Colloidal mixing of cementitious material into a liquid such as water to form a grout slurry for pumping to a location for use includes a mixing tank and a colloidal mixing mill which grinds and pumps the mixed material with the material being repeatedly circulated between the mill and the tank. The colloidal mixing mill includes a housing defining a generally cylindrical chamber containing a rotor shaped to define a clearance of the order of 3 mm between the front and rear wall of the housing and the rotor with holes from a dished front face of the rotor to the rear face to carry the mixed materials to the clearance where a shearing action takes place to shear the particles in the mixed materials prior to exit through the outlet.

A bathwater circulating system has a pump operable to draw fluid in at an intake port and expel it under pressure at an output port. Water- and air-supply conduits feed water and air to the intake port at a rate determined by a flow-restricting air-intake valve so that the pump mixes the water and the air, pressurizes the mixture and thereby dissolves the air in the water, and expels the air/water mixture at the output port. A pressure-reducing valve is connected by an output conduit that extends from the output port to the pressure relief valve and conducts the water/air-bubble mixture from the pump to the pressure-reducing valve without separation of the air from the water and such that the mixture is at least partially depressurized at the pressure-reducing valve such that the air forms microbubbles in the water.

A vapor hood for a proppant blending system, with a proppant entrance port to receive proppant, the proppant entrance port having a one way valve to allow the flow of proppant but prevent the backflow of vapor when the proppant is not entering the vapor hood.

A system for mixing fracturing gel includes a dry gel mixing chamber having a bladed impeller carried to rotate in the mixing chamber. The mixing chamber has a dry gel inlet and hydrating fluid inlet. A valve is fluidically coupled to the hydrating fluid inlet to automatically maintain a specified flow condition of hydrating fluid into the mixing chamber over multiple different values of the flow condition to the hydrating fluid inlet.