By: Justin Uhm
A pneumatic flow control valve, commonly known as a speed controller, is a hydraulic safety device that protects pneumatic components, such as a cylinder, from damage.
A pneumatic flow control valve includes orifices, which are used for controlling flow; these orifices can be used as a pressure-control device, and their intricate closed-loop electrohydraulic valves adjust depending on variations in pressure and temperature.
A speed controller opens a valve when air flows from the left to the right, establishing a free flow of air inside the valve. A speed controller equipped with a push-in function can regulate airflow to control the operational speed of a pneumatic circuit. A speed control valve that is designed to increase flow and function is shown in Figure 1.
Speed controllers are classified into pipe and cylinder direct type, based on the method of connection.
Circuit Application for a Speed Control Valve
Speed control valves, control the speed of a pneumatic cylinder and are classified into two types meter out and meter in.
Meter Outflow Control Valve
Meter out type control valves regulate the air exhaust from the actuator. Therefore, meter out valves are mostly used to control the speed of a cylinder. With a meter-out type, a speed controller is installed on the exit side of the cylinder so that it controls a cylinder’s drive by metering its discharge flow.
Meter In Flow Control Valve
A meter in valves, supply a small amount of airflow to the cylinder through the valve inside the speed controller. They are used on a single-acting actuator to regulate the air supply entering the device. If they are used on a double-acting actuator, they can create a friction motion. Therefore, the cylinder’s pressure is increased by compressed air in the in the cylinder and is discharged through the check valve inside the speed controller. Thus, the speed of the piston solely relies on the cylinder’s pressure increase. Meter-In type also restricts the flow to an actuator. A meter-in speed controller is ideal in applications in which a load offers a positive resistance to the airflow during a controlled stroke.
When to use a Flow Control Valve
When selecting a speed controller, you should consider the material, connection type, size, adjustment type, and configuration.
Material used in Speed Controllers
Composite fittings are most commonly used in general applications and have the broadest range of configurations while a glass nylon body reduces the fitting weight and cost.
Metal flow controls are designed for harsher environments in which fittings are exposed to abrasion, chemicals, or electric output. These flow controls feature an electroless, nickel a plated body, and a stainless-steel grab ring. Metal flow controls are mostly used in welding applications.
Connection Types Used
A flow connection fitting is available in NPT and metric threads. Thread sealant is pre-applied to NPT threads, while metric threads use an O-ring. A plug-in option is also available for push-in connections.
There are two types of adjustment options:
- A manual adjustment screw provides precise airflow control and regulation.
- A novelist model, which features a recessed adjustment screw. This model must be adjusted with a screwdriver, thus deterring unwanted tampering.
Configurations for Speed Control Valves
There are three types of configuration, 90-degree, swivel outlet, or inline models:
- 90-degree models are the most common.
- Swivel outlet models offer rotation on multiple axes for vertical or angled tube exit.
- Inline models can be used individually or stacked together. They are the best option when access to the actuator is difficult.
Pneumatic Flow Control Considerations
When selecting a flow control valve for a pneumatic pressure circuit, consider these points:
- A flow control should have the appropriate flow. A large capacity speed controller cannot control a small flow. When the speed controller is too large for the incoming air, the check valve inside the speed controller can vibrate.
- When controlling a small flow, you should establish product reliability by using a pneumatic pressure filter to minimize the effects of dust.
- Shorten the length of piping to minimize the volume of piping and improve the performance of the control. Also, choose an appropriate throttle valve for the flow.
- When connecting the speed controller, check the inlet and outlet of the speed controller to place it properly. If it is not installed properly, meter in and meter out will be reversed.
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