In various machines that use hydraulic systems, the hydraulic bypass valve can maintain stable system operation and protect hydraulic components. It is very important for equipment manufacturers and engineers to have a complete understanding of the working principle, types, applications, and selection methods of hydraulic bypass valves.
What is the Hydraulic Bypass Valve?
The hydraulic bypass valve is a valve installed in the hydraulic system to control pressure or flow. When the main circuit is blocked, the flow rate or pressure is abnormal, and it can provide a path for the fluid to bypass the obstructed component.
Why use the Hydraulic Bypass Valve？
Pressure Protection
The main function of a hydraulic bypass valve is to prevent excessive system pressure. When the fluid is obstructed, the valve is closed, or the load suddenly changes, the system pressure will rise rapidly, which may cause damage to the pipelines, seals or hydraulic pumps.
The bypass valve automatically opens when the pressure is more than the set value, directing a portion of the hydraulic oil to the standby channel or the return path, thereby reducing the system pressure and avoiding equipment damage.
Flow Regulation
When the system flow demand changes or the load changes, the hydraulic bypass valve can distribute excess flow to maintain stable system operation.
This is very important for hydraulic systems with frequent load changes or multiple actuators working simultaneously. It helps to reduce the pressure fluctuations.
Temperature Control
In the hydraulic oil cooling circuit, the hydraulic bypass valve can be adjusted according to pressure or temperature changes. When the environmental temperature is low, the hydraulic oil viscosity will increase.
The hydraulic bypass valve allows the oil to bypass components with high resistance such as the cooler, thereby reducing the starting load of the oil circuit. This helps the hydraulic oil complete the circulation quickly and reach a higher temperature.
This makes the hydraulic system start smoothly and enter normal working conditions gradually in low temperature environments. When the system temperature returns to normal, the bypass valve closes, and then the cooling process begins. It protects the cooling system and reduces equipment wear.
Maintain the Continuous System Operation
When a component in the hydraulic circuit is blocked or the flow rate is limited, the hydraulic bypass valve can provide an alternative path for hydraulic oil, allowing the system to continue working.
For example, when the filter is clogged or a control valve is closed, the hydraulic bypass valve opens. The hydraulic oil continues to flow around the blocked components, avoiding the system shut down or the actuators losing power.
This is very important for industrial equipment and construction machinery that need to operate continuously, and it can reduce losses caused by flow interruptions.
Protect the Hydraulic Components
When the system experiences abnormal pressure or flow changes, the hydraulic bypass valve guides hydraulic oil to reduce the impact on components such as hydraulic pumps, hydraulic filters, hydraulic coolers, and hydraulic actuators.
By reducing pressure fluctuations and flow surges, it is possible to extend the equipment service life and lower your maintenance costs.
Auxiliary Maintenance
Some hydraulic bypass valves can be controlled manually. When the main control valve of the device fails and needs maintenance, you can manually switch the oil circuit through the hydraulic bypass valve, allowing the actuator to complete simple reset or movement operations. This provides convenience for equipment maintenance.
How does the Hydraulic Bypass Valve Work?
The hydraulic bypass valve operates based on the interaction between the spring preload force and the hydraulic oil pressure. When the hydraulic system is operating normally, the valve core inside the hydraulic bypass valve remains in the closed state under the spring force.
The hydraulic oil will flow through the filter, cooler, actuator and other components along the designed path, completing the normal oil circulation.
When the pressure difference exceeds the standard, the oil circuit is blocked, and the oil temperature is too low in the system, it will cause an increase in oil flow resistance. The hydraulic pressure acting on the valve core will gradually increase and exceed the spring preload force, thereby pushing the valve core and opening the bypass channel.
At this point, the hydraulic oil does not pass through the components. It continues to flow through the bypass path formed by the hydraulic bypass valve.
When the system pressure and the oil flowability return to the normal range, the hydraulic pressure decreases. The valve core will close the bypass channel under the spring force, making the oil circuit return to the normal circulation.
Types of Hydraulic Bypass Valve
Pressure Hydraulic Bypass Valve
The pressure hydraulic bypass valve is one of the most common types of hydraulic bypass valves. It mainly controls the opening and closing of valves by detecting changes in system pressure.
When the pressure in the hydraulic system exceeds the set limit, the pressure hydraulic bypass valve automatically opens. It will direct some hydraulic oil to the bypass circuit or the return channel, thereby reducing the system pressure and preventing the device damage.
The pressure hydraulic bypass valves are commonly used for hydraulic pump protection, system overpressure protection, and load sudden change conditions to reduce pressure impact and keep stable system operation.
After the pressure returns to normal, the hydraulic bypass valve automatically closes under the spring force, and the system resumes its normal flow path.
Thermal Hydraulic Bypass Valve
The thermal hydraulic bypass valve operates according to changes in hydraulic oil temperature. It is commonly used in hydraulic oil cool systems or temperature sensitive circuits.
