Gaseous-fluid pumps are designed to increase the efficiency of pumps in high gasto-liquid ratio (GLR) wells.
The stationary part of the gas-fluid pump consists of a short barrel and an extension, forming a chamber between them. The plunger is long enough to bridge the chambers and create a seal during the pumping cycle. The plunger moves completely in and out of each pump barrel throughout the cycle. During the upstroke, the turbulence and low pressure cause the gases in the fluid to expand, separate and rise to the top of the suction chamber. In the previous pump cycle, the fluid in the intermediate chamber was pressurized after contacting the total liquid column. The remaining gas in this fluid is under pressure and the gas to liquid volume ratio is lower than the volume ratio of the fluid entering the pump.

During the downward stroke, the free gas rises towards the top of the chamber. As the plunger continues downward, gas and liquid are trapped in the intermediate chamber. When the fluid below the swimming valve is expelled, the valve opens, allowing gas and fluid to flow up through the plunger. When the plunger is near the bottom of the stroke and the chamber is open at the top, the trapped gas escapes and rises through the fluid. When the chamber is closed again on the upstroke, the fluid gas content in the chamber has been reduced to a minimum

Proper valve spacing minimizes the clearance between the stroke valve and the fixed valve, thereby maximizing the compression ratio and increasing the total volume of fluid delivered per stroke. Gas-fluid pumps are primarily assembled from API type RH components and are supplied in API cups or API mechanical holddowns.

Because the chamber of the gaseous fluid pump is too large, it is not recommended for oil wells that contain a lot of sand or solids, which are prone to sand sticking.
https://youtu.be/3HYBVkJM9kU