29 November 2023

Hydraulic check valves: everything you need to know

Hydraulic check valves

A hydraulic check valve, also known as non-return valve (NRV), is a mechanical device designed to allow fluid (typically a liquid) to flow in one direction and prevent reverse flow; it plays a crucial role in hydraulic systems to maintain the direction of fluid movement or to control pressure or flow rate.

Generally check valves are automatically operated; human intervention or any external control system is not required.

How Hydraulic Check Valves Work

Check valves have a body (often cylindrical) with inlet and outlet ports for fluid to enter and exit; inside there’s a movable element (often a poppet, more rarely a ball) whose function is to block the flow in the reverse direction. When fluid flows in the desired direction, its pressure forces the poppet away from the seat, allowing the fluid to pass around the valve. Vice versa, if there’s an attempt at reverse flow, pressure from the fluid pushes the poppet against its seat. This seals off the passage and prevents fluid from flowing backward. In most cases, a spring helps to close the poppet quickly and effectively when the flow direction changes, preventing backflow.

Check valves must necessarily be installed in the correct orientation; in fact, they are designed to allow flow in one specific direction, so improper installation will result in valves not functioning as expected. When fluid flows in the desired direction, the valve opens, and when there’s an attempt at reverse flow, the valve closes to prevent backflow. This design is crucial for maintaining the efficiency and safety of hydraulic systems by preventing unintended fluid movement in the wrong direction.

Types of Hydraulic Check Valves

Check valves usually have a straight profile and one single body or two screwed semi-bodies. Inlet and outlet threads can be female or male type.

A special category is represented by parts where an orifice machined on the poppet allows controlled leakage of fluid in the direction in which the flow is normally prevented by the closure of the valve. This design trick makes check valves equipped with an orifice a flow control tool. There are also three-way valves (or “shuttle” valves), which have the characteristic of conveying to the return line of the circuit the greater of the pressures of the two delivery lines.

Differences Between NRV and Check Valves

Understanding the nuances between NRV (non-return valves) and conventional check valves is crucial in hydraulic systems. While often used interchangeably, these terms essentially refer to the same component. The distinctions lie in regional preferences and industry jargon. In essence, whether you call it an NRV or a check valve, the functionality remains consistent, ensuring unidirectional fluid flow and preventing backflow. Clearing up any confusion between the terms is vital for precise communication within the hydraulic engineering realm.

Materials for Hydraulic Check Valves

In hydraulic systems, the choice of materials for hydraulic check valves is paramount, with carbon and stainless steel emerging as the most commonly utilized raw materials. These robust materials not only provide durability but also ensure the reliability and longevity of the check valves. The selection of carbon or stainless steel depends on the specific requirements of the hydraulic circuit. These materials play a pivotal role in maintaining the structural integrity of the check valves, contributing to their effectiveness in controlling fluid flow and preventing backflow. A careful consideration of these material options is essential in ensuring the optimal performance and longevity of hydraulic check valves in diverse applications.

Hydraulic Check Valve Symbol

In the realm of hydraulic systems, the symbolic language of hydraulic check valves is conveyed through a stamped valve symbol on the external body. This symbol serves as a visual identifier, facilitating easy recognition of the check valve among other hydraulic components. This simplistic yet informative feature aids in the swift and accurate identification of check valves in complex hydraulic circuits. It is a valuable element for engineers and maintenance personnel, streamlining troubleshooting and ensuring efficient operation. The presence of a clear and standardized valve symbol enhances the overall functionality and usability of hydraulic systems, promoting ease of maintenance and optimal performance.

Common Hydraulic Check Valve Problems

As with all complex components in a hydraulic circuit, it’s possible to experience issues with check valves too, the most common being the stuck of poppet in open or closed position, unexpected leaks, chattering or the valve not opening at the set pressure. Choosing products suiting the circuit specifications, installing them properly and performing some periodical maintenance can help prevent many of these issues from occurring in the first place.

Why Choose Faster Hydraulic Check Valve

With a long experience of design and production, Faster is the ideal supplier for top-quality check valves. Every day we deliver all types of valves (ball-type, poppet-type, shuttle-type, etc.) to our customers to allow control of directional flow, or pressure, or flow rate for a wide range of applications and for different markets.