A counterbalance valve is a hydraulic component that operates with an overriding or suspended load.
Their role is to generate back pressure within the return line of the actuator, ensuring the retention of control over the load is maintained.
Functions of Counterbalance Valve
Counterbalance valves serve several functions in hydraulic systems, which include;
- Holding Load – A counterbalance valve incorporates both the features of a reverse free-flow check valve and a pilot-operated relief valve. In its role as a load-holding valve within a hydraulic cylinder system, the free-flow check permits unrestricted oil flow into the cylinder for raising the load.
- Controlled Lowering of Load – To lower the load efficiently, the control valve is shifted accordingly to prevent the load from dropping quickly.
- Assist in Managing Variable or High Back Pressure – Relief valves that are completely balanced play a role in stabilizing the hydraulic system that experiences changes in back pressure.
- Ensures Load Safety especially when the Line Break – Counterbalance valves attached to the valve actuators help in controlling pressure induced by loads and impacts. This ensures load stability, handling potential hose failures, and preventing damage to your equipment.
Counterbalance Valve Symbol
The symbol for the counterbalance valve may vary slightly depending on the conventions or standards used in a particular system or industry. In most cases, it is a square box with an arrow inside pointing against the flow direction of the fluid as shown;
Where to use Counterbalance Valves in Hydraulic System
Counterbalance valve plays an important role in hydraulic systems, they are usually used in areas of load holding, protection against overrunning load, and controlled lowering of loads are essential.
Some of the application areas of counterbalance valves include;
- Used in construction machinery such as cranes and excavators.
- In the conveyor system where loads are required to be lifted and controlled lowering of the load.
- In agricultural machinery such as tractors.
- In manufacturing processes such as stamping machines and metal forming machines.
- Used in elevator systems
- Used as an emergency brake system especially in cases of hydraulic system failure to quickly stop the descent of a load.
How Counterbalance Valves Working Principle
A counterbalance valve combines both the features of a reverse free-flow check valve and a pilot-operated relief valve.
In its application as a load control and load-holding valve within the hydraulic cylinder system, the free-flow check permits unrestricted oil flow into the cylinder for raising the load.
Upon shifting the control valve to the neutral position, the pressure induced by the load forces the check valve to close. As long as this pressure remains below the relief function setting, the load remains stationary until the control valve is shifted to lower it.
Subsequently, the pressure on the opposite side of the cylinder along with the pressure induced by the load, acts on the pilot port, exceeding the relief setting.
Shifting the control valve back to neutral leads to the loss of pilot pressure, causing the relief valve to close once again and securely maintaining the load in its position.
Moreover, a counterbalance valve exhibits a modulating behavior influenced by both the load pressure and pilot pressure, resulting in an inverse pilot ratio. Essentially, lighter loads demand increased pilot pressure, whereas heavier loads require less pilot pressure.
In routine operations, the relief function’s adjustable spring force is surpassed by a combination of pilot pressure and load-induced pressure. The modulation is such that as the load-induced pressure rises, the need for pilot pressure decreases, and vice versa.
This modulation ensures the counterbalance valve maintains seamless operational control across a dynamic load curve.
Counterbalance Vs. Pilot-operated Check Valves
To ensure safe operation of the hydraulic system, a thorough understanding of the operational distinctions between pilot-operated check valves and counterbalance valves is essential.
Both pilot-operated check valves and counterbalance valves serve the purpose of locking fluid in a cylinder to prevent drifting. Nevertheless, it’s crucial to note that a pilot-operated check valve lacks the capability to manage an overrunning load.
In situations where uncontrolled movement may arise due to an overrunning load, the use of a counterbalance valve is recommended.
Additionally, a counterbalance valve offers smoother operation in managing the descent of a load while pilot-operated check valves provide a leak-free seal.
The distinction comes up during the opening of the pilot check valve, the load has the potential to lead cylinder flow ahead of pump delivery leading to loss of the pilot signal and prompting the valve to close abruptly.
