Utilization of hydraulic systems in several diverse applications has been on the increase over the past few years. These systems are fitted with hydraulic valves that also increase the service life of the system.
What is a Hydraulic Check Valve
A hydraulic check valve is a device installed into the system as a control measure. It plays a very important role in ensuring that all the systems function properly without risking damage. The valve’s main function is to act as a barricade and therefore prevent any fluids from flowing backwards.
Decrease in pressure levels in the system often results in backflow of fluid, this device stops that flow even under low-pressure levels.
This fluid may pick up contaminants as it flows through the system and therefore the backflow is considered contaminated. Therefore, preventing this backflow is also a way of securing the system from potential damage caused by contaminants.
Hydraulic Check Valve Symbols
Hydraulic check valves function differently depending on the mechanism it is designed with. There are therefore different symbols that are used to represent the check valve.
The first symbol is A. This represents a check valve without a spring this valve relies on gravity to prevent any backflow of liquids.
Another hydraulic check valve is the spring check valve. This type of valve has a spring that helps it perform its function as opposed to gravity. It is represented by the symbol B
The next symbol is used to represent a pilot to close check valves. This symbol represented by a broken line above the ball is the pilot line. Pressure is applied to prevent backflow
The last symbol is used to represent a pilot-controlled check valve. It also has pilot lines that can be used to prevent backflow but it can also be lifted to allow fluid to flow back.
The last symbol is used to represent the shuttle valve. It is commonly used in load-sensing systems.
Importance of Check Valves in Hydraulic Systems
There are many advantages to using hydraulic check valves. They include;
- Hydraulic check valves can be used as a means of adjusting pressure. It does this by blocking pressure spikes that are a result of pumps remaining operational despite the passage being blocked.
- They prevent the system from getting damaged by preventing fluid from escaping the pump when the system is not operating.
- The hydraulic valves prevent backspin. This occurs when a system has an accumulator which helps keep liquid pressurized.
- It is a valuable tool for systems with multiple pumps. The hydraulic check valves stop fluid from an operational pump from flowing back into a dormant pump.
Best Materials for Hydraulic Check Valve Construction
Different types of materials are used to forge hydraulic check valves. The best materials may vary depending on the application of the check valve as well as the environment in which it is going to be used. These materials include;
- Aluminum is advisable for systems with low pressure.
- Although brass is not popularly used it can be used in a corrosive environment
- Cast iron is recommended for high pressured systems
- Stainless steel is the best material to use for corrosive and high-temperature applications.
Types of Hydraulic Check Valves
- Ball Valves: This is the most commonly used type of hydraulic check valve. It uses a ball that applies pressure from gravity to prevent fluid from flowing backward.
- Piston Check Valve: A piston check valve uses a piston that is weighed to stop the fluids from going back to the reservoir.
- Spring-loaded Check Valve: The spring-loaded check valve uses a combination of a ball and a spring. The tension applied to the spring helps to control the liquid blocking its ability to go back into the system.
- Modular Hydraulic Check Valves: This check valve uses automatic transmissions to control the flow of fluid. It does this by controlling the pressure of the fluid.
- Hydraulic Cartridge Check Valves; These control the internal pressure and the direction of the flow of the fluid as well as the internal pressure of the hydraulic systems.
- Hydraulic inline check valve: In-line valves function by controlling the pressure in the system. Controlling pressure allows them to also control the direction of the flow of fluids preventing them from flowing back.
- Hydraulic pilot check valve: It is equipped with an external pilot line that is used to operate the check valve. Pressure is applied to the external line preventing the fluid from flowing back.
- Double pilot-operated check valve hydraulic: This type of check valve allows for bi-directional control of the fluid transportation. The direction of flow can be controlled using a pilot pressure signal located on the outside.
Parts of Hydraulic Valves
The parts of hydraulic valves differ according to the type of hydraulic valve you have.
Despite the fact that they all perform the same function, they achieve this using different mechanisms. The main parts of a hydraulic valve include the body of the valve, a seat with a linked plate, and a cover. Additional features are what bring about the different types of hydraulic valves. These additional features include balls, springs, and pilot lines among others.
