The purpose of plunger lift is to move the liquid at the bottom of the tubing toward the surface. Formation gas is the power source for moving the liquid. The plunger enables the gas to carry the fluid on its way to the surface. The control of time spent flowing, after-flowing and shut-in determines the action of the plunger. The amount of liquid to be carried and the volume/pressure of the gas are critical factors, also. Too much liquid can prevent the gas and plunger from making the trip up the tubing. Not enough fluid causes the plunger to rise too quickly, damaging the spring housing and plunger.
When the gas to liquid ratio is shifted toward liquid, then a more efficient plunger is required to conserve the gas supply. The goal is to make each MCF (thousand cubic feet) carry the maximum amount of liquid possible to the surface. An inefficient spiral plunger, for example, will let liquid slip downward, past the plunger, where it must be re-lifted a second or third time. When the gas available is below the critical rate, then a more efficient plunger is required. Efficiency is not the primary problem however, when there is sufficient gas available.