By Gilbert Welsford Jr., ValveMan
Check valves are indispensable safety components, used in industrial and residential piping systems to provide directional control of fluids. These valves are specifically designed to facilitate fluid flow in one direction, and restrict fluid flow in the opposite direction. Preventing fluid backflow protects critical piping equipment, such as pumps, from damage by pressure surges or hydraulic hammers.
Check valves are pressure sensitive devices that operate based on pressure differences, offering minimal resistance to upstream fluid flow, and closing when the pressure drops below cracking point (minimum upstream pressure). Check valves can close by means of the weight of their closing element responding to gravity, by the action of a return spring, or by a combination of both.
While directional fluid control is a straightforward process, selecting the appropriate type and size of the check valve is vital for satisfying the operational need of dispensing fluids safely. Below are some of the major types of check valves and their broad industrial applications categorized based on the mechanical movement of flow control members.
SWING CHECK VALVE
A swing check valve utilizes a flap or disc that is of the same diameter as the pipe’s bore. The flap is designed to offer minute resistance to the working medium, eliminating turbulent fluid flow. The flap is aptly hinged, so as to freely swing from the valve seat.
A tilting disc check valve is a modification of the conventional swing valve that has the flapper pivoted closer to its center, allowing the fluid to flow above and below the disc. Though the tilting disc check valves have higher resistance to fluid flow, they tend to open up at lower cracking pressures. Swing check valves have excellent sealing characteristics, with a compact structural design to ensure a shorter flapper stroke, limiting the valve’s shutting impact.
Swing valves are predominantly used in domestic and industrial water supply pipelines, wastewater pumping systems and conveyance of industrial slurry. It is inadvisable to use swing check valves in pulsating or low-pressure flow media.
FOOT VALVES
The valves are designed for installation at the bottom, or at the inlet ports of multiple piping systems, and act as mechanisms that prevent gravitational backflows. The valve has a screen – or a filtration shield – that blocks debris and foreign matter from entering the upstream line. Foot valves feature wider inlet openings as compared to upstream pipes, in order to minimize pressure losses.
The strainer on the inlet side protects the valve and the piping system from frictional deterioration. Depending on the industrial application and nature of the working medium, it is vital for the strainer to possess adequate mesh sizes, which provide efficient filtration and are capable of preventing choking during suction.
Foot valves are commonly used with hydraulic and pneumatic pumps, intake pumps and sump pumps, wells, ponds, and pools.
DOUBLE DISC CHECK VALVE
Dual disc check valves are fast acting, self-actuating check valves designed with two centrally pivoted, semi-circular discs. The valves are suitable for a wide range of fluids, application in chemical piping systems, fire protection utilities, and low-pressure portable water systems.
The dual discs are designed to work independently and feature a spring assisted pivot that keeps the valve on its seat. The semi-circular discs are lightweight and ideal for installation in tightly spaced piping systems. Dual disc check valves provide great hydrodynamic efficiency, limiting overall pressure losses.
These valves have been designed to withstand extreme fluid pressure through the uniform distribution of stresses. Double disc valves have impressive non-slam and sealing characteristics. They are highly efficient valves whose operation is marked by low-pressure drops and by extension have nominal energy losses.
BALL CHECK VALVES
These valves rely on a spherically shaped ball that moves up and down a conically shaped valve seat. The lateral motion of the ball from its seat occurs due to variations in fluid pressure. Ball check valves are essential for high-pressure piping systems that demand strict contamination controls.
The freely rotating ball is subjected to even wear and tear, making the valves suitable for the conveyance of viscous fluids. Ball check valves have been designed as self-cleaning and prevent the accumulation of trash. Though ball valves are cheaper and simpler in design, they require additional cushioning to protect them from slamming.
Ball valves are low maintenance valves that can be installed in vertical and horizontal orientations, with prime applications in the chemical industry for the conveyance of corrosive fluids and slurries, chemical storage facilities, metering pumps, and clean water supply systems.
SILENT AND RESTRICTOR CHECK VALVES
High-pressure shock waves place extreme stress on the pipes, increasing the susceptibility of the pipes to ruptures. The valves are primarily spring loaded, keeping the valves tightly seated. The silent and restrictor valves, usually referred to as non-slam valves are used to prevent hydraulic hammer for upstream axial flow. The valves open and close promptly, combating intermittent fluid shockwaves.
These valves are used in a variety of industries, including commercial gas transmission systems, water treatment plants, power generation utilities, textile manufacturing industries, and chemical processing plants.
Y-TYPE CHECK VALVES
These valves are designed to provide easy maintenance without significantly affecting directional fluid flow. Y-type valves have spring loaded discs that move up and down the valve seat at an angle.
The valves offer the tiniest flow resistance when fully open and limit pressure drop in piping systems. Y-type valves are highly preferable for seasonal pipeline operations such as throttling during start-up.
The valves are predominantly used in high-pressure piping systems in chemical industries, power generation facilities, and wastewater piping systems, in which dirt periodically accumulates around valves.
DIAPHRAGM CHECK VALVES
Diaphragm valves utilize a flexible rubber membrane that opens up when inlet pressure increases and overcomes the elasticity of the rubber. Unlike some other valve types, diaphragm valves respond at minimal cracking pressures for their opening. As upstream fluid pressure rises, the diaphragm flexes increasingly, allowing more fluid to flow.
As back pressure builds up, the diaphragm is forced against its seat, blocking the reverse flow. The valves are commonly used in low-pressure industrial piping systems and vacuum pipelines.
ABOUT THE AUTHOR
Gilbert Welsford Jr. is the founder of ValveMan.com and a third-generation valve entrepreneur. He has learned valves since a young age and has brought his entrepreneurial ingenuity to the family business in 2011 by creating the online valve store. Welsford’s focus is building on the legacy his grandfather started, his father grew, and he has amplified.
MODERN PUMPING TODAY, June 2021
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