Middle consistency pulp is a suspension of fibers, water and air / gas. The relative air-gas content increases with the pulp consistency and modern and efficient MC-pumps include a degassing system with an internal or external vacuum pump.
A pulp with a consistency of 15% (dry solid concentration) will contain up to 35% of air-gas
MC-pumps are centrifugal pumps but the casing of an MCpump is connected to a vacuum pump evacuating the air to avoid the formation of an air / gas pocket.