1. The removal of oil and gas from a pipeline.

2. The difference in pressure between that which opens a safety valve and that which closes it.

3. A technique used to remove periodically accumulated solids in process vessels, boilers in particular, which would otherwise cause problems of deposition on heat transfer surfaces, foaming, and adverse effects on process performance. A blowdown vessel is used to receive a large amount of water and precipitated solids removed under boiler pressure.