VALVE MECHANISMS USED IN ENGINES

The Valves are actuated by cams mounted on a cam shaft. Different types of valve operating mechanisms are

i) Side valve Mechanism

ii) Over head valve Mechanism

iii) Over head inlet and side exhaust valve mechanisms.

* Side Valve Mechanism

The cam mounted on the camshaft operates the valves tappet during its rotation. The valve tappet is pushed up. The valve tappet pushes the valves from its sheet against the spring force. Thus, the valve is opened. When the cam is not in action, the valve returns back to its seat by the valve spring and spring retainer.

* Over head Valve Mechanism

Here, the valves are located in the cylinder head. When the cam rotates, the valve lifter will push the push rod upwards. Push rod moves the rocker arm. Since, the rocker arm is pivoted at its Centre , it pushes the valves off its seat against the spring force. Thus, the valve is opened. When the cam is not in action, The valve returns back to its seat by the valve spring and spring retainer.

* Overhead Inlet and Side exhaust Valve Mechanism

In this system, inlet valve is located in the cylinder head whereas the exhaust valve is located in the cylinder block. The inlet valve is actuated by overhead valve mechanism. The exhaust valve is actuated by side valve mechanism.

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Advantages And Disadvantages Of Air Refrigeration System :

Advantages Of Air Refrigeration : 1. The refrigerant used namely air is cheap and easily available. 2. There is no danger of fire or toxic effects due to leakages. 3. The weight to ton of refrigeration ratio is less as compared to other systems. Disadvantages Of Air Refrigeration : 1. The quantity of Refrigerant used per ton of refrigeration is high as compared to other systems. 2. The COP of the system is very low. Therefore running cost is high. 3. The danger of frosting at the expander valves is more as the air contains moisture content.

ELECTRICAL COMPARATORS AND ITS WORKING

Electrical Comparators are used as a means of detecting and amplifying small movements of a work contacting elements. An electrical comparator consists essentially of a pick-up head or transducer for converting a displacement into a corresponding change in current and a meter or recorder connected in the circuit to indicate the electrical change, calibrated to show in terms of displacement. Generally, an amplifier is needed to provide the requisite sensitivity and to match the characteristics of different parts of the circuit. Electrical comparators can be classified according to the electrical principle used in the pick-up head. Most of the comparators use either a differential transformer, an inductance bridge, a strain gauge or a capacitor as a means of detecting movement of the gauging element. There are different types of electrical comparators. One kind called an electrolimit gauge is used to check or measure the outside diameter of a roll. The objec...

THROTTLE GOVERNING OF STEAM TURBINES

Steam Pressure at inlet to a steam turbine is reduced by throttling process to maintain the speed of the turbine constant at part load and hence this method of governing is called "Throttle Governing". Construction : Throttle governing system consists of a centrifugal governor, a lever , an oil pump , a pilot piston , control valve , a relay piston and a throttle valve. The throttle valve is moved by a relay piston. The relay piston is actuated by pilot piston control valve. There are two piston valves covering ports in the pilot piston control valve without any overlap. These piston valves are operated by lubricating oil supplied by a gear pump at 2 to 4 bar. The oil returns to the drain from this chamber. Working : When the turbine works on full rated load, the throttle valve will remain open. When the load is decreased, the energy output of the turbine becomes in excess and the turbine shaft speed increases. Hence, governor sleeve will lift. The upward movemen...

Mechinopedia For Mechanical Engineers

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