principle of the float trap is based on the opening and closing action of the lever float mechanism caused by the change of condensate level in the valve body.

1. Start-up: When the equipment starts, the main valve is usually closed, and air is discharged through the open thermostatic vent by the system pressure. When condensate enters the valve, the float rises to open the main valve to discharge condensate, while the remaining air continues to be discharged through the thermostatic vent.
2. Normal Operation: When steam enters the valve, the thermostatic vent closes, and condensate is continuously discharged through the main valve. The liquid level in the trap changes with the flow rate of condensate, automatically adjusting the discharge rate.
3. Air Venting: During condensate discharge, air from the system accumulates at the top of the trap. When the air temperature drops below the saturation temperature of the corresponding pressure, the thermostatic vent opens to discharge the air.

Key Features:

• Stainless steel float, helium arc welded to prevent dissimilar metal penetration and corrosion.
• Stainless steel internals; valve and seat are hardened and ground to improve cavitation resistance.
• Robust float mechanism with good wear resistance, capable of withstanding high destructive pressure and water hammer.
• Excellent air venting performance. The inlet is at the top and the outlet at the bottom, preventing water seals from blocking air discharge at low pressures.
• Unaffected by back pressure. Condensate discharge is controlled by the liquid level, so return line pressure does not hinder normal operation.
• Built-in thermostatic air vent automatically discharges air and carbon dioxide.

Maximum Operating Conditions

• 15B, BI: 1 bar (15 psig) saturated steam
• 30B, BI: 2 bar (30 psig) saturated steam
• Maximum back pressure: 99% of inlet pressure

Maximum allowable pressure (vessel design):

• Model B2-B3: 8.5 bar @ 178°C (125 psig @ 353°F)
• Model B4-B8: 12 bar @ 191°C (175 psig @ 377°F)

WARNING

Cast iron traps should not be used in systems where freezing, excessive hydraulic or thermal shock are present.

Materials and Connections

Connections: Screwed BSPT and NPT. Flanged EN 1092-1 or ASME B16.5 (screw on) on request.

Component	Material
Body and cap	ASTM A48 Class 30 Cast Iron
Internals	All stainless steel — 304
Valve	Stainless steel — 303 or 440
Seat	Stainless steel — 303 (ASTM A582) / 440F in 1-1/2" and 2"
Thermostatic air vent	Stainless steel and bronze with phosphor bronze bellows, caged in stainless steel

Dimensions and Weights

Model No.	B2 / B3	B4	B5	B6	B8	BI2 / BI3 / BI4
Pipe Connections (mm)	15 - 20	25	32	40	50	15 - 20 - 25
"B" Height (mm)	124	140	140	189	244	143
"C" Face-to-Face (screwed) (mm)	98	124	117	146	194	127
"D" Bottom to Center (mm)	22.2	25.4	31.0	36.5	42.9	68.0
"H" Width (mm)	137	152	197	214	295	168
Weight in kg (screwed)	2.7	3.9	5.0	8.6	18.1	4.4

Capacity Charts

Options

Integral vacuum breaker. Add suffix VB to model number.

Many times, condensate will be retained ahead of steam traps because of the presence of a vacuum. To break a vacuum, air must be introduced into the system by means of a vacuum breaker. For maximum protection against freezing and water hammer in condensing equipment under modulated control, vacuum breakers are recommended. Armstrong B and BI Series F&T traps are available with integral vacuum breakers. Maximum pressure is 10 bar (150 psig).

DANGER

Do not use a conventional vacuum breaker open to the atmosphere in any system that incorporates a mechanical return system that carries pressure less than atmospheric pressure. This includes all return systems designated as vacuum returns, variable vacuum returns or subatmospheric returns.

Installation and Maintenance

1. Before installing any trap, blow down the piping that leads to the unit's inlet. Use full line pressure.
2. Install the trap inlet below the liquid level of the equipment to be drained. Make inlet piping as short as possible.
3. To allow maintenance and provide maximum service, install a valve on each side of the trap and a downstream testing tee. All valves should be of the full-ported type to avoid restricting flow. Provide a strainer ahead of the inlet.
4. Install a union downstream of the trap unless the discharge line is open and short.

Maintenance: Armstrong F&T steam traps are designed for easy accessibility during maintenance. The entire operating mechanism is attached to the cap. Pipe connections are made to the body. You should inspect the internal mechanisms of these traps at least once a year.