What is A Fuel Feed Pump for Diesel Engine?

A Fuel Feed Pump, also known as a fuel transfer pump, is a crucial component of a fuel system in a vehicle, generator, or any other type of machinery that requires fuel to function. The purpose of a Fuel Feed Pump is to transfer fuel from the fuel tank to the engine’s fuel injection system at the correct pressure and volume.

 

 

Fuel Feed Pump

In this article, I will discuss Fuel Feed Pumps.

Fuel Feed Pump–

Fuel Feed Pump comes in various types, including mechanical and electric pumps. Mechanical Fuel Feed Pump is typically used in older vehicles and is driven by the engine’s camshaft or a dedicated shaft. They rely on a diaphragm or plunger to draw fuel from the tank and push it toward the engine. On the other hand, electric fuel feed pumps are more common in modern vehicles and use an electric motor to draw fuel from the tank and transfer it to the engine.

Fuel feed pumps operate on the principle of positive displacement, which means that they deliver a consistent amount of fuel to the engine regardless of the engine’s demand. This is essential to ensure that the engine always receives the correct amount of fuel to run efficiently and avoid damage. Fuel Feed Pumps are also designed to maintain a specific fuel pressure, which is necessary to achieve the optimal fuel-air mixture for combustion.

In addition to transferring fuel to the engine, Fuel Feed Pumps also play a critical role in removing air and vapor from the fuel system. Air and vapor can form in the fuel tank and lines due to temperature changes or a low fuel level. These pockets of air can disrupt the fuel flow and cause the engine to run poorly or stall. Fuel feed pumps use a venting system to remove any air or vapor in the fuel system and maintain a consistent flow of fuel to the engine.

 

Fuel Feed Pump Design–

The fuel feed pump is constructed as a single-acting Fuel Feed Pump or double-acting Fuel Feed Pump and is usually provided with a hand-priming device and preliminary filter. Both diagrams are shown below. 

Single-acting Fuel Feed Pump- 

Single-acting fuel feed pump.

The revolving cam or eccentric presses the plunger of the Fuel Feed Pump downwards by means of the roller tappet and pressure spindle. A portion of the fuel present in the suction chamber equal to the swept volume or quantity of fuel delivered per stroke(or air for lack of fuel) is delivered through the pressure chamber and the plunger spring is compressed in an intermediate stroke. Toward the end of this stroke, the spring-loaded pressure valve closes again. 

 

The pressure spindle, roller tappet, and plunger are only in slight contact with one another. As soon as the cam has passed its maximum stroke, the plunger, pressure spindle, and roller tappet accordingly move upward due to the pressure exerted by the plunger spring. A portion(quantity delivered per stroke) of the fuel pressure in the pressure chamber is thereby delivered to the injection pump(delivery stroke) through the filter. Fuel is, however, also suctioned simultaneously from the fuel tank to the suction chamber through the preliminary filter and the suction valve. 

 

During the delivery stroke(spring actuated), all the fuel swept out by the plunger in the pressure chamber is fed to the injection pump. The volume of this, however, is slightly less than that swept out by the plunger in the suction chamber. The volume swept out in the pressure chamber is the volume swept out in the suction chamber less the volume of the spindle reaching into the pressure chamber. Therefore, during the intermediate stroke, a quantity of fuel corresponding to the volume of the spindle is fed to the injection pump. 

 

Where the pressure in the feed pipe exceeds a specified value, the plunger spring lifts the plunger only a part of the stroke. The fuel quantity delivered per stroke is thus correspondingly smaller. Hence, the higher the pressure in the feed pipe, the smaller the quantity delivered. The Fuel Feed Pump is made elastic. If the overflow valve is clogged, pressure in the feed pipe would quickly rise to such an extent that the feed pump would stop functioning. The pipe is thus safe against excessive pressure. Fuel leaking along the pressure spindle is returned to the suction chamber through the leakage channel.

Double-acting Fuel Feed Pump- 

Double-acting fuel feed pump.

The revolving cam or eccentric process the plunger of the feed pump downwards by means of the roller tappet and pressure spindle. This uses a suction valve and a pressure valve to open, and the plunger spring is tensioned. Both suctioning and feeding thus take place simultaneously. 

