Rexroth Flow Control Valve Selection by Circuit Requirement

Selecting a Rexroth flow control valve starts with a simple question: what does the circuit need the oil flow to do? In many industrial hydraulic systems, flow determines actuator speed, but the correct valve depends on more than the required liters per minute. Load variation, pressure differential, direction of movement, mounting arrangement and the need for pressure compensation can all change the suitable solution.

A basic throttle valve may be sufficient where load conditions remain predictable. A pressure-compensated flow regulator becomes more relevant when actuator speed needs to remain comparatively stable as the load changes. Other circuits may require controlled flow in one direction and relatively free return flow in the other.

Buyers reviewing available hydraulic components can begin with Nabor's Bosch Rexroth hydraulic valve range and then narrow the requirement using the circuit conditions below.

Define What the Rexroth Flow Control Valve Must Control

Before choosing a valve series, identify the machine movement that needs speed control.

Typical requirements include:

• Controlling cylinder extension speed

• Controlling cylinder retraction speed

• Regulating hydraulic motor speed

• Maintaining a repeatable feed rate

• Slowing an actuator near part of its working cycle

• Balancing flow between different circuit branches

This distinction matters because the same nominal flow requirement can lead to different valve arrangements depending on where the valve is installed and how the load behaves.

Simple Throttle or Pressure-Compensated Flow Control?

One of the first decisions is whether the circuit can tolerate flow changing as pressure conditions change.

Simple throttle control

A simple throttle or restrictor changes the available flow area. It can be a practical solution for circuits where the load is relatively stable and extremely consistent actuator speed is not required.

The limitation is that flow through a restriction is influenced by the pressure difference across it. If the load changes significantly, actuator speed may also change.

Pressure-compensated flow control

A pressure-compensated flow regulator is designed to reduce the effect that changing pressure differential has on the metered flow within its specified operating range.

This makes pressure compensation more relevant for applications where:

• Actuator speed needs to remain relatively stable

• The machine load changes during the cycle

• Process feed rate affects product quality

• Repeatability matters more than basic manual adjustment

Bosch Rexroth's flow regulator technical documentation distinguishes simple flow restrictors from pressure-compensated flow regulators and provides a useful technical reference when defining this requirement.

Decide Between 2-Way and 3-Way Flow Regulation

Pressure compensation does not describe the complete circuit arrangement.

Buyers may also encounter two-way and three-way regulator concepts.

2-way flow regulator

A two-port pressure-compensated regulator meters the flow passing through the valve. Depending on the circuit design, excess pump flow may need to pass through another system path such as the main pressure relief arrangement.

This type of configuration can be suitable where the circuit architecture already manages excess flow appropriately.

3-way bypass flow regulator

A three-port regulator can meter the required controlled flow while diverting excess flow through a bypass path.

The practical choice therefore depends not only on actuator flow but also on what the hydraulic system should do with the remaining pump delivery.

When preparing an RFQ, indicate whether the circuit already provides a separate path for excess flow rather than requesting only “a 20 L/min flow control valve.”

Meter-In or Meter-Out?

The position of the flow control valve in relation to the actuator can change machine behavior significantly.

Meter-in control

Meter-in control restricts the flow entering the actuator.

It can work well where the hydraulic supply needs to determine actuator speed and the external load does not tend to drive the actuator faster than the incoming oil can control.

Meter-out control

Meter-out control restricts the oil leaving the actuator.

This arrangement is often considered when the load may tend to overrun or drive the actuator. Controlling the outgoing flow can help maintain back pressure and reduce uncontrolled acceleration.

The preferred arrangement depends on the actual machine mechanics, load direction and actuator behavior. It should not be selected from a catalogue name alone.

Check Whether Reverse Flow Must Be Free

Some applications need controlled movement in one direction but fast, relatively unrestricted movement in the opposite direction.

In that case, the circuit may use a flow control function combined with a reverse-flow check valve.

Typical examples include:

• Controlled cylinder feed with rapid return

• Controlled lowering followed by faster retraction

• Machine-tool feed circuits

• Material-handling movements with different forward and return speeds

The RFQ should therefore state whether flow must be controlled in both directions or only one direction.

Calculate the Flow Requirement From the Actuator, Not From the Valve Catalogue

Required flow should come from the machine operating requirement.

For a hydraulic cylinder, useful inputs include:

• Cylinder bore

• Rod diameter

• Required extension speed

• Required retraction speed

• Available pump flow

Cylinder extension and retraction may require different flow rates because the effective piston areas are different.

For a hydraulic motor, displacement and required rotational speed become relevant.

Do not automatically select the valve with the highest available flow rating. A valve should provide the required operating range while still allowing suitable adjustment and pressure-loss characteristics.

Normal Flow Matters as Much as Maximum Flow

Buyers often provide only the maximum pump flow.

That value is useful, but the normal controlled flow is also important.

Consider a machine where the pump can supply 80 L/min but the controlled feed movement normally requires only 8 to 15 L/min. A component chosen only because it can pass 80 L/min may not necessarily provide the most useful adjustment range for that working condition.

For an RFQ, record:

• Normal controlled flow

• Minimum useful flow

• Maximum required controlled flow

• Total pump delivery

Flow and Pressure Differential Need to Be Reviewed Together

A flow-control specification should not be reduced to a single L/min value.

