Controlled Disc Trap
Controlled Disc Steam Trap Operating Principles
The controlled disc trap is a time-delayed device that operates on the velocity principle. It contains only one moving part, the disc itself. Lightweight and compact, the controlled disc trap meets the needs of many applications where space is limited.
In addition to the disc trap's simplicity and small size, other advantages include resistance to hydraulic shock, the complete discharge of all condensate when open, and intermittent operation for a steady purging action.
How It Works
 | Step 1 At start-up, the disc is pushed off its seat by any air or condensate entering the trap. When the steam enters the trap, it passes through the reduced area at the face of the disc, increasing in velocity and, therefore, decreasing in pressure. Some of the steam is discharged directly into the outlet stream, but a portion of it (along with some entrained condensate) passes to a control chamber above the disc. The disc snaps shut because the pressure in the control chamber above acts on the whole disc, while the inlet pressure of the high-velocity steam acts only on a small area of the disc. | |
 | Step 2 A small bleed groove across the disc allows the steam and air to bleed out of the control chamber over time. When the force above the disc is overcome by the force of incoming steam, condensate or air on the face of the disc, the trap opens, discharging condensate that has accumulated during the cycle. | |
Some manufacturers provide a steam jacket around the control chamber to prevent the blow-through of live steam when the trap is exposed to environmental conditions such as cold temperature or rain. Others supply insulating covers for the same purpose.
Armstrong CD Features
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| 1. | Constructed of carbon steel and stainless steel. |
| 2. | Small, lightweight design. Available over a range of pressures and capacities. Several pipe sizes and connecting fittings available. | |
| 3. | Valve requires maximum differential pressure. Operation hampered by low inlet pressure or by back pressure. | |
| 4. | Violent snapping action of disc can wear the seat, causing short service life. | |
| 5. | Small orifices can become blocked by dirt and scale. | |
| 6. | Simple mechanism, no linkage. | |
| 7. | Condensate often cools below steam temperature before removal. | |
| 8. | Fits into limited space. | |
| 9. | Resistant to corrosion, freezing and water hammer. |
