A vacuum pump removes air from a container to create a vacuum. Force pumps of many types are used for vacuum pumps including Rotary pumps and Piston pumps.
This vacuum pump is a piston pump. With each cycle it removes a smaller number of air molecules until it just keeps up with what is leaking in past the joints and valve seats.
The amount of vacuum at that point depends on the quality of the components — how fast the valves close, how tight the seals are, etc.
A very common type of pump, this is one of many variations.
Power steering units often rely on a vane pump to obtain the pressure needed for the Power Cylinder. Automatic transmissions often use them too.
The vanes are in slots in the rotor. When the rotor spins, centrifugal force pushes the vanes out to touch the casing, where they trap and propel fluid. Sometimes springs also push the vanes outward.
When the vanes reach the return side they are pushed back into the rotor by the casing. Fluid escapes through a channel or groove cut into the casing, shown here on the lower right side in black.
On this vane pump there is considerable unbalanced force on the drive shaft, since the high-pressure, outlet area is all on one side. Vane pumps can be designed in balanced configurations where there are two inlet and two outlet ports, similar to balanced gear pumps.
A volute is a curved funnel increasing in area to the discharge port. It is often used with impeller pumps. As the area of the cross-section increases, the volute reduces the speed of the liquid and increases the pressure of the liquid.
One of the main purposes of a volute casing is to help balance the hydraulic pressure on the shaft of the pump. However, this occurs best at the manufacturer’s recommended capacity. Running volute-style pumps at a lower capacity than the manufacturer recommends can put lateral stress on the shaft of the pump, increasing wear-and-tear on the seals and bearings, and on the shaft itself.
This cutaway of a ‘high-end’ magnetic drive pump shows the volute wrapping around the impeller at the top and bottom. The ring to the left of the upper part of the volute is for lifting the pump and is located at the balance point.