Zuigslag

Zuigslag, in Dutch, refers to the suction stroke of a reciprocating piston engine or pump. It is the phase during which the cylinder volume increases, causing a drop in pressure and drawing fluid—air or a air-fuel mixture in engines, or liquid in pumps—into the cylinder through an inlet valve or suction port.

In four-stroke internal combustion engines, the zuigslag is the first stroke of the cycle. The intake valve opens (and the exhaust valve is closed or only partially open). The piston moves downward, expanding the cylinder and pulling the charge into the cylinder. The amount drawn in is influenced by throttle position, engine speed, and intake restrictions, and determines the engine’s volumetric efficiency and potential power. After the zuigslag, the compression stroke begins as the intake valve closes and the piston moves upward to compress the charge.

In two-stroke engines, the concept is related but less distinct, since intake and compression often occur during overlapping portions of the cycle due to scavenging. The term can still be used to describe the phase in which fresh charge enters the cylinder.

In reciprocating pumps, the zuigslag is the initial stroke: as the piston retracts, fluid is drawn into the cylinder through a suction valve, creating a pressure deficit relative to the source. This is followed by the discharge stroke, which pushes the fluid out of the cylinder.

The zuigslag is contrasted with the uitlaatslag (exhaust stroke) and the drukslag (compression stroke). Its efficiency depends on valve timing, throttle, and intake system design.