 

Once the cam or eccentric has passed its maximum stroke, the plunger rises due to the action of its spring, and the fuel is sucked and fed to the injection pump through the other two valves, thus both suctioning and feeding again occur simultaneously. This is a double-acting fuel feed pump delivering fuel twice with every revolution with its camshaft. As the plunger, roller tappet, and pressure spindle are again only in slight contact with one another, feeding is likewise elastic. The fuel quantity delivered can not approach zero as with a single-acting pump. Because of this, an overflow valve is necessary for the pressure tube or the fuel filter. 

 

Fuel Feed Pump Diagram–

Fuel feed pump diagram.

Fuel feed pump for diesel engine- 

Fuel has to be fed to the diesel engines of the vehicles under the pressure of about 1 atm(gauge) as the quantity of fuel delivered would otherwise be inadequate. Only in stationary engines and some tractors, a gravity feed tank can be placed at so high a level as to provide sufficient pressure. Hence in diesel-driven vehicles, fuel has to pump to the injection pump. The fuel feed pump has been designed to meet this demand. 

 

You can see the Fuel Feed Pump diagram in the upper section. 

How does a Fuel Feed Pump work under varying loads?

A Fuel Feed Pump is a critical component of a fuel system that ensures the engine receives the right amount of fuel at the correct pressure and volume. The fuel feed pump works differently under varying loads, and its performance is crucial for the engine’s optimal operation. This article discusses how a fuel feed pump works under varying loads and its importance in maintaining the engine’s efficiency.

Under varying loads, the engine’s fuel demand changes, and the Fuel Feed Pump‘s performance must adjust accordingly. For example, when the engine is idling or operating at a low speed, the fuel demand is low, and the Fuel Feed Pump‘s output is minimal. The pump adjusts its output by regulating the fuel pressure through the pressure relief valve. The pressure relief valve reduces the pressure in the fuel system, which reduces the pump’s output, ensuring that only the required amount of fuel is delivered to the engine.

As the engine’s load increases, its fuel demand also increases, and the fuel feed pump’s performance must adjust to meet this demand. In this case, the pump increases its output to maintain the correct fuel pressure and volume. The pump’s diaphragm or plunger moves faster to draw more fuel from the tank and deliver it to the engine.

When the engine operates at maximum load, the fuel demand is high, and the fuel feed pump must deliver fuel at the maximum possible rate. Electric fuel feed pumps can deliver fuel at a much faster rate than mechanical pumps, and they are better suited for high-performance engines that require a high fuel flow rate. Electric pumps use an electric motor to drive the pump’s diaphragm or plunger, which can deliver fuel at a much higher rate than a mechanical pump.

A fuel feed pump’s performance can also be affected by the fuel system’s condition, including fuel filter clogs, fuel line leaks, or damaged fuel injectors. These conditions can cause the fuel feed pump to work harder to deliver the required fuel volume and pressure, leading to increased wear and tear on the pump. Regular maintenance of the fuel system is essential to ensure the fuel feed pump’s optimal performance.

What drives Fuel Feed Pump? 

The Fuel Feed Pump is attached to the injection pump and driven by its camshaft i.e. either by a cam also diving a pump element of the injection pump, or by eccentric mounted between two cams. It is advisable to use an eccentric for driving at higher speeds. 

 

Mechanical fuel feed pumps are common in older vehicles, and they are driven by the engine’s camshaft or a dedicated shaft. The mechanical pump’s diaphragm or plunger is moved by a lever that is driven by the engine’s motion, providing the required pumping action. The engine’s motion drives the camshaft, which in turn drives the fuel pump’s plunger, drawing fuel from the tank and delivering it to the engine.

Electric fuel feed pumps are common in modern vehicles and use an electric motor to draw fuel from the tank and transfer it to the engine. The pump’s electric motor is powered by the vehicle’s electrical system, typically through a relay or switch that is controlled by the engine’s computer. The electric pump’s diaphragm or plunger is driven by the motor, drawing fuel from the tank and pushing it towards the engine at the correct pressure and volume.

The electric fuel feed pump has several advantages over the mechanical pump, including better fuel efficiency, smoother operation, and the ability to deliver fuel at a much higher rate. The electric pump can also be located anywhere in the fuel system, making it easier to install and maintain.

Conclusion–

In summary, a Fuel Feed Pump is a vital component of a vehicle or machinery’s fuel system. Its primary function is to transfer fuel from the fuel tank to the engine’s fuel injection system at the correct pressure and volume. Fuel feed pumps play a crucial role in maintaining a consistent fuel flow to the engine and removing air and vapor from the fuel system. It is essential to ensure the fuel feed pump is in good working condition to ensure the engine runs smoothly and efficiently.