PT21 Inverted Bucket Steam Trap (Cast Iron)
Cast iron inverted bucket steam trap with stainless steel internals for equipment drains on medium to heavy, intermittent condensate loads, vertically mounted and rated to 17.5 bar(g) and 220°C.
Specifications
- Sizes
- DN 15, 20, 25, 40
- Operation
- Intermittent, cyclic (density difference between steam and water)
- Max allowable pressure (PMA)
- 17.5 bar(g)
- Max allowable temperature (TMA)
- 220°C
- Max operating back pressure
- 90% of inlet pressure
- Min differential pressure
- 0.1 bar
- Cold hydro test pressure
- 27 bar(g)
- End connection
- Screwed (NPT/BSPT/BSP)
- Installation
- Vertical, inlet from bottom and outlet at top; trap level below equipment; bypass above trap level
- Body material
- Cast Iron
- Internals
- Stainless Steel (AISI 304)
- Valve seat & pin
- AISI 410/420 (Hardened)
Overview
The PT21 is an inverted bucket steam trap in cast iron construction with all stainless steel internals, best suited for equipment drains with medium to heavy condensate loads on intermittent operation. It works on the density difference between steam and water to give a cyclic discharge of accumulated condensate, and the induction-hardened valve and seat give perfect shut-off with no steam loss over prolonged continuous service. Rated to 17.5 bar(g) maximum allowable pressure and 220°C, it is fitted vertically with the inlet at the bottom and the outlet at the top. Supplied, sized and serviced for steam systems across Nepal.
Features & Benefits
- The inverted bucket mechanism works on the density difference between steam and water, making it mechanically simple and robust with no temperature-sensitive element to fail, so it tolerates water hammer and superheat better than thermostatic or thermodynamic traps.
- High condensate handling capacity even at low pressure means a smaller trap size can serve a given load, which reduces cost and installation footprint versus oversizing.
- Induction-hardened valve pin and seat concentrate wear resistance on the two highest-wear parts, extending service intervals under continuous prolonged operation.
- Perfect shut-off with no steam loss directly saves energy compared to traps that leak live steam when worn, and those losses compound over the operating life of a steam system.
- The full internal kit (valve pin, seat, bracket, lever) is replaced as a matched set during maintenance, which restores the trap to as-new performance rather than patching individual worn parts.
- Priming at commissioning (cracking the inlet valve to fill the trap with water before steam enters) prevents the bucket from losing its water seal, which is the single most common cause of inverted bucket trap malfunction if skipped.
- Cast iron body keeps cost low for general low-to-medium pressure service, appropriate given the 17.5 bar(g) ceiling — for higher pressure or superheat, the cast steel PT23/PT24 variants are the correct step up.
Dimensions
| Model | Size (mm) | Size (inch) | Dia | A | Wt (kg) |
|---|---|---|---|---|---|
| PT21 | 15 | 1/2" | 115 | 155 | 3.70 |
| PT21 | 20 | 3/4" | 115 | 170 | 4.20 |
| PT21 | 25 | 1" | 186 | 282 | 16 |
| PT21 | 40 | 1.1/2" | 213 | 300 | 19 |
- All dimensions are in mm, weights in kg.
- Dimensions shown here are for indicative purposes only. Please contact our representative for exact dimensions.
