What is Valve Train for Diesel Generator Sets?

In today's world, electricity has become an indispensable part of our lives. Whether it is households, factories, or large commercial places, a stable and reliable power supply is of vital importance. As an important backup power source, diesel generator sets play a key role in the power system. And the valve train, as one of the core components of the diesel generator set, directly affects the working efficiency and service life of the entire generator set with its performance and reliability. This article will deeply explore the structure, function, and common faults and preventive measures of the valve train of diesel generator sets, helping you to better understand and maintain this important component.

The valve train is a key component of the diesel generator set. Its main role is to precisely control the opening and closing of valves according to the requirements of the internal combustion engine's working cycle, ensuring that fresh air (or mixture) can enter the cylinder in time, while maintaining the sealing of the combustion chamber during compression and expansion, and expelling the exhaust gases after combustion in time. In a four-stroke internal combustion engine, this process is achieved by timely opening and closing of intake and exhaust valves; while in two-stroke crankcase-scavenged internal combustion engines, the intake and exhaust are completed by the movement of the piston, so no special valve train is required. The performance of the valve train directly affects the efficiency and power output of the engine, and is an important guarantee for the efficient operation of the entire diesel generator set.

The structure and working principle of the valve train vary depending on the type of internal combustion engine and the configuration position of the valves. The commonly seen valve trains mainly include side-valve type and overhead-valve type.

The side-valve valve train is a relatively traditional design, with all components mounted on one side of the cylinder. Its main parts include intake valve, exhaust valve, valve spring, push rod, camshaft, and timing gears. The advantages of this design are simple structure, easy maintenance and repair, and the ability to form effective compression swirl, which is very beneficial for small internal combustion generator sets. However, it also has some obvious disadvantages, such as the combustion chamber not being compact enough, leading to poor knock resistance, greater heat loss, relatively higher intake and exhaust resistance, and higher HC emission levels. Therefore, the application of this valve train technology in modern diesel generator sets is gradually decreasing.

Working Principle:

When the crankshaft rotates, the camshaft also starts rotating through the timing gears.

When the cam lobe tip pushes the push rod, the push rod rises and opens the valve, while the valve spring is compressed.

When the cam lobe tip leaves the push rod, the valve quickly falls under the tension of the valve spring, causing the valve to close.

The overhead-valve valve train is the most widely used design in modern diesel generator sets. All of its components are installed on the cylinder head. In addition to including the valves, valve springs, push rods, and camshaft, it also has extra parts such as tappets and rocker arms. The advantage of this design is that it can form a more compact combustion chamber, reduce intake and exhaust resistance, and make the combustion process more efficient. At the same time, valve clearance adjustment is more convenient, heat loss of the combustion chamber is smaller, and under higher compression ratios, the cylinder height can be appropriately reduced, thereby reducing the engine size. Although the structure of the overhead-valve valve train is relatively complex, its performance advantages make it the first choice for most diesel engines.

Working Principle:

When the camshaft rotates, the cam lobe tip pushes up the push rod and tappet.

The tappet lifts one end of the rocker arm, causing the rocker arm to rotate around its shaft. The other end of the rocker arm presses on the valve stem, thereby opening the valve while the valve spring is compressed.

When the cam lobe tip passes, the valve closes under the force of the valve spring, and the rocker arm and tappet return to their original positions.

The wear or damage of valve train parts can seriously affect the performance of the diesel generator set. Once the valve timing is disrupted and the valve lift decreases, especially when the valve and valve seat are not tightly sealed, it will lead to reduced cylinder compression, which in turn causes power reduction of the internal combustion engine and increased fuel consumption. Therefore, understanding the causes of common faults and preventive measures is crucial to ensuring the normal operation of generator sets.

Valves not closing tightly

The main reason is poor fitting of the contact surface between the valve and valve seat due to wear, carbon deposits, or burning. In addition, bent valve stems or sticking in the guide, broken or weakened valve springs, and too-small valve clearance adjustment can also cause poor sealing.

Initial judgment of valve leakage: This can be preliminarily judged by testing the cylinder compression pressure. If cylinder compression pressure is low, inject a little oil into the cylinder and test again. If the pressure is still low, and there is intake backfire during operation, it indicates a leakage problem.

Valve clearance variation

In addition to excessive clearance adjustment, the main reasons are loosened valve clearance adjusting screws or normal wear of cam, tappet, and other valve train parts.

Fit problem between valve stem and valve guide

This is caused by improper selection of clearance, carbon deposits in the guide, or bent valve stems.

Valve breakage

This usually occurs at the stem groove area between the head and stem. The main cause of valve breakage is excessively high engine temperature, sudden cooling, uneven temperature distribution creating thermal stress, or incorrect installation of intake/exhaust valves leading to deformation and breakage.

Valve spring breakage

This may be caused by structural, material, or processing defects, or deformation during operation. In addition, prolonged use leading to weakened spring force can also cause valve spring breakage, destroying normal engine operation, and even leading to valves falling into the cylinder causing serious accidents.

Proper maintenance and servicing

Regularly check the contact surface between valve and valve seat, remove carbon deposits and worn materials in time to ensure tight fit.

Adjust valve clearance at specified intervals to ensure compliance with requirements. At the same time, check whether valve clearance adjusting screws are loose and tighten them in time.

Strictly select valve stem and valve guide according to clearance requirements, and regularly check for carbon deposits inside the guide. Once bent or deformed valve stems are found, replace the valve immediately.

Reasonable operation and usage

During operation, avoid excessive engine temperature. If abnormal temperature rise is found, take proper cooling measures, but never suddenly cool down to avoid thermal stress caused by uneven temperature distribution.

Ensure correct installation of intake and exhaust valves to avoid deformation or breakage caused by wrong installation.

Replace valve springs regularly to ensure sufficient elasticity. During disassembly and repair, clean the valve springs thoroughly, carefully check for cracks or severe rust, and check whether they stand straight or are twisted. Once these problems are found, replace springs immediately.

Professional inspection and adjustment

Conduct regular professional inspection of diesel generator sets, carefully check whether valves have twisting, deformation, or cracks. During inspection, ensure proper clearance between valve and guide, and ensure accurate valve seating to prevent major accidents caused by valve breakage.

For other valve train components, such as camshaft, tappet, etc., regular inspection is also necessary to detect and repair worn or damaged parts in time to ensure the valve train works properly.

As an important component of the diesel generator set, the valve train's structure and working principle play a decisive role in the performance and efficiency of the generator set. Understanding different types of valve trains and their respective advantages and disadvantages helps us make wiser decisions when selecting and using diesel generator sets. At the same time, being familiar with the causes of common valve train faults and preventive measures can help us better maintain generator sets, extend their service life, and ensure stable and reliable power supply at critical moments. In short, only by fully recognizing the importance of the valve train and taking scientific and reasonable management measures can we fully utilize the performance advantages of diesel generator sets to meet our growing demand for electricity.

Through the above detailed introduction and analysis, it is believed that you now have a more comprehensive and in-depth understanding of the valve train of diesel generator sets. In the future use and maintenance process, it is hoped that you can apply this knowledge into practice to ensure your generator set is always in good working condition, providing solid power support for your life and work.