When the hydraulic oil temperature is low or the oil viscosity is high, the thermal hydraulic bypass valve opens. This allows the oil to bypass the cooler or high-resistance components, preventing the system pressure from rising and helping the oil quickly reach the operating temperature.
When the oil temperature rises to the set range, the thermal hydraulic bypass valve closes. Then, the hydraulic oil returns to flow through the cooler or main circuit.
This thermal hydraulic bypass valve usually uses temperature sensing elements for automatic adjustment and is widely used in construction machinery and industrial hydraulic systems.
Compound Hydraulic Bypass Valve
The compound hydraulic bypass valve integrates both pressure control and temperature control functions. It can automatically switch working modes according to different operating conditions.
When the system pressure is abnormal or the oil temperature is low, the compound hydraulic bypass valve will open the bypass channel to maintain the hydraulic system’s stable operation.
These compound hydraulic bypass valves are usually used in complex hydraulic systems or equipment with high stability requirements, such as large industrial hydraulic systems or heavy duty engineering equipment.
Oil Cooler Hydraulic Bypass Valve
The oil cooler hydraulic bypass valve is mainly used in the hydraulic oil cooling system. When the oil resistance is high or the oil temperature is low, the bypass valve opens, making some oil flow around the cooler.
This can prevent high pressure when high viscosity oil passes through the cooler. At the same time, during the system startup stage, it helps the oil temperature reach the normal operating range faster and reduces equipment wear.
Filter Hydraulic Bypass Valve
The filter hydraulic bypass valve is usually installed in the hydraulic filtration system. It is used to provide an alternative flow path when the filter element gets clogged or the flow is restricted.
When the pressure difference between the filter inlet and outlet reaches the set value, the filter hydraulic bypass valve will automatically open. This allows the hydraulic oil to continue flowing around the filter element, preventing insufficient oil supply from the hydraulic pump or system shutdown.
This filter hydraulic bypass valve is very important in the maintenance and protection of hydraulic systems. It can prevent operation interruption caused by filter blockage.
The Application of the Hydraulic Bypass Valve
Construction Machinery
Hydraulic bypass valves are widely used in the construction machinery hydraulic systems, such as excavators, loaders, cranes, and road rollers. These devices experience frequent changes in load during operation. When the actuator stops operating while the hydraulic pump continues to run, the system pressure will increase rapidly.
At this point, the hydraulic bypass valve automatically opens, allowing hydraulic oil to return to the oil tank or other circuits through the alternative channel, thereby avoiding system overpressure and maintaining stable equipment operation.
Industrial Machines and Automation Systems
In industrial equipment such as injection molding machines, CNC machines, forging machines, and in automated production systems, the hydraulic bypass valve is mainly used to maintain system operation accuracy and stability. These types of equipment have high requirements for the operational accuracy and stability of the hydraulic system.
When there is a sudden pressure change, flow fluctuation, or filter blockage during the production process, the hydraulic bypass valve can automatically guide hydraulic oil. This reduces the impact of pressure fluctuations on the operational accuracy of the actuator and avoids damage to hydraulic components.
Heavy Equipment
The working environments for mining machinery and heavy transportation equipment are usually very harsh. The hydraulic systems are easy to become contaminated by impurities and the loads often change.
The hydraulic bypass valve can respond to abnormal pressure in time and open the bypass circuit to release the pressure, protecting the high-pressure hydraulic components. It makes sure that the equipment can still operate stably under complex working conditions.
Applied to the Hydraulic Power Pack
In the hydraulic power pack, the hydraulic bypass valve is a commonly used safety protection component. Hydraulic power packs are widely used in automation equipment, lifting platforms, and small hydraulic tools.
The hydraulic bypass valves can handle working conditions such as system overpressure and local oil circuit blockage. It can make the pipeline layout simpler while improving the operational safety of the hydraulic power pack, making the system still have reliable pressure protection in a compact structure.
The Differences between the Hydraulic Bypass Valve and the Relief Valve
Function
The function of the hydraulic bypass valve is to provide an alternative flow path for the hydraulic oil. It is mostly used to bypass components such as filters and coolers. It can maintain an uninterrupted system oil supply and make sure continuous operation of the system under conditions such as oil blockage and low-temperature start-up.
The function of the relief valve is to limit the maximum pressure in the hydraulic system. When the system pressure exceeds the set value, the relief valve opens to guide the excess oil back to the oil tank or return channel, avoiding damage to components caused by pressure overload.
Installation Location
Hydraulic bypass valves are usually installed in parallel on both sides of components such as filters and coolers. It provides bypass channels for local circuits and does not directly regulate the main system pressure.
The relief valve is usually connected in parallel at the outlet of the hydraulic pump or at the end of the main oil circuit and directly connected to the main pressure circuit of the system.
Valve Opening Conditions
The opening of the hydraulic bypass valve is mainly determined by pressure difference, oil temperature or manual operation.
