A plunger pump in hot melt units operates using compressed air. The pump usually contains a double-acting plunger pump, which pumps glue in both the downstroke and upstroke. The pump is self-lubricating, meaning it deliberately leaks a little glue along the pistons. The plunger pump usually gives an increased glue pressure relative to air pressure, the multiplier is often printed on the pump. A commonly used ratio is 1:12 or 1:8. Thus, the plunger pump has regular tipping points. With a single-acting plunger pump must be waited until the piston is at the very top again; with a double-acting plunger pump, the turning point is short. If continuous flow is required with a very stable hot-melt caterpillar, then a gear pump possibly an option. A gear pump is a positive displacement pump that can pump a lot of volume relative to a plunger pump, but at a lower pressure.
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