What is a flow control valve?

Flow control valves are used in pneumatic systems to regulate the flow rate of compressed air. By controlling the flow rate, the speed of the pneumatic cylinder can also be regulated directly. In addition, a good throttling valve contributes to reducing wear due to a lower kinetic load. Moreover, the control valves also support a more steady and thus reliable movement. The latter has to do with the fact that if the speed is unthrottled, the velocity can fluctuate. This in turn can lead to a stick/slip effect and thus to a faltering motion.

Different types of flow control valves

Flow control valves are also referred to more generally as flow regulators or flow controllers. They are available in different versions. This blog focuses on the banjo shaped flow control valve with in-built check valve. This valve is by far the most commonly used. And not without reason. On the one hand, this flow regulator is popular because of its functionality and on the other hand because of its easy assembly. This type of flow control valve is mounted directly on the cylinder, allowing the actuator speed to be set on site. In addition, the angled flow regulator with check valve is very easy to operate from the side.

Function of a throttling or flow control valve

According to the dictionary, throttling means slowing down or dampening. A throttling valve thus slows down the speed of the air flow. This is done by adjusting the height of the throttling needle over its nozzle means of a control knob, thereby varying the flow rate. When the flowis lower, the corresponding cylinder chamber will fill less quickly, which in turn translates into a slower cylinder movement.

Flow meter controls speed independently

For most applications, it is desirable to be able to control the speed in each direction independently. Throttling incoming air on a double-acting cylinder causes an unstable motion profile.

In order to be able to control both stroke directions independently, throttling valves with an integrated non-return valve can be used. In these flow regulators, the compressed air is thus throttled in one direction only (flow from port 1 to 2) while in the other direction it can flow without restriction (port 2 to 1). This is achieved by means of a diaphragm that is self-closing in the controlled flow direction.

Pressurising and exhausting with throttle valves

Since throttle valves with a non-return valve regulate in one direction, we have two different types:

  • Throttling valves which throttle the exhaust air (exhausting)
  • Throttling valves which throttle the supply air (pressurising)

Throttling valve on the exhaustside

For most cylinder applications, it is desirable to control the speed on the exhaust (venting) side. The advantage of this is that the venting chamber continuously exerts a counter pressure on the other chamber, which is filled with compressed air without restriction. In this way, a controlled movement is created in which the stick/slip effect is avoided.

The blue control knob and the type designation LE (exhaust) indicate that Festo VFOE series throttling valves throttle the exhaust air.

Flow control valve based on pressurisation

Flow control valves with pressurisationcontrol are mainly used for single-acting cylinders. Here, the return stroke is produced mechanically (usually a spring). These types of throttling valves can also be used for smaller and short-stroke cylinders with a small swept volume. Here, there is not enough volume available for the 'air cushion' effect.

The light blue control knob and the type designation LS (Supply) identify the Festo VFOE series that throttle the supply air. The LS types can be combined with cylinder diameters < 16 mm and stroke lengths < 25 mm.

Product range throttling valves

The Festo range includes various types of angled flow control valves. All of these flow regulators can be mounted directly on the cylinder.

VFOE throttle valve

The standard flow control valve and part of our core program is the VFOE. Its lightweight and compact design makes this flow controller very suitable for applications with little installation space. In addition, the VFOE has a wide range of connection sizes and is available in both LS and LE types. For larger projects, the VFOE valves can also be ordered in volume packaging at a more competitive price.

GRLA throttling valve

Due to its metal housing, the GRLA is a robust flow regulator available in various versions. The RS version is equipped with a control screw that can be secured with an additional nut. The B version has a threaded connection instead of a hose connection. The MF version is somewhat larger in volume and therefore suitable for a higher maximum flow capacity.

VFOH & CRGRLA Throttling Valves

For applications in aggressive environments, the all-steel VFOH throttling valves with push-in coupling are the best choice. These flow regulators have a higher resistance against cleaning agents and other strong acids and bases. For extreme situations, such as an ATEX environment, the all stainless steel CRGRLA is the optimal solution. This version has the highest corrosion resistance in the portfolio.

July 2022