Directional valves are widely used in fluid control applications. The simplest directional valve, both functionally and conceptually, is the check valve. Valves of this type are designed to allow flow in one direction while blocking it in the other direction. Some types of check valves, such as the pilot-operated check valves, are more complex, but the most commonly used valve in fluid power systems is the inline check valve. This blog will discuss what inline check valves are and when they should be used.
An inline component refers to any object located in a circuit and coupled to adjacent fluid conduits. Its name comes from its location in the line of the fluid connection. They are convenient and versatile, often added to enhance an existing circuit or as an upgrade to an existing machine. This is no different in an inline check valve, which has many uses. A majority of functions of a fluid power circuit require a one-way flow path, for which incline check valves often provide the best solution. For use in hydraulic systems, the check valve consists of a steel body with a spring-loaded ball or poppet held in place with a retainer. Pneumatic applications offer more versatility in construction because of the low pressure rating. This allows the materials to be made from brass, aluminum, and certain types of plastics or composites.
The most common use for inline check valves is to prevent the backward transmission of pressure, rather than flow, which is created by pressure. A good example of this is the check valve installed following the pump within a system that uses an accumulator. The check valve stops stored energy from traveling back into the pump which is especially important where there is energy in the accumulator and the pump is not running. This stored energy can be dangerous or damaging and must be regulated for a hydraulic system to be safe and reliable.
A similar type of check valve is the load sense check valve. In complex load-sensing applications, the pump or compensator only needs to sense the highest pressure of all functioning actuators to read the load sense signal from downstream. The load sense check valve network opens a parallel path of hydraulic fluid from each actuator to the primary compensator, and the channel with the highest pressure overcomes its check valve and in turn closes every other check valve in the network. Though these valves are not totally true to the inline name, they are still used in valve banks to open and close an inline flow path.
Inline check valves can also be added to existing hydraulic circuits to add function. For instance, say an inline needle valve was added to a compression-loaded cylinder application but the cycle time could be improved. A needle valve reduces flow in both directions, so the addition of an inline check valve located around either side of the needle valve bolsters flow control. This means Fluid will now bypass the needle valve and travel unimpeded through the check valve, providing full flow when extending.
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