The low pressure fuel pump is installed on the high pressure fuel pump (on the rear cover of the speed controller) and is designed to supply fuel from the tank through the coarse and fine filters to the high pressure pump

KAMAZ low pressure fuel pump

The low-pressure fuel pump is driven by the eccentric of the high-pressure fuel pump camshaft through the pusher and its rod 13; consists of a body 1, a piston 12 with an eye 10 held by a plug 11, a rod 13, a pusher with a sleeve, suction 8 and discharge 3 valves with springs (Fig. 1.).

A manual piston-type fuel priming pump is fixed with a hollow bolt on the low-pressure pump housing. Therefore, the cavity under its piston communicates with the over-piston cavity of the low-pressure fuel pump.

low pressure fuel pump diagram

The fuel priming pump consists of an aluminum cylinder and a plastic piston with a rubber sealing ring and is designed to fill filters, fuel lines with fuel and remove air from the fuel system before starting the engine.

When the piston 8 (Fig. 2) is moved upwards with the help of the handle, a vacuum is created under it, the suction valve 6 opens and the fuel enters the B cavity of the low pressure fuel pump.

During the reverse movement, piston 8 presses on the fuel, the suction valve closes, and the discharge valve 10 opens and fuel is supplied to the fine filter.

After pumping the system, piston 8 is lowered down and its handle is fixed in the lower position by turning, while the piston is pressed tightly against the gasket.

In order to keep the helical groove on the stem working in contact with the steel pin, turn the plastic handle with pressure on it.

Piston 5 of the low pressure fuel pump makes two strokes: preparatory and working.

The preparatory stroke occurs when the piston moves upwards: under the action of the rotating eccentric 1, the pusher 2 and the rod 4 push the piston 5 upwards, compressing the spring 9.

In this position of piston 5, pressure is created in the suction cavity B, and vacuum is created in the discharge cavity A and the fuel is displaced by piston 5 into the A cavity through channel C .

At the same time, part of the fuel, equal to the volume occupied by the rod in the A cavity, enters the fine filter.

The working stroke occurs when moving down: the protruding part of the eccentric moves away from the pusher, and the piston under the action of a compressed spring 9 moves down and displaces fuel from cavity A into the fine filter.

At the same time, a vacuum is created in the B cavity, and it is filled with a new portion of fuel through the opened suction valve 6.

The low pressure fuel pump delivers more fuel than is needed to run the engine. Therefore, if the stroke of the pump piston is constant all the time, the pressure in the fuel line increases rapidly.

When the fuel flow decreases, the pressure in cavity A rises and the compressed spring cannot overcome the back pressure of the fuel.

As a result, the piston stroke decreases and the piston freezes, loses contact with the pusher, and the fuel supply by the pump decreases accordingly.

As the fuel consumption of the engine increases, the pressure in the A cavity decreases, the piston stroke increases and the fuel supply by the pump increases.