Regulate/Control the Air Flow

As you know, pneumatic actuator speed is controlled by the air flow rate at the actuator. Air flow is controlled by a pressure difference: high pressure flows to low pressure. It would only make sense then that if we want to change the speed of an actuator, we need to regulate or control the air flow. To do this, we use a needle valve to control the flow.

If we have a small load and little frictional resistance, we can expect the speed of the actuator to be very fast. This is a problem if the application calls for a slower speed, so we must lower the speed of the actuator. A needle valve is often used to do this. The main function of the needle valve is to control the air flow rate by providing an additional frictional pressure drop in the system.

The following is a picture of the needle valve we will use in the labs.

The needle/flow control valve consists of a few components: 1) the body of the valve, 2) the adjustment knob, and 3) the adjustment screw. See the picture below.

Parker Hannifin Corporation. (1980). Industrial Pneumatic Technology. Parker Hannifin Corp. DOI: 1557690154

As you tighten the adjustment screw down, it restricts / causes frictional pressure drop. This decreases the flow and the speed of the actuator. Previously, we explained the ways to control the speed of the actuator, which are 1) increase load at the actuator, 2) increase system friction, and 3) decrease controlled pressure. Using a needle valve, we have increased system friction.

All pneumatic systems use some sort of flow control devices.

The picture below shows the schematic symbol of a needle valve/flow control valve.

Parker Hannifin Corporation. (1980). Industrial Pneumatic Technology. Parker Hannifin Corp. DOI: 1557690154

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