Incorrect Hydraulic Valve Sizing is one of the common causes of excessive pressure loss, increased hydraulic oil temperature, and reduced system efficiency in hydraulic systems. When a hydraulic valve is undersized and cannot meet the system’s required flow, hydraulic oil encounters greater resistance when passing through the valve’s internal flow passages. This resistance increases pressure loss and converts hydraulic energy that could otherwise be used to perform work into excess heat.

Therefore, correct hydraulic valve sizing is very important for equipment performance, energy efficiency, and long-term operational reliability. Understanding how hydraulic valve size affects hydraulic system pressure and temperature can help equipment manufacturers, maintenance engineers, and hydraulic product distributors avoid costly sizing errors.

Why Is Hydraulic Valve Sizing Important?

Hydraulic valves are mainly used to control the direction, pressure, and flow of hydraulic oil. Each hydraulic valve has a specific flow and pressure operating range.

Even if a hydraulic valve has a high rated working pressure, it does not mean it is suitable for a hydraulic system requiring a larger flow.

For example, although a certain solenoid directional valve can withstand a high system pressure, when the actual flow approaches the upper limit of its operating range, it may still produce a large pressure loss.

Therefore, the correct hydraulic valve specification should be selected according to the required flow, pressure loss characteristics, working conditions, and hydraulic circuit design.

Reasonable hydraulic valve selection helps maintain efficient flow of hydraulic oil while avoiding unnecessary flow resistance.

How Does an Undersized Hydraulic Valve Cause Pressure Loss?

Pressure loss occurs when hydraulic oil flows through restrictive passages inside the valve.

These restrictive passages may include spool flow passages, internal oil passages, control openings, and connection ports.

When the hydraulic valve is undersized relative to the system’s required flow, the velocity of hydraulic oil passing through the internal flow passages increases.

As flow demand increases, the pressure difference between the valve inlet and outlet usually also increases.

This may cause the following problems:

• The hydraulic pump needs to provide higher output pressure
• In some hydraulic circuits, the effective pressure available to the actuator is reduced
• Hydraulic system energy consumption increases
• Hydraulic cylinder movement speed decreases or operation becomes unstable
• More heat is generated in the hydraulic oil

For solenoid directional valves, pressure loss needs to be evaluated according to the actual working oil paths, such as the flow paths from P to A and from B to T.

Even with the same valve body specification, different spool functions may produce different pressure losses.

Therefore, the actual hydraulic performance cannot be accurately judged only by the nominal diameter of the hydraulic valve.

Why Does Excessive Pressure Loss Generate Heat?

Hydraulic systems transmit energy through hydraulic oil under a certain pressure.

When hydraulic oil flows through narrow passages inside a valve, part of the hydraulic energy is consumed rather than used to perform effective mechanical work.

This part of the energy is mainly converted into heat.

The power loss generated when hydraulic oil passes through a restrictive passage can be estimated using the following formula:

Power loss (kW) = pressure loss (bar) × flow (L/min) ÷ 600

For example, assume a hydraulic valve operates under the following conditions:

• Hydraulic oil flow: 80 L/min
• Valve pressure loss: 15 bar
• Calculated power loss: 2 kW

This means that when the above operating conditions are continuously maintained, approximately 2 kW of hydraulic power is consumed and converted into heat.

If correct sizing reduces the pressure loss at the same flow to 5 bar, the power loss will drop to approximately 0.67 kW.

The difference between the two is approximately 1.33 kW, representing the reduction in hydraulic power loss under that operating condition.

The actual temperature of a hydraulic system also depends on the equipment working cycle, hydraulic oil volume, cooling capacity, and other heat sources.

Common Symptoms of Incorrect Hydraulic Valve Sizing

Incorrect hydraulic valve sizing may cause various abnormal equipment operations.

1. Excessive Hydraulic Oil Temperature

If the hydraulic valve is undersized, large flow resistance may be generated during continuous equipment operation.

The resulting energy loss increases the heat in the hydraulic oil.

When the cooling capacity of the hydraulic system is insufficient to remove this heat, the hydraulic oil temperature may exceed the recommended operating range.

Excessively high hydraulic oil temperature may reduce lubrication performance and accelerate the aging of seals and other hydraulic components.

2. Slower Hydraulic Cylinder Movement Speed

A hydraulic cylinder requires sufficient hydraulic oil flow to achieve the expected operating speed.

If the hydraulic valve produces excessive pressure loss, the hydraulic system may be unable to maintain the required flow under load conditions.

This may cause the extension or retraction speed of the hydraulic cylinder to decrease, especially when the hydraulic pump has already reached its pressure or power limit.

3. Increased Energy Consumption

When a hydraulic valve produces unnecessary flow resistance, the hydraulic pump may need to provide higher pressure to maintain normal operation of the actuator.

This increases the power demand of the hydraulic system and raises equipment operating costs.