Flow through a restriction depends on the pressure differential across the metering element. Pressure-compensated regulators are designed to manage this relationship more consistently, but they still operate within defined pressure and flow limits.

Provide:

• Normal system pressure

• Maximum system pressure

• Expected load pressure

• Required controlled flow

• Known pressure differential across the valve where available

This keeps the flow-control decision separate from a general valve-sizing exercise.

Consider Energy Loss and Oil Heating

Throttling hydraulic flow creates a pressure drop, and the hydraulic power lost across that restriction ultimately appears largely as heat.

For occasional or relatively low-power movements, this may be acceptable. In continuously operating, high-flow circuits, however, excessive throttling can increase oil temperature and reduce system efficiency.

Before selecting the valve, review:

• How much flow will be throttled

• Pressure difference across the valve

• How long the machine operates in the throttled condition

• Oil temperature limits

• Reservoir and cooling capacity

If substantial hydraulic power is continuously being converted into heat, the circuit architecture itself may deserve review rather than simply increasing the size of the flow control valve.

Mounting Style Should Match the Existing Circuit

Once the hydraulic function is defined, check how the valve will physically connect to the system.

Depending on the Rexroth product family and machine design, a flow-control function may be implemented using:

• In-line installation

• Subplate mounting

• Sandwich or modular construction

• Cartridge installation

• Manifold integration

For replacement work, record the existing connection arrangement, port sizes and mounting interface rather than assuming that a valve with the correct flow range will physically fit.

Check Fluid, Temperature and Contamination Conditions

Flow-control performance is also influenced by the hydraulic fluid and operating environment.

Record:

• Hydraulic fluid type

• Known viscosity range

• Fluid temperature

• Ambient temperature

• Filtration condition

• Seal material requirement

Fluid viscosity changes with temperature, and this can influence flow behavior, particularly in simple throttling arrangements.

Contamination can also affect small metering passages, so the cleanliness requirements for the selected valve should be checked against the existing hydraulic system.

When a Proportional Valve May Be More Appropriate

A manually adjusted or mechanically compensated flow regulator is not the only way to control actuator speed.

Some machines require the flow command to change continuously during the operating cycle under PLC or motion-controller control.

In that situation, a proportional directional valve may be more appropriate than a fixed flow-control setting.

For example, the  Rexroth R901382349 4WRPEH6 proportional directional valve combines proportional hydraulic control with integrated electronics and position feedback for applications requiring electronically controlled movement.

It should not be confused with a conventional flow regulator. The example is useful because it shows where the selection question changes from “How much flow should be mechanically regulated?” to “Does the machine need electronically variable motion control?”

Do Not Confuse Flow Control With Directional Control

A directional valve primarily determines which hydraulic paths are connected. A flow-control valve primarily regulates how much fluid passes through the controlled path.

Many machines need both functions.

If the unresolved question is spool symbol, neutral condition, switching positions or direction of actuator movement, see Nabor's          Rexroth directional control valve circuit selection guide        rather than trying to solve that problem through a flow regulator.

A Practical Rexroth Flow Control Valve Decision Guide

Rexroth Flow Control Valve RFQ Checklist

A useful RFQ should describe the circuit instead of providing only a target flow.

Questions to Ask Before Ordering a Rexroth Flow Control Valve

Should I choose a throttle valve or a pressure-compensated flow control valve?

It depends on the required speed stability and how much the circuit load changes. A simple restriction may be sufficient for less demanding conditions, while a pressure-compensated regulator is generally more appropriate when flow needs to remain comparatively stable despite changing pressure conditions.

What is the difference between meter-in and meter-out flow control?

Meter-in controls the oil entering the actuator. Meter-out controls oil leaving the actuator. The preferred arrangement depends on load direction and whether the actuator can be driven by the external load.

Why does the load matter when selecting a flow control valve?

Changing load changes pressure conditions in the hydraulic circuit. With a simple throttle arrangement, that can change the flow through the restriction and therefore the actuator speed.

Should I provide normal flow or maximum flow in an RFQ?

Provide both. Maximum flow helps establish capacity, while normal and minimum controlled flow help determine whether the proposed valve provides a useful operating and adjustment range.

Can I select a Rexroth flow control valve from flow rate alone?

Usually not. Pressure conditions, compensation requirement, load behavior, metering arrangement, mounting, fluid and temperature should also be considered.

When should I consider proportional flow control instead?

Proportional control becomes relevant when the machine needs the commanded flow or actuator speed to change electronically during the operating cycle rather than remain at a manually or mechanically adjusted setting.

Prepare the Circuit Requirement Before Comparing Models

Selecting a Rexroth flow control valve is primarily a circuit decision.

Determine the required actuator speed, normal and maximum flow, load behavior, pressure conditions and whether the circuit needs simple throttling, pressure compensation, one-way metering or bypass regulation. Then confirm mounting, hydraulic fluid and operating conditions before comparing individual valve configurations.

For a Nabor inquiry, provide the existing Rexroth part number where available together with the hydraulic schematic, flow requirement, pressure data and application description. If a particular valve is proposed, ask which operating conditions were confirmed and which values still depend on assumptions.