What Are Flow Controls?

The term flow control typically refers to an adjustable needle valve with an integral bypass, used to regulate the speed of an actuator. In this article, we will explore various types of flow controls to help you select the most suitable one for your operation.

1. Flow Control Using Fixed Orifice: This cost-effective option is tamper-proof and can serve as a simple restriction in a line or a factory-preset control with pressure compensation and a bypass.

2. Flow Control with Pressure and Temperature-Compensated Needle Valve: Equipped with check valves called bridge rectifiers, this type ensures fluid flows through the needle valve in a consistent direction, regardless of actuator movement.

3. Flow Control with Bypass (Throttle Valve): Meters flow in one direction while allowing free flow in the opposite direction.

4. Pressure and Temperature Compensated Flow Control: Utilize a pressure-compensated valve when precise speed control is essential, despite its higher cost compared to non-compensated valves.

There are three main types of flow control circuits: (i) Meter-in, (ii) Meter-out, and (iii) Bleed-off or bypass. Meter-in and meter-out are compatible with hydraulic systems, while pneumatics only use meter-in and meter-out.

Examples of Flow Control Circuits:

• Meter-in Flow-Control Circuit for a Cylinder: A bypass check valve forces fluid through an adjustable orifice before it enters the actuator.

• Pneumatic Meter-in Flow-Control Circuit with a Cylinder Extending: The pressure slowly builds until it generates enough force to start the piston moving, and then the expanding air accelerates cylinder movement.

• Meter-in Flow-Control Circuit for Overrunning Load with a Cylinder Extending: This circuit will not work with an overrunning load as the cylinder rod extends before a vacuum void forms and fills.

• Three-Speed Meter-in Flow-Control Circuit: Achieved using modular valves mounted on a bar manifold, it allows for different speeds based on valve configuration.

• Meter-out Flow-Control Circuit: Provides good control in pneumatic circuits and works well with air-operated devices as it restricts fluid leaving the cylinder to slow its movement.

• Bleed-Off or Bypass Flow-Control Circuit: Fine-tunes actuator speed and generates less heat compared to meter-in or meter-out systems.

• Meter-in Flow-Control Circuit with Pressure Switch for End-of-Stroke Indication: The pressure in the cylinder is just enough to move it and its attachments until it reaches the load.

• Meter-out Flow-Control Circuit with Pressure Switch for End-of-Stroke Indication: Oil flowing from the cylinder head-end port remains pressurized by the meter-out flow control.

• Meter-in Flow-Control Circuit for a Single-Acting Cylinder Extending: Suitable for both hydraulic and pneumatic cylinders with vertical single-acting extension.

• Pneumatic Meter-in Flow-Control Circuit as the Cylinder Contacts Second Equal Load: The movement may not be consistent in this case with a variable load on an air cylinder.

• Meter-out Flow-Control Circuit Controlling the Load on a Down-Acting Vertical Cylinder: Provides smooth and steady movement due to restricted fluid flow leaving the cylinder.

• Three-Speed Meter-out Flow-Control Circuit: Allows for different speeds based on valve configuration.

• Bleed-Off or Bypass Flow-Control Circuit: Works best in hydraulic circuits using fixed-volume pumps and only operates multiple actuators one at a time.

• Meter-In Flow-Control Circuit with Pressure-Compensated Pump: Ensures only the required flow is produced, minimizing wasted energy and heat.

• Meter-In Flow-Control Circuit with Variable-Volume Pump: Replaces flow controls and avoids heat generation by using all produced flow.

• Meter-In Flow-Control Circuit with Motor-Type Flow Divider: Preset speeds are achieved without changing hardware, offering various speeds by energizing different solenoids.

Selecting the appropriate flow control circuit depends on the specific requirements and characteristics of your application. Understanding these options will help optimize the performance of your hydraulic or pneumatic system.