For industrial equipment that needs continuous operation or frequent operation, this effect is usually more obvious.

4. Unstable Hydraulic System Operation

Excessive pressure loss may cause unstable system operation, especially when hydraulic pump flow is insufficient, valve control characteristics do not match, or the load changes continuously.

Operators may find that hydraulic cylinder movement speed is uneven, actions are inconsistent, or equipment working efficiency decreases.

However, these phenomena may also be caused by other hydraulic faults, so they cannot be directly judged as hydraulic valve sizing problems without inspection.

5. Increased Wear of Hydraulic Components

Additional heat and operating load may accelerate the degradation of hydraulic oil performance, aging of seals, and wear of hydraulic components.

After long-term operation, these problems may increase equipment maintenance requirements and shorten the service life of hydraulic equipment.

Difference Between Hydraulic Valve Flow Capacity and Pressure Rating

A common mistake in hydraulic valve selection is confusing pressure rating with flow capacity.

In fact, these two parameters represent different performance indicators.

Pressure Rating

Pressure rating indicates the maximum hydraulic pressure that the hydraulic valve can withstand under specified conditions.

Flow Capacity

Flow capacity indicates the hydraulic oil flow that the hydraulic valve allows to pass under specified working conditions.

Pressure Drop

Pressure drop indicates the inlet-to-outlet pressure difference required for hydraulic oil to pass through a specific flow path of the valve.

For example, a hydraulic valve with a rated working pressure of 315 bar does not mean that it can maintain ideal performance under all operating conditions below the catalog maximum flow.

The actual working flow should be evaluated together with the pressure loss characteristic curves provided by the manufacturer.

System designers should also consider factors such as hydraulic oil viscosity, spool function, and working temperature.

NG6 vs. NG10: Why Is Hydraulic Valve Sizing Important?

NG6 and NG10 solenoid directional valves are widely used in industrial hydraulic systems.

Generally, the 4WE6 series uses the NG6 mounting interface, while the 4WE10 series uses the NG10 mounting interface.

These two types of hydraulic valves are suitable for different flow requirements.

NG6 Solenoid Directional Valves

NG6 hydraulic valves are usually used in compact hydraulic systems, machine tool equipment, and industrial machinery with medium flow requirements.

This series has smaller mounting dimensions and is suitable for many common hydraulic control circuits.

However, if an NG6 hydraulic valve is used in a system with excessive flow demand, significant pressure loss may occur.

NG10 Solenoid Directional Valves

NG10 hydraulic valves usually have larger internal flow passages and are suitable for hydraulic systems with higher flow requirements.

Under appropriate application conditions, NG10 hydraulic valves may produce lower pressure loss at the same flow than smaller-sized hydraulic valves.

However, the actual pressure loss still depends on valve structure, spool type, and working conditions.

In addition, NG6 and NG10 hydraulic valves use different mounting interfaces.

If an existing NG6 hydraulic valve is replaced with an NG10 model, the mounting subplate, hydraulic valve block, or related pipeline connections may also need to be replaced.

Therefore, correct hydraulic valve selection should be based on actual flow and pressure loss requirements, not solely on nominal diameter.

Can Oversized Hydraulic Valves Also Cause Problems?

Although undersized hydraulic valves may cause pressure loss and temperature rise, choosing an oversized hydraulic valve is not necessarily the best solution.

An oversized hydraulic valve may increase equipment procurement costs and occupy more installation space.

In proportional flow control applications, if the valve’s rated flow is significantly higher than the actual requirement, the effective control resolution in the low-flow range may decrease.

If the valve does not match the actual application, precise flow regulation may become more difficult.

Therefore, hydraulic valve selection should comprehensively consider flow capacity, pressure loss, control accuracy, installation requirements, and the operating efficiency of the entire hydraulic system.

How to Choose the Correct Hydraulic Valve Size?

Selecting a suitable hydraulic valve requires a comprehensive evaluation of multiple technical factors.

1. Confirm the Required Flow

First determine the hydraulic oil flow actually required by the hydraulic actuator.

For a hydraulic cylinder, consider the expected operating speed and effective piston area.

For a hydraulic motor, consider the operating speed and displacement.

At the same time, check the system’s normal working flow and peak flow.

2. Review Pressure Loss Characteristic Curves

Use the technical data provided by the manufacturer to evaluate the pressure loss of the hydraulic valve at the expected flow.

For solenoid directional valves, check the corresponding spool function and working oil paths.

Do not select based only on the maximum flow marked on the product.

3. Consider Hydraulic Oil Viscosity

Hydraulic oil viscosity affects the resistance generated when oil flows inside hydraulic valves, hoses, and pipelines.

When viscosity is higher, especially during cold startup of the equipment, pressure loss may increase.

Therefore, hydraulic valve selection should consider the operating temperature and viscosity range of the hydraulic oil.

4. Evaluate Working Pressure

Confirm the working pressure required by the hydraulic system and the maximum pressure the hydraulic valve may withstand.