How to Set up and Troubleshoot Counterbalance Valves
To appropriately set the counterbalance valve, you need to adjust its spring to the maximum setting possible to elevate the load.
In many counterbalance valves, this adjustment is achieved by rotating in an anticlockwise direction to enhance or increase the spring force.
Subsequently, slowly rotate the adjustment in the opposite direction but this should be done with caution by ensuring there is nothing of value underneath the load.
Once the load begins a slow and gradual descent, re-adjust the setting in the initial direction until the drifting stops. Proceed to rotate the adjustment by a quarter of a turn in the same direction and securely fasten the lock nut.
When a counterbalance valve malfunctions, it becomes stuck in the open position causing the load to slowly descend. When such cases occur, the most efficient, cost-effective, and easiest approach is to check on the counterbalance valve.
The presence of contaminants can lead to the internal check valve or spool becoming lodged in the open position. Therefore, a proper inspection should be done of the internal check valves to detect such contaminants.
Once this is confirmed, proceed to remove the valve and conduct further inspection for any issues such as debris or broken springs. Remember, before removal of the valve, exercise caution by lowering the load to the ground and also ensure that the pressure of the hydraulic line has been safely blended down to 0 psig.
Choosing Counterbalance Valves for Hydraulic Systems
In selecting the perfect counterbalance valves, you should consider a range of factors for optimal performance and they include;
· Pilot Ratio
A major role of the pilot ratio is to regulate the pressure range required to transition the valve from a closed position to a fully opened one.
When you lower the pilot ratio, it provides better motion control while a higher ratio emphasizes efficiency. Therefore, it is important to choose the pilot ratio that will align with the system’s needs.
· Load Characteristics
Different loads may have different counterbalance valve characteristics.
Evaluating characteristics such as load weight, direction, and speed will not only help in ensuring the valve is compatible with specific loads but also contribute to the efficiency and safety of the system.
· Cylinder Ratio and Size
To ensure compatibility and optimal performance of the hydraulic system, the size and the ratio of the hydraulic cylinder should match the counterbalance valve characteristics.
· Application Requirements
Different applications may require distinct counterbalance valves. This is due to variations in load types, load characteristics, and desired speed of movement.
Therefore, it is essential to select a valve that will effectively meet the demands posed by the application, promoting the safety and optimal performance of the system.
· Pressure of Hydraulic System
The maximum pressure of the system should be known to ensure that the counterbalance chosen can manage the operational conditions without interference with safety and efficiency.
· Adjustability and Valve Setting
You should choose a counterbalance valve with adjustable settings which can adapt to variations in loads. Ensure there is ease of adjustment and compatibility with the system’s requirements for optimal performance.
· Location in Hydraulic System
Proper placement of the counterbalance valve in a hydraulic system enhances its role in load control by reacting swiftly to changes in load conditions.
Setting Counterbalance Valves in Hydraulic System
Counterbalance valves are commonly adjusted to 1.3 times the maximum load pressure to ensure proper resetting even under the most demanding load conditions.
In some cases, manufacturers may recommend a setting of 1.5 times the maximum load pressure, particularly if that value is below 2000 PSI.
Counterbalance valves come in a range of pilot ratios.
Opting for lower pilot ratios enhances motion control and stability, although this may come at the cost of efficiency and potential heat generation. Conversely, higher pilot ratios offer improved efficiency.
Consequently, for load-holding cylinder applications, pilot ratios around 3:1 or 4.5:1. You will find this configuration to be common. They are commonly preferred since they offer a suitable balance between performance and efficiency.
Irrespective of the pilot ratio chosen, determining the pilot pressure involves taking into consideration factors such as cylinder ratio, pilot ratio, location of the counterbalance valve, and load pressure.
Counterbalance valves are crucial in offering versatile solutions for controlling the movement of loads and ensuring controlled descent of load. Their versatility enhances efficiency and safety across diverse industrial applications.