Whenever you’re choosing between 3 and 4 way valves for pneumatic circuits, you should always be sure to take the internal design of the valve into consideration. While a valve’s fundamental function may be the same – the use of a poppet or spool valve could have a significant impact on your application. Below, we explain what each type of valve is and the benefits of using each.

Poppet Valves
Poppet valves are components that cover internal passages and are held in place by a combination of air pressure and (usually) a spring. The pressure created holds the valve in an unactuated position but when activated by steam, the poppet moves away from the seat to allow for airflow.

Poppets generally require a greater surface area, but also allow for a higher flow rate than a spool component. Because there’s less of an ongoing transitional state, wear and tear on this type of valve is greatly reduced, meaning that you’re far more likely to get a greater product lifespan out of a poppet valve than you would from similar spool pneumatic valves. Between their long lifespan and their increased flow, they make an excellent choice for your Pneumatic Circuits.

Humphrey’s brand of poppet valves has another built-in benefit that allows the valve to be more tolerant of sediment and debris than your generic spool valves. This can help provide faster response rates and longer lasting life.

Spool Valves
Spools are valve components that feature side mounts along its surface. When it’s actuated, the spool shifts and causes seals to travel along the bores, opening ports to allow for greater air flow. Generally speaking, they come in three different types: lapped/shear design with no seals, dynamic seals or O-rings.

One of the best features of spool valves is that they can moonlight as selector valves, providing the ability to choose from high and low pressures or vacuum pressure – making them an intriguing, cost-effective option for 4 way configurations but generally don’t provide the user with the kind of versatility that the Humphrey Poppet design would. They’re also not affected by pressure and because of it- less force is needed to actuate the valve.

With both Poppets and Spools, there are uses and counter-uses to consider as well. Spools have low flow rates while Poppets allow for significantly more. Spools are great for locking pressure downstream and Poppets are not. The real issue comes down to leak rate.

Lapped spool valves almost always have higher leak rates which makes them unacceptable for control of medias other than air, or limited sources of gas tanks, bottles, etc. As such, they’re generally better suited for factory automation where leak rates aren’t as strict/critical. It’s this same limitation that generally makes them less than desirable for vacuum where contaminates are ingested into the lines.

While which valve you use will be largely determined by the design of your circuit, these should help you make the right choice based on some of the factors we mentioned. However, if you’re looking for the more versatile of the two – we recommend the Humphrey Poppet Valve.