Trap primed, air off, bucket down, trap valve open.
Trap in service, bucket floating. Air passes through bucket vent and collects at top of trap.
Water enters bucket to replace air passing through bucket vent. This increases weight of bucket until...
...pull on lever cracks valve. Air at top of trap escapes, followed by oil and water. Liquid in pipe ahead of trap enters bucket followed by air.
Air displaces liquid and excess oil from bucket, restoring condition shown in Step 2.
Inverted Bucket Compressed Air Drain Traps
For heavy oil/water service
BVSW (bucket vent scrubbing wire) inverted bucket drain traps are designed for systems with heavy oil or water services. An inverted bucket is used because the discharge valve is at the top, so oil is discharged first, and the trap body is almost completely filled with water at all times.
The 1/16" scrubbing wire swings freely from the trap cap and extends through the bucket vent. Its function is to prevent reduction of vent size by buildup of solids or heavy oil in the vent itself. The up-and-down motion of the bucket keeps the vent clean and full size.
Operation of the inverted bucket drain traps
- Since there is seldom enough water to float the bucket and close the valve, the trap must be primed on initial start-up or after draining for cleaning. Step 1 (See drawing) shows “after operating” primed condition with oil in the top of the bucket and a very thin layer of oil on top of the water in the trap body.
- When valve in line to trap is opened, air enters bucket, displacing liquid. When bucket is two-thirds full of air (See drawing), it becomes buoyant and floats. This closes the discharge valve. As bucket rises, the vent scrubbing wire removes oil and any dirt from the bucket vent. Both liquid and air in trap are at full line pressure, so no more liquid or air can enter the trap until some liquid or air escapes through the discharge valve. Static head forces air through bucket vent. The air rises to top of trap and displaces water that enters bucket at bottom to replace air that passes through vent. Just as soon as bucket is less than two-thirds full of air, it loses buoyancy (See drawing) and starts to pull on valve lever as shown in Step 3.
- Note that liquid level at top of trap has dropped and the liquid level in the bucket has risen. The volume of water displaced by air exactly equals the volume of water that entered the bucket. During this valve-closed part of the operating cycle—Steps 2 and 3—water and oil are collecting in the horizontal line ahead of the trap. When the bucket is about two-thirds full of liquid, it exerts enough pull on lever to crack open the discharge valve.
- Two things happened simultaneously (See drawing). a) The accumulated air at top of trap is discharged immediately, followed by oil and any water that enters the trap while the valve is cracked. b) Pressure in trap body is lowered slightly, allowing accumulated liquid in horizontal line to enter the trap. Air displaces liquid from the bucket until it floats and closes the discharge valve, restoring the condition shown in Step 2 (See drawing).
- When full buoyancy is restored, the trap bucket is two-thirds full of air. Oil that has entered while the trap was open flows under bottom of bucket and rise to top of water in trap body. The trap normally discharges small quantities of air several times per minute.