A poppet valve is a type of valve that consists of a hole or chamber, usually round or oval in cross-section, and a plug, usually a disk shape on the end of a shaft, that is lifted in and out of the hole to control the flow of fluid or gas.
The word poppet comes from the Middle English word for a doll or puppet, which can be moved by strings or wires. Similarly, the poppet valve is moved by a cam, a solenoid, a spring, or a manual lever.
Poppet valves are widely used in internal combustion engines, where they regulate the intake and exhaust of the air-fuel mixture and the combustion products. They are also used in other applications, such as pneumatic and hydraulic systems, where they provide fast and precise control of the fluid flow.
Types of Poppet Valves
There are two main types of poppet valves: normally closed and normally open.
- A normally closed poppet valve is one that remains closed when there is no pressure difference or force applied to it. To open the valve, the plug must be pushed away from the hole by a cam, a solenoid, or a manual lever. This type of valve is used to allow fluid or gas to enter or exit a system when needed. For example, in an internal combustion engine, the intake valves are normally closed and open when the piston moves down to create a vacuum in the cylinder.
- A normally open poppet valve is one that remains open when there is no pressure difference or force applied to it. To close the valve, the plug must be pulled towards the hole by a spring, a solenoid, or a manual lever. This type of valve is used to stop or restrict fluid or gas from entering or exiting a system when needed. For example, in an internal combustion engine, the exhaust valves are normally open and close when the piston moves up to compress the air-fuel mixture.
The following table summarizes the main differences between the two types of poppet valves:
| Type | Normal State | Opening Force | Closing Force | Example |
|---|---|---|---|---|
| Normally closed | Closed | Cam, solenoid, or lever | Spring | Intake valve |
| Normally open | Open | Spring | Cam, solenoid, or lever | Exhaust valve |
Applications of Poppet Valves
Poppet valves have many advantages over other types of valves, such as slide or rotary valves. They have no sliding or rotating parts on the seat, which reduces friction and wear. They can operate at high speeds and pressures, and can seal tightly and reliably. They can also handle a wide range of fluids and gases, from liquids to steam.
Some of the common applications of poppet valves are:
- Internal combustion engines: Poppet valves are used to control the intake and exhaust of the air-fuel mixture and the combustion products in gasoline and diesel engines. They are driven by a camshaft that rotates in sync with the crankshaft. The timing and duration of the valve opening and closing are critical for the engine performance and efficiency
- Steam engines: Poppet valves are used to control the admission and release of steam in steam engines. They are driven by an eccentric or a valve gear that is connected to the crankshaft. The valve events are adjusted to match the speed and load of the engine
- Pneumatic and hydraulic systems: Poppet valves are used to control the flow of compressed air or hydraulic fluid in various devices, such as cylinders, actuators, pumps, and motors. They are driven by solenoids, springs, or manual levers. They can provide fast and precise switching and modulation of the fluid flow
- Tyres: Poppet valves are used as inflation and deflation valves in pneumatic tyres. They are driven by the pressure difference between the inside and outside of the tyre. They can prevent air leakage and maintain the desired tyre pressure
- Torpedoes: Poppet valves are used to control the expulsion and recovery of compressed air and seawater in torpedo launchers. They are driven by solenoids or springs. They can reduce the noise and bubble trail that might reveal the submarine’s position