Fluid Power FAQ

Answers To Common Fluid Power Questions

Our Certified Fluid Power Pneumatic Specialists field important questions about fluid power products every day. Here are some of the queries we receive most often—and answers that can help you make the most of your products. Still have questions? Simply contact one of our specialists today.

Q: I hooked up all my pneumatic valves, put them on a manifold and provided fittings and plugs for every port on the pneumatic valves and manifold. However, my system merely extends once and then will not retract. What is the problem?

A: A common mistake people make is to plug the pilot exhaust port, which restricts the pilot air from escaping. If pilot air cannot escape, it remains in the pneumatic valve and prevents the valve from shifting.

Although the pilot exhaust port may be connected to a muffler, it should never be plugged. The pilot exhaust port must be able to exhaust in order for the valve to shift.

Q: I have an application that requires some side load on my pneumatic cylinder. What cylinder is best for side load applications?

A: Most round body cylinders are not preferred for side load applications. Since their piston rods are not supported, side force of the load can cause premature failure.

Guided cylinders have additional guide rods that help support the piston rod. Guided cylinders are preferred in many side load applications.

Q: My pneumatic cylinder doesn’t stroke fast enough at the end of stroke. Any suggestions?

A: Add a quick exhaust valve at the exhaust port of the pneumatic cylinder. A quick exhaust valve allows air to exhaust at the cylinder location instead of forcing the air to exhaust downstream through a valve, accelerating the rate at which the air can exhaust and thus improving the speed of the stroke.

Q: When would I use a metal seal or rubber seal spool valve?

A: Metal seal spools work best in clean, dry air. Under ideal operating conditions, metal seal spools can yield an extended life. However, air that is not clean and dry contains rust and contaminants that can ruin the spool.

Rubber seal spools are more forgiving under operating conditions where the air quality may be compromised.

Q: I have solid state switches on my pneumatic cylinder and I need to know whether they are sinking or sourcing. What does that mean?

A: Sinking (NPN) and sourcing (PNP) refers to the direction of the electrical current. An NPN switch sensor “sinks” current from the load through the sensor ground. The load is located between the positive voltage and the output of the switch sensor.

Conversely, a PNP switch sensor output becomes a “source” of the current to the load. The load is located between the switch output and the ground.