How Does A Hydraulic Valve Lifter Work?

A Hydraulic valve lifter is a component in an internal combustion engine that helps to control the operation of the engine valves. A valve is a device to close and open a passage. In motor vehicle engines, two valves are used for each cylinder to operate the maximum output.  Here in this article, I will discuss the Hydraulic valve lifter and its working principle- 

Hydraulic valve lifter
Hydraulic valve lifter

Hydraulic Valve Lifter

Hydraulic valve lifter is now used in many engines. It is very quiet in operation because it ensures zero valve tappet clearance. It automatically adjusts its length to compensate for differences in valve tappet clearance. Also, it usually requires no adjustment in normal service. Variations due to temperature changes and wear are taken care of hydraulically.

Fig. shows a popular design of a hydraulic valve lifter. Its body consists of a cylinder and an oil reservoir. An opening in the body is connected with an oil pressure line from the engine lubricating system to supply the reservoir with oil. A plunger fits inside the cylinder so that its upper-end contacts the bottom of the push rod; and its lower end is supported by oil between it and the bottom of the cylinder.

Working Principle

Working principle of hydraulic valve lifter
Working principle of Hydraulic valve lifter

When the valve is closed as at (a) (cam on the lower side), oil from the reservoir opens the ball-check valve and raises the plunger by passing between it and the cylinder bottom. This produces zero clearance between the lifter unit and push rod, and between the rocker arm and valve stem.

When the cam turns to lift the lifter as at (b) (cam on the upside), the ball-check valve closes to prevent the return of oil to the reservoir; and causes the entire lifter unit to lift the push rod to open the valve. Because the lift starts with zero clearance, the noise is reduced to a minimum.

As shown in (b) during the lifting operation, a certain amount of oil is allowed to leak between the plunger and the cylinder, which causes the lowering of the plunger to produce clearance if the spring did not raise it again when the pressure on the plunger is relieved by the closing of the engine valve. This reopens the ball check valve, oil again comes beneath the plunger and the lifter is again set for zero clearance.

Advantages of hydraulic valve lifter– 

There are many advantages of using a hydraulic valve lifter. Here are some examples- 
  • A hydraulic valve lifter increases engine longevity by reducing engine wear and tear. 
  • It also decreases mechanical noise and provides quiet engine operation.
  • The hydraulic valve lifters allow for smoother and more consistent valve operation, resulting in less energy being lost as heat and improved fuel efficiency.
  • The hydraulic valve lifter has a better throttle response, which helps changes in engine R.P.M.


Although hydraulic valve lifters may have a higher initial cost compared to mechanical lifters, the benefits in terms of improved engine performance, longevity, and reduced maintenance costs make them a cost-effective solution in the long run.

Frequently Asked Questions(FAQ)

What is a valve? 

A valve is a device to close and open a passage. The valves are used in modern passenger cars or bike engines. The valves are operated by cams mounted on a camshaft. 

What is valve tappet clearance? 

Valve tappet clearance is a slight clearance between the valve tappet and the valve stem in the case of a straight poppet valve, and between the rocker arm and valve stem in the case of the overhead poppet valve.  It is also called Valve Lash. 

How many types of valves are used in an automobile vehicle? 

In motor vehicle engines, two valves are used for each cylinder- an inlet or intake valve, and an outlet or exhaust valve. 
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