Ball check valve for pressure protection

In hydraulics and pneumatics, a ball check valve is a simple component used to regulate a volume flow. Its technically simple design makes it a very cost-effective and popular component. Another name for the ball check valve is the “ball check fitting.” It is related to ball valves, but not to “ball cocks.” The frequent designation of the latter as a “ball valve” is technically incorrect and should be avoided.

Function of ball check valves

As the name suggests, the primary function of the ball check valve is to prevent the backflow of a volume flow. It is therefore primarily a standard check valve, such as those found in the simplest hydraulic designs, for example, jacks or pallet trucks. In contrast to the flap check valves commonly used there, the ball check valve works with a steel ball. A fundamental distinction is made between two designs:

• Gravity ball check valves
• Spring-loaded ball check valves

Gravity ball check valves

Gravity ball check valves consist of a vertically arranged hydraulic line with a constriction. The ball is located above the constriction. The volume flow coming from below pushes the ball to the side and can continue to flow upwards. When the volume flow is interrupted, the ball rolls back into the constriction and thus seals it hermetically. The hydraulic fluid can then no longer flow downwards.

Spring-loaded ball check valves

In spring-loaded ball check valves, the ball is clamped in a coil spring. The volume flow must first overcome the spring force of the coil spring before it can flow past the ball. This requires a certain hydraulic pre-pressure. If the hydraulic pressure drops below the required pre-pressure, the spring closes the passage again with the ball.

Advantages and disadvantages of spring-loaded or gravity ball check valves

Gravity ball check valves have several disadvantages compared to spring-loaded ball check valves: they must always remain in a vertical position. This makes them primarily applicable to stationary hydraulic systems. In mobile systems, the function of gravity ball check valves would be significantly impaired even by slight inclinations of the machine. Furthermore, only a very small force is required to overcome the gravity of the closing ball. This makes gravity check valves rather unsuitable for complex hydraulic circuits with regulatory functions.

Spring-loaded check valves can be used in any direction. This makes them the preferred design for mobile hydraulic systems. Due to the pre-tensioning of the spring, the hydraulic system can be designed to be more complex. For example, by connecting spring-loaded check valves with different pre-tensions in parallel, it is possible to activate different subsystems as the hydraulic pressure increases.

Defects in ball check valves

Ball check valves are located at critical points. With high pre-tensioning of the compression spring, a correspondingly high pressure is required to overcome it. As soon as the spring force is overcome and the ball is lifted, the hydraulic oil shoots past the ball at high pressure. This can lead to abrasion damage or cavitation. It is therefore always recommended to check ball check valves regularly for damage or to replace them at regular intervals.