Continuous Discharge Capacity
| Discharge Capacity (kg/hr of hot condensate) — Differential Pressure (bar) | ||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Model | Orifice (mm) | 0.25 | 0.5 | 1.0 | 2.0 | 3.0 | 4.0 | 5.0 | 6.0 | 7.0 | 8.0 | 9.0 | 10.0 | 11.0 | 12.0 | 13.0 | 14.0 | 15.0 | 16.0 | 17.5 |
| PT21-15 | 2.5 | 80 | 100 | 120 | 150 | 180 | 200 | 220 | 230 | 250 | 260 | 270 | 280 | 290 | 300 | 310 | 315 | 330 | 340 | 350 |
| PT21-15 | 2.8 | 100 | 115 | 140 | 180 | 205 | 240 | 260 | 275 | 290 | 305 | 325 | 340 | 360 | 375 | 385 | --- | --- | --- | --- |
| PT21-15 | 3.2 | 130 | 145 | 190 | 240 | 285 | 320 | 340 | 360 | 375 | 390 | --- | --- | --- | --- | --- | --- | --- | --- | --- |
| PT21-15 | 4.0 | 150 | 185 | 230 | 290 | 340 | 370 | 400 | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
| PT21-15 | 4.8 | 200 | 270 | 350 | 420 | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
| PT21-15 | 6.4 | 250 | 340 | 400 | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
| PT21-20 | 2.8 | 100 | 120 | 160 | 215 | 260 | 290 | 325 | 350 | 380 | 400 | 425 | 450 | 470 | 480 | 490 | 500 | 510 | 520 | 530 |
| PT21-20 | 3.2 | 125 | 145 | 185 | 250 | 300 | 340 | 380 | 410 | 450 | 480 | 500 | 520 | 540 | 560 | 580 | --- | --- | --- | --- |
| PT21-20 | 4.0 | 150 | 185 | 250 | 320 | 400 | 470 | 520 | 580 | 620 | 660 | 700 | --- | --- | --- | --- | --- | --- | --- | --- |
| PT21-20 | 4.8 | 230 | 310 | 410 | 510 | 600 | 670 | 720 | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
| PT21-20 | 6.4 | 300 | 380 | 500 | 680 | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
| PT21-25 | 4.8 | 300 | 380 | 460 | 620 | 790 | 930 | 1075 | 1200 | 1350 | 1475 | 1600 | 1725 | 1850 | 1950 | 2100 | 2200 | 2300 | 2400 | 2500 |
| PT21-25 | 5.6 | 400 | 510 | 700 | 940 | 1150 | 1325 | 1525 | 1700 | 1875 | 2025 | 2200 | 2350 | 2450 | 2500 | --- | --- | --- | --- | --- |
| PT21-25 | 6.4 | 500 | 640 | 880 | 1200 | 1450 | 1700 | 1950 | 2200 | 2300 | 2400 | 2500 | --- | --- | --- | --- | --- | --- | --- | --- |
| PT21-25 | 7.0 | 620 | 840 | 1150 | 1600 | 1950 | 2300 | 2500 | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
| PT21-25 | 7.9 | 900 | 1200 | 1500 | 2050 | 2400 | 2600 | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
| PT21-25 | 9.5 | 1300 | 1550 | 1900 | 2500 | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
| PT21-25 | 12.7 | 2200 | 2450 | 2800 | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
| PT21-40 | 6.4 | 450 | 550 | 760 | 1000 | 1150 | 1250 | 1350 | 1475 | 1575 | 1675 | 1775 | 1875 | 2000 | 2100 | 2200 | 2300 | 2400 | 2500 | 2600 |
| PT21-40 | 7.0 | 600 | 740 | 940 | 1250 | 1450 | 1650 | 1800 | 2000 | 2150 | 2300 | 2450 | 2575 | 2675 | 2800 | 2900 | 3000 | 3100 | --- | --- |
| PT21-40 | 7.9 | 800 | 940 | 1150 | 1450 | 1750 | 2000 | 2200 | 2400 | 2550 | 2750 | 2900 | 3100 | 3200 | 3300 | --- | --- | --- | --- | --- |
| PT21-40 | 8.7 | 900 | 1075 | 1300 | 1650 | 1950 | 2250 | 2550 | 2850 | 3100 | 3400 | 3600 | --- | --- | --- | --- | --- | --- | --- | --- |
| PT21-40 | 9.5 | 1000 | 1175 | 1450 | 1850 | 2250 | 2600 | 2900 | 3250 | 3500 | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
| PT21-40 | 11.2 | 1200 | 1450 | 1800 | 2400 | 2900 | 3300 | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
| PT21-40 | 14.3 | 1500 | 2000 | 2550 | 3000 | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
| PT21-40 | 19.0 | 2400 | 2800 | 3200 | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
- Discharge capacity in kg/hr of hot condensate against differential pressure in bar.
- Select a capacity equal to or higher than the condensate load after applying a safety factor of 2 to 3. Oversizing is not recommended.
- Example: inlet 4 bar(g), back pressure 1 bar(g), load 200 kg/hr, safety factor 2 → PT21-20, orifice 4.0 mm, 400 kg/hr at 3 bar differential.
Materials of Construction
| Component | Material |
|---|---|
| Body | Cast Iron |
| Cover | Cast Iron |
| Bucket Assembly | AISI 304 with CS reinforcing ring |
| Valve Seat (Hardened) | AISI 410/420 |
| Valve Pin (Hardened) | AISI 410/420 |
| Bracket | AISI 304 |
| Lever | AISI 304 |
| Plug | Carbon Steel |
| Gasket | Non CAF |
| Bolt | High Tensile |
| Nut | High Tensile |
| Pipe | Carbon Steel |
- All internal screws are AISI 304.


