Accumulators are needed whenever a line must remain running for a splice or precise cut. Pneumatic accumulators are the simplest accumulator control for the control engineer and operator to understand.
The accumulator pressure works against web tension. The accumulator pneumatic pressure is preloaded to empty the accumulator (lower pressure than tension) or to fill the accumulator (more pressure than tension). If a web break or other slack condition occurs, an empty accumulator is preloaded and will begin to fill automatically.
When a known stop condition occurs, such as an unwind splice, the pressure on the full accumulator can be decreased slightly to hold tension while the splice is made. Web is fed from the accumulator. Pneumatic pressure on the accumulator establishes web tension. Once the splice is made, the pressure can be increased slightly and the unwind over sped to fill the accumulator.
When a known stopping condition such as making a square cut to length is made at the winder, the pressure on the accumulator can be increased slightly to fill the. Once the cut is made, the pressure can be decreased slightly and the winder may be over sped to empty the accumulator with good tension control.
We note that the tension levels will change slightly when the web stops and a pneumatically loaded accumulator is used. We also notice a snap in tension when the accumulator maxes out or bottoms out and the web path changes from serpentine to straight-through.