The relief valve operates based on the system pressure as the opening condition. When the system pressure reaches the preset value, the relief valve will open.
Impact on System Operation
After the hydraulic bypass valve is opened, the hydraulic oil is switched to the alternate flow path. However, the overall system pressure and operating status will not change, and the equipment can still work normally.
After the relief valve is opened, it will guide the high-pressure oil flow, keeping the system pressure stable at the set value and does not continue to rise. At this point, the main oil circuit pressure and flow rate will be adjusted.
How to Select a Hydraulic Relief Valve？
Clarify the Valve’s Purpose
Firstly, you need to know the specific purpose of the hydraulic bypass valve in your system to choose the proper type, such as the filter hydraulic bypass valve, the oil cooler hydraulic bypass valve and the thermal hydraulic bypass valve.
Consider the System Pressure
You need to determine the opening pressure and setting range of the hydraulic bypass valve based on system pressure, hydraulic pump rated pressure, circuit resistance, and equipment workload. At the same time, you also need to reserve a safety margin of 10% to 20% to handle the pressure shocks.
Consider the System Flow Rate
The bypass valve must be able to withstand the maximum flow rate of the system to avoid excessive pressure difference when the bypass is opened, which may affect system performance.
Consider Working Temperature and Medium Compatibility
You should choose the suitable valve body and seal material based on the working temperature range of the hydraulic system and the type of hydraulic oil.
For seals, you can choose nitrile rubber for mineral oil systems, and fluororubber for high temperature or synthetic oil. For valve body materials, you can choose cast iron or cast steel for ordinary industrial systems, and stainless steel for high-pressure or corrosive conditions.
FAQs
What would Happen if the Hydraulic Bypass Valve Gets Stuck?
If the hydraulic bypass valve is stuck in the closed state, the system may quickly generate high pressure when the flow is blocked or the load changes. This can cause excessive pressure on pipelines, seals, or pumps, resulting in equipment shutdown or component damage.
If the hydraulic bypass valve is stuck in the open state, the hydraulic oil will continue to bypass the main circuit, causing insufficient system pressure and slow actuator action.
Why does the Hydraulic Bypass Valve Produce Abnormal Noise?
Pressure fluctuations or unstable flow within the hydraulic system can cause abnormal noise from the hydraulic bypass valve. For example, when the air enters or oil flow is obstructed in the hydraulic system, it will cause the hydraulic bypass valve to frequently open and close, resulting in vibration and whistling sounds.
What causes the Hydraulic Bypass Valve to Become Stuck?
Metal debris and gum impurities in hydraulic oil entering the gap between the valve core and valve seat can directly cause blockage of the hydraulic bypass valve. A sudden change in system temperature causing thermal expansion and contraction of the valve core can also cause the hydraulic bypass valve to get stuck.
If there is a slight sticking, you can solve the problem by cleaning the valve core and replacing the clean hydraulic oil. If the hydraulic bypass valve core is severely worn or deformed, you need to replace the valve core.
Will the Long-Term Closure of the Hydraulic Bypass Valve Affect Its Service Life?
No. But there may be problems such as valve core sticking and reduced sensitivity. In a long-term stationary state, the sediment in the hydraulic oil may adhere to the valve core and valve seat. When the hydraulic bypass valve is reopened, there will be a delay in the action.
Seals may also undergo slight deformation under long-term static compression, leading to a decrease in sealing performance.
For devices that are in long-term standby mode, you can manually open or test the hydraulic bypass valve during regular maintenance to make sure smooth movement of the valve core.
In a Multi-Circuit Hydraulic System, should Hydraulic Bypass Valves be Installed Separately or Shared among Multiple Circuits?
In a multi-circuit hydraulic system, each independent circuit should be separately equipped with a hydraulic bypass valve. Sharing a hydraulic bypass valve can cause interference between the operating conditions of each circuit.
The pressure and flow settings of shared hydraulic bypass valves are difficult to meet all circuit requirements. Separate bypass valves can accurately protect each circuit. If one circuit is abnormal, it will not affect the normal operation of other circuits, and the system stability will be higher.
Will the Installation Direction of the Hydraulic Bypass Valve Affect Its Opening Pressure?
In most medium to high-pressure hydraulic systems, the spring preload of the hydraulic bypass valve is usually much greater than the valve core weight. Therefore, the installation direction has almost no effect on the hydraulic bypass valve opening pressure.
In low-pressure applications or when the valve core mass is large, gravity may have a slight impact on hydraulic bypass valves. For example, when the valve is installed vertically and the spool needs to open upwards, the additional gravitational resistance may cause the hydraulic bypass valve opening pressure to be slightly higher than the set value.
Final Thoughts
When there are pressure fluctuations, flow limitations or component failures, the hydraulic bypass valve can provide an alternative flow path. This allows the system to continue operating, reducing equipment shutdown and protecting components. If you need hydraulic bypass valves, please feel free to contact us.