How Check Valves in Hydraulic Systems Work
Hydraulic valves have an easy method of operation. These valves’ main function is to prevent fluid from flowing back into the main supply.
Depending on the type of hydraulic check valve you have this function will be fulfilled in several ways. The valve blocks passage using balls, springs, or by controlling the internal pressure which in turn controls the direction of the flow of fluids.
How to Choose Check Valves for Hydraulic Systems
There are several factors that you should take into consideration when selecting a check valve. These factors mostly revolve around the application that is intended for the hydraulic system and by extension the check valve. The factors include
- The method of operating the check valve and whether it will be internally or externally controlled.
- The working principle of the check valve in terms of how they prevent backflow. It could be using pressure or a physical barricade.
- It is also important to consider if you want one-direction control or a two-way controlling method.
- The material used to design the valve.
- You should select a material that will not be easily damaged from your applications.
- The location in the hydraulic system where the check valve will be installed.
Causes of Hydraulic Check Valve Failure & Possible Solutions
There are a few setbacks that you are likely to experience when using a hydraulic check valve. The most commonly faced challenges include;
- Check valve blockage caused by an increase in the amount of debris in the system. This problem often results due to poor maintenance practices. Failure to regularly clean the system may allow debris to pile causing the valve to remain open or remain closed. This problem can easily be rectified by deep cleaning the system to remove the debris. It should be followed with regular maintenance to prevent the build-up from re-occurring.
- Low pressure in the system may result in inconsistent fluid flow. Low pressure will cause the check valve to open and close at regular intervals. This unnecessary movement will lead to the wear of the check valve. The malfunction will cause irregular flows and fluctuations in the valve. Lubricating the moving will reduce the rate of wear and tear. Including accumulators in your hydraulic systems will help maintain pressure in the system.
- Poor installation of the check valve often results in reverse flow. If it is not fitted properly then the valve cannot also perform its function of preventing liquid from flowing. Poor fittings and installation are the cause of reverse flow, then it can be rectified by removing the check valve and reinstalling it properly. When you are having trouble with installation, it is better to seek the services of a professional to ensure that it is done properly.
- High temperatures may lead to a shorter service life of your check valve. Subjecting the check valve to consistently high temperatures may cause it to get damaged much faster. It is therefore important that when using high-temperature applications you should get a check valve with a heat-resistant material such as stainless steel to ensure you get a longer service life. When the check valve eventually gets worn you can replace it with new ones.
Hydraulic Check Valve Testing
When testing a hydraulic check valve, it is important to test different functions to ensure that it will work well with your systems. The two main functionality parameters tested include;
- Differential pressure testing. This is done by turning on the hydraulic system to create the maximum pressure that is found in the system. A pressure gauge is used to record the changing pressure in the system. A relief valve is to alter the pressure in the system until there is no pressure.
- Internal leaking test. It is done to determine the amount of leakage at varying pressure levels in the system. This test is done by turning on the system after releasing the relief valve for a base setting. The relief valve Is then adjusted to create different testing pressure levels. Amount of leakage experienced is collected and measured. It is done at different pressure levels until the leakage stops.
There are also additional tests such as cracking tests and air compression tests that are typically carried out by the manufacturers.
Check Valves for Hydraulic Applications
Hydraulic check valves are used in hydraulic systems to control the flow of fluid. Hydraulic systems can be used in several areas including pipelines, automotive and aerospace as well as simple household appliances. The uses of the check valves include
- Control the direction of fluid flow by preventing backflow like the ball valve
- It can be used to regulate the pressure of the fluid for example the in-line valves
- The check valves can be used to start and stop the flow of liquid as in the case of pilot-controlled check valve
- Check valves such as the modulator can be used to control the pressure and speed of the flow of fluid.
Hydraulic Calculations – Source: Target Hydraulics
Importance of Check Valve sin Hydraulic Systems – Source: Machinery and Lubrications