Various Valve Mechanisms

Various Valve Mechanisms - There are several types of valve mechanisms commonly used in car engines, including a valve mechanism with a side valve arrangement (SV), a valve mechanism with an overhead valve arrangement (OHV) and an Overhead Camshaft type valve mechanism ( OHC). Where the OHC type valve mechanism is a Single Overhead Camshaft (SOHC) valve mechanism and a Double Over Head Camshaft (DOHC) type valve mechanism.

Various Valve Mechanisms

1. “SV” Type Valve Mechanism

Valve position on the side valve type

The location of the valve is not placed on the cylinder head, but is located on the side of the cylinder block. The valves are driven directly by the camshaft through the valve lifter. The valve mechanics are not that complicated and have few components so the sound is not that loud.

Disadvantages of this type of side valve

The weakness of the engine with side valve arrangement is that the shape of the combustion chamber is not good so it is difficult to obtain high engine capabilities. Therefore the side valve arrangement is currently rarely used.

2. “OHV” Type Valve Mechanism

Valve position on the valve mechanism type Overhead Valve (OHV)

In the OHV type, the valves are placed on the cylinder head. The camshaft on the OHV type valve mechanism is located on the engine block. The components consist of: camshaft, valve lifter, pressure rod and trigger. How it works when the camshaft pushes up on the valve lifter, then the movement is transmitted by the pressure rod to the valve through the trigger so that the valve opens. The valve closes again due to the push of the valve spring after the cam is no longer in contact with the valve lifter.

The advantages of the Overhead Valve (OHV) type valve mechanism

The OHV type valve mechanism makes the combustion chamber more compact so as to obtain better performance. Therefore, this type of valve mechanism is widely used compared to the "SV" type.

3. “OHC” Type Valve Mechanism

Valve position on the Overhead Camshaft (OHC) valve mechanism type

In the OHC (overhead camshaft) type valve mechanism, the camshaft is located on the cylinder head. The number of camshafts on the OHC type valve mechanism is only one so it is commonly called SOHC (Single Overhead Camshaft) and there are also two in number called DOHC (Double Overhead Camshaft) or some call it "Twin Cam".

The advantages of the Overhead Camshaft (OHC) type valve mechanism

The advantage of the OHC type valve mechanism is that the valve mechanics are less so that opening and closing the valves is directly driven by the camshaft. This valve mechanism also reduces friction that may occur when the engine is operating, because the cam directly moves the valve.

Compared to other valve mechanisms, the OHC type is better because there is no delay in opening and closing the valves. On the other hand the mechanism

Disadvantages of the Overhead Camshaft (OHC) type valve mechanism

OHC type valves have the disadvantage that the cylinder head is more complex because of the camshaft and the engine is higher.

4. “DOHC” Type Valve Mechanism 

Valve position on Double Overhead Camshaft (DOHC) valve mechanism type

In the DOHC (Double overhead camshaft) type valve mechanism, the camshaft is located on the cylinder head.

The advantages of the Double Overhead Camshaft (DOHC) type valve mechanism

DOHC engines have a smoother sound and better engine performance when compared to vehicles that use SOHC mechanisms. Why is that so?

Because each shaft in DOHC has a different function, one shaft is to regulate the intake valve and the other is to regulate the exhaust valve. This is certainly different from the SOHC valve mechanism which uses one shaft to regulate the intake valve and exhaust valve at the same time.

DOHC has 2 camshafts that are placed above the cylinder head. 1 camshaft to open and close the intake valve and another camshaft to open and close the exhaust valve. The valve opening and closing system in DOHC technology no longer uses a rocker arm. In this condition the camshaft moves the valve directly, this makes the valve opening more precise and the power loss due to friction will decrease, which means it will increase the vehicle's performance.

The existence of 2 camshafts that are placed above the cylinder head on a DOHC engine allows vehicle manufacturers to apply multi-valve to a DOHC engine. In short, more than one valve can be installed on one cylinder. Currently, vehicle manufacturers generally install a model of 2 intake valves and 2 exhaust valves for each cylinder. So if your car has 4 cylinders and the engine uses a DOHC valve mechanism, then the number of valves is 16. That's why on the vehicle on the hood there is usually a DOHC 16 valve inscription.

That's a brief discussion of the various valve mechanisms in vehicles.