A poppet valve plays an important role in compressors, but how exactly? Here is all you need to learn and keep in mind.
A poppet valve is a mushroom-shaped valve that rises in a perpendicular manner from its seat. It is generally used in hydraulic and pneumatic systems or internal combustion engines and controlled via solenoids. It can also be set to normally-open or normally-closed in its de-energized state.
Poppet valves are often used as relief valves in order to prevent overpressure and check valves from facilitating one-way flows. They are often placed side by side with spool valves as alternatives for hydraulic/pneumatic systems. And at times, poppet valves are also referred to as engine valves.
Poppet Valve Design
Here’s how poppet valves work: these mushroom-shaped valves make use of balls or rounded stem tips – also known as poppets – to seal off passageways by pressing those poppets onto seats. This action occurs via the combination of spring force and fluid pressure. This is how the valve is when in its normally-closed position.
This valve can be opened mechanically (using a limit switch), manually, and electrically via a solenoid. The valve can also be opened pneumatically – i.e., with pilot air – which pushes a stem that efficiently draws the poppet right off its seat, thereby allowing fluid to flow.
A popular design is a 2-position, 3-way valve that permits fluid to flow, e.g., into a cylinder when the valve is set off. And it expels the emitted fluid into a reservoir when the valve closes or via an exhaust port.
On the other hand, spool valves use cylindrical elements – which usually come fitted out with O-rings that move in a linear fashion – within a bored valve body. When the spool shifts, the O-rings will open and close the ports alternately. This promotes seamless movement among these valve ports.
Spool valves are often said to be very balanced, i.e., they remain in position and can’t be displaced until external forces from a solenoid, manual operation, etc., acts upon them. Some poppet valves come in highly balanced designs that do not disappoint during operations.
Why Poppet Valves Are Considered Better Than Spool Valves
Both types of valves are typically used in hydraulic and pneumatic circuits. However, poppet valves seem to take the upper hand, especially in pneumatic circuits, while spool valves are the preferred choice for hydraulic systems.
One major reason for these choices/preferences is that opening poppet valves requires much greater actuating forces than what is required for equal-sized spool valves. This can become a significantly limiting component, especially with the greater pressures that hydraulic systems usually bring to bear. Poppet valves are designed to directly encounter system pressures, while spool valves often move at right angles to them.
Poppet valves have several benefits that spool valves cannot offer. Some of the benefits that come with using poppet valves include:
- Closed crossovers
- Faster response times
- Higher flow rates, especially from smaller packages
- Less prone to damages caused by contaminants
- Longer lifespans due to much lower friction
- Lower costs, etc.
Crossover has to do with the period via which a single port opens right before another one is fully closed. This is a highly crucial consideration, especially when precise control is of the utmost importance. And poppet valves take the upper hand in this regard and are considered the much better choice over spool valves.
Response time with poppet valves is much faster, and this is due to greater flow and shorter movements when the valve is open. However, the response is not consistent compared to spool valves, where pressures generally fluctuate.
Since poppet valves rely heavily on system pressure in order to close, using them is not highly recommended in vacuum applications or when downstream holding functions are required.
Spool valves, just like selector valves, can be easily configured in multifaceted or multipurpose arrangements. This is why it is common to see 4-way, 3-position spool valves all over the place. Three-way poppet valves can easily be used conjointly in order to double the action of 4-way spool valves.
Poppet valves, when used as check valves, may – or may not – integrate springs. However, this depends considerably on the design. Even though most poppet-style relief valves typically use springs, they are mostly pilot actuated.
Applications of Poppet Valves
Poppet valves are predominantly used for load lowering and load holding with single-acting cylinders. They are also employed as unloading devices in most positive displacement pumps. Air tanks use relief valves made of poppet valves,
Poppet valves provide suitable methods of flow reversal prevention within fluid circuits. And they have also found immense use in preventing the contamination of different media within mixing systems.
A few poppet check valves are designed to permit reverse flow, a typical example used extensively in hydraulic lifts. When used in that capacity, the check valves have to allow the fluid to flow into the cylinder to hold the piston in place.
In order to bring down the load, the fluid has to reverse its path via the valve. Lifting the poppet off its seat requires the use of external pilot pressure. And this allows the fluid to return to the valve via the outlet.
Facts About Poppet Valves
First off, poppet valves do not require lubrication in any way. This is a big plus when selecting those valves in which a significant consideration is a chemical compatibility with several fluids.
This makes poppet valves incredibly useful for systems that deliver nothing else but medical gases. They are also perfect for systems that need dry, clean air. Lubrication is not a problem to be considered seriously in hydraulic systems that use the hydraulic fluid as a lubricator, making spool valves functional.
Poppet valves are excellent at self-cleaning since the large relative valve orifice generates a large flow through it. This sweeps away all contaminates from dirty air.
Poppet valves are also less expensive to fabricate compared to their counterparts, i.e., spool valves. The latter requires high precision machined spindles and bored valve bodies.
An economical solution could be the duplication of a multipurpose spool valve with multiple 3-way poppet valves. Of course, this solution is perfect if the other characteristics of poppet valves – i.e., fast response, low wear, etc. – are advantageous and summarily factored in.
Final Thought
This post is a concise discussion of poppet valves, including their applications, design, and considerations or facts. More information on valves can be found on the official website of the Valve Manufacturers Association.