A second type of lift pump in light vehicle applications is the plunger pump. It is mounted on the in-line injection pump, and it’s driven by a cam inside the in-line injection pump housing.
Internally, a spring-loaded cam-follower converts the rotary motion of the camshaft into reciprocating motion. The reciprocating motion is transferred to a spring-loaded plunger, fitted with close tolerance in a cylindrical bore. It has two spring-loaded check valves - an inlet valve, and an outlet valve.
As the engine drives the injection pump, the lobe of the camshaft pushes the cam follower into the plunger pump. The cam follower acts directly on the plunger, pushing it towards the end of the cylinder bore. Fuel is displaced from one side of the plunger, through the outlet check valve, to the other side of the plunger.
When the cam follower retracts, spring force on the plunger moves the plunger out of the cylindrical bore. Fuel from the fuel tank enters behind the plunger through the inlet check valve. Fuel in front of the plunger is displaced out of the pump to the fuel injection system.
If the quantity of fuel required is reduced, so is the movement of the plunger.
A vane pump is used in distributor type injection pumps. It is also known as a transfer pump. It is mounted on the input shaft in distributor type injection, and pumps fuel whenever the distributor pump is driven by the engine.
It consists of a rotor, mounted off-center in a pump housing. Slots are machined in the rotor to carry vanes. As the rotor rotates, the vanes can move into, and out of, the slots. The vanes seal on the edges of the rotor slots and the pump housing.
As the pump rotor rotates, trapped fuel is carried around by the action of the rotor, until the leading vane uncovers the outlet port. Since the rotor is offset, as it turns further, the volume between the vanes reduces, and fuel is squeezed out of the pump. A pressure relief valve controls the pump’s operating pressure.
