GESTRA BK 45 Bimetallic Steam Trap PN 40, DN 15-25

A bimetallic steam trap with built-in air venting for drip and tracing duties

The GESTRA BK 45 is a bimetallic steam trap with Duo stainless steel plates and a stage nozzle. At start-up the trap is fully open, so cold condensate and air leave quickly. As the temperature rises the bimetallic plates bend and pull the stage nozzle into the closed position, which happens just below saturation temperature, and thermodynamic effects in the stage-nozzle chamber support closing. The trap vents air automatically at start-up and during operation, and the BK 45 and BK 46 can also be used for thermal air venting in steam systems.

The family covers four types in DN 15, 20 and 25 (1/2, 3/4 and 1 inch), all PN 40: BK 45 (standard), BK 45-U, BK 45-LT for low temperatures, and BK 46 with a Cr-Mo body for higher temperature.

Technical specifications

Pressure ratings for the other flange standards and for BK 45-LT and BK 46 Class 150 and Class 300 are printed in the data sheet. The traps are designed for fluids of group 2 under the pressure equipment rules, and they have no ignition source of their own, but static charge and leakage must be considered by the plant operator when classifying hazardous zones.

Choosing between BK 45, BK 45-LT and BK 46

BK 45 suits general steam mains drains, tracing and heater drains up to 22 bar differential pressure. Choose BK 45-LT where the trap sees low ambient temperatures, since its body is SA 350 LF2 rated from -46 C. Choose BK 46 where the line needs the 1.5415 body, a 32 bar differential pressure limit and ratings up to 450 C. A bimetallic trap discharges condensate somewhat below steam temperature, so it is not the first choice where condensate must not back up into the process.

Install it with the strainer hanging downwards, and avoid insulating the trap or the condensate line so that the trap can dissipate heat; insulation can cause malfunction. See also the GESTRA UNA 16 for continuous drainage and other items under steam and clean steam equipment.

How the GESTRA BK 45 works

The trap opens fully at start-up, so cold condensate and air leave fast. As the temperature rises, the bimetallic plates bend and move the stage nozzle toward closed. The trap closes a little below the steam temperature, so the condensate leaves a little cooler than saturation. The trap also vents air by itself during operation.

Where the BK 45 is used

• Steam line drip points
• Steam tracing
• Thermal air venting in steam systems
• Heat exchangers and heaters
• Low temperature duty with the BK 45-LT

Selection checklist for the BK 45

• Type, BK 45, BK 45-U, BK 45-LT or BK 46
• Size of DN 15, 20 or 25
• Steam pressure and temperature
• Differential pressure
• End connection
• Body material
• Face-to-face length
• Spare regulator

Installation, commissioning and maintenance notes for the BK 45

Fit the trap below the point to be drained, with the flow in the direction of the arrow. Check that the line has no dirt left from construction. Open the steam slowly and watch the discharge. Replace the thermostatic regulator and the gasket as a set when the trap is serviced.

Requesting a quotation for the GESTRA BK 45

Please send the type, the size, the end connection and the steam data. Seven Star LLC serves industrial customers in Oman and the GCC and replies with a quotation based on the information provided.

BK 45 types

The four types are BK 45, BK 45-U, BK 45-LT and BK 46.

BK 45 sizes

The sizes are DN 15, 20 and 25, which are 1/2, 3/4 and 1 inch, all in PN 40.

BK 45 pressure rating

The PN 40 flanged rating is 40.0 barg at 20 degrees C, with a differential pressure of 22 bar.

BK 45 body materials

The BK 45 body is 1.0460 or SA 105. The BK 45-LT is SA 350 LF2. The BK 46 is 1.5415 or A182 F1.

BK 45 regulator

The regulator is made from Duo stainless steel plates with a graphite and CrNi gasket.

BK 45 end connections

The choices are flanges, screwed sockets, socket-weld and butt-weld through transition pieces.

BK 45 length

The flanged length is 150 mm for DN 15 and 20 and 160 mm for DN 25.

BK 45 weight

The flanged weight is 3.7 kg for DN 15, 4.3 kg for DN 20 and 4.8 kg for DN 25.

Trap records for the BK 45

Record the type, the size and the date of each check.

Choosing the right BK 45 type

Choose the BK 46 where the temperature or the differential pressure is higher than the standard type allows.

Documents and quotation

The attached GESTRA data sheet 810436 lists ratings, materials, dimensions and spare parts. Send the steam pressure, differential pressure, line temperature, end connection standard and type for a quotation, and confirm the variant and certificates before ordering.