The rated pressure of the selected hydraulic valve must meet the system requirements.

At the same time, rated pressure and flow capacity should be evaluated as two independent parameters.

5. Check the Equipment Working Cycle

The heat load generated by a hydraulic valve passing a large flow for a short time may differ from that generated during long-term continuous operation.

For continuously operating hydraulic equipment, special attention should be paid to pressure loss and heat generation.

6. Confirm Installation Compatibility

Check the hydraulic valve’s mounting interface, port arrangement, electrical requirements, and spool function.

When replacing an existing hydraulic valve, the new model must meet the control requirements of the original hydraulic circuit.

Even if the mechanical mounting dimensions are the same, it does not necessarily mean that the two hydraulic valves have the same hydraulic performance.

How to Reduce Pressure Loss and Hydraulic Oil Overheating?

If excessive pressure loss is suspected in a hydraulic system, inspection should be carried out first before deciding whether to replace hydraulic components.

It is recommended to focus on checking the following:

• Measure the pressure before and after the suspected faulty valve under representative working conditions.
• Confirm the actual hydraulic system flow, rather than relying only on the hydraulic pump nameplate parameters.
• Compare the actually measured pressure loss with the characteristic curves provided by the manufacturer.
• Check filters, hoses, fittings, and hydraulic valve blocks for additional flow resistance.
• Check hydraulic oil viscosity and working temperature.
• Verify the spool function and oil circuit connections of the solenoid directional valve.
• Check the relief valve setting and whether there is unnecessary bypass flow.
• Evaluate whether a hydraulic valve with different flow characteristics needs to be selected.

In some applications, replacing with a larger-sized hydraulic valve can indeed reduce pressure loss, but this is not the solution to all problems.

For example, hydraulic oil overheating may also be caused by incorrect relief valve adjustment, blocked return lines, hydraulic pump wear, or insufficient cooling system capacity.

Therefore, a comprehensive inspection of the entire hydraulic circuit helps accurately identify the source of energy loss.

XYIYEYA Hydraulic Valve Solutions

XYIYEYA provides hydraulic valves and related hydraulic components suitable for industrial machinery, hydraulic power units, and equipment maintenance applications.

We assist customers in identifying and selecting suitable hydraulic valve models according to their flow requirements, working pressure, mounting dimensions, and control functions.

Recommended Hydraulic Products

XYIYEYA provides a variety of commonly used hydraulic valve series to meet different flow and pressure control requirements.

• 4WE6 Series Solenoid Directional Valves: Use the NG6 mounting interface, feature a compact structure, and are suitable for industrial hydraulic systems whose flow requirements are within their performance range.
• 4WE10 Series Solenoid Directional Valves: Use the NG10 mounting interface and are generally suitable for hydraulic control circuits requiring larger flow.
• 4WRA / 4WREE Series Proportional Directional Valves: Suitable for industrial equipment requiring proportional control of hydraulic oil flow and actuator movement.
• Z2FS Series Flow Control Valves: Modular throttle check valves that can be used to regulate hydraulic oil flow and control the operating speed of actuators.
• DB / DBW Series Relief Valves: Used for hydraulic system pressure regulation, overload protection, and, in applicable models, electrically controlled unloading.
• 2FRM Series Flow Control Valves: Used to regulate and control hydraulic oil flow in appropriate industrial hydraulic applications.

These product series provide multiple options for hydraulic system design, equipment maintenance, and replacement parts procurement.

During actual selection, the appropriate model should be determined according to the hydraulic circuit requirements and the specific working characteristics of the product.

Hydraulic Component Procurement Support

XYIYEYA provides product selection, model identification, and replacement component procurement support for hydraulic equipment manufacturers, maintenance service providers, and industrial hydraulic product distributors.

Our product range includes hydraulic directional valves, pressure control valves, flow control valves, proportional valves, hydraulic pumps, and related hydraulic accessories.

Whether you are selecting valves for a new hydraulic system or need to replace existing hydraulic valves, we can assist in confirming technical parameters and evaluating product compatibility.

Welcome to contact XYIYEYA for available models, product technical data, prices, and competitive product quotations.

Conclusion

Incorrect hydraulic valve sizing may cause excessive pressure loss, increased hydraulic oil temperature, and reduced operating efficiency of the entire hydraulic system.

If the hydraulic valve specification cannot meet the actual flow requirement, it may cause unnecessary energy consumption, unstable equipment operation, and increased maintenance requirements.

However, choosing the largest hydraulic valve is not necessarily the best solution. Correct hydraulic valve selection requires comprehensive consideration of flow capacity, pressure loss characteristics, actual working conditions, and hydraulic control requirements.

XYIYEYA provides a variety of hydraulic control valves to meet the needs of different industrial applications. Welcome to contact us for hydraulic valve selection support, product model recommendations, and competitive quotations.