Types of Check Valves: Which One is Right for You?

 A check valve is a device that only allows flow in only one direction. Therefore, we can also refer to them as unidirectional, non-return, or automatic valves. Check Valves open with the forward flow and close with reverse flow. All types of check valves are relatively simple in design but choosing the right and the proper one is critical for continual operation. Using the wrong type of check valve can create operability issues and continuous requirement of valve maintenance. This article intends to guide our customers to select the best check valve for the application at hand. We have defined the best criteria for your ease to choose correctly, keeping in mind key types, materials, and technical requirements for a specific application.   

Here are Types of Check Valves 

 There are numerous types of check valves available in the market with different sizes and pressure rating requirements. Some of the types of check with applications from industry to daily life are:

· Swing Check Valve

· Tilted Disc Check Valve 

1. Wafer titled disc check valve

2. Lug titled disc check valve

· Lift Check Valve

1. Globe/Plug Lift Check Valve

2. Ball Check Valve

· Dual Plate Check Valve 

All of the types above have a specific design, materials, working mechanism, and applications. 

Swing Check Valve                                

Working Mechanism 

 Swing check valves are the most basic check valves available in the market. Swing check valves work on rely on pressure differential to operate. The disc in the swing type check valve is unguided as it fully opens and closes. The valve is open when there is flow in the line and closes when there is no flow. The minimum upstream pressure required to cause flow is called check valve cracking pressure. 

Design

Disc and seat designs can be metal-to-metal or metal to composite. Swing check valves have very low turbulence and pressure drop. The seating angle, the angle between the seat and vertical plane, usually varies from zero to 45 degrees. However, for swing check valves seating angle ranges from five to 7 degrees. The larger the seating angle reduces the disc travel. So, by increasing the seating angle valve, and can be open and shut quickly. This will also minimize water hammer possibility. A vertical seat has a zero degree angle. In process applications, the combination of check valves and gate valves are handy for providing free and unobstructed flow. 

Basic Components

Check valves do not have a handle, gearbox, or stem as in butterfly valves. Also, check valves contain the following components.

· Valve Body

· Bonnet Cover

· Hinge

· seat 

· disc

· Assembling Accessories (Nuts & Bolts) 

Applications 

Where Tight Sealing is required 

Swing check valves have a tight shutoff than any other check valve, which comes from flat seats. Swing check valves also have a flexible connection between the disc and seat to accommodate any minor misalignment, thus maintaining tighter shutoff. An elastomeric dual-core can provide the best results to have a stricter shutoff irrespective of the differential pressure range. 

Where Flow is Relatively Constant

As we know, swing check valves work on the principle of pressure differential. Therefore, they are not the best choice in applications where pressure is relatively low or pulsating flow rates or rapid flow reversal. Swing check valves are also less rugged as compared to other check valves due to extra moving parts. Also, there can be high impact loads on disc during quick opening and shutoff. 

Where Water Hammer Occurrence does not Pose Problem

Water hammer can be extremely annoying in process operations and particularly swing check valves. Check Valves do not have any protection against water hammer. In swing check valve disc have to travel a considerable distance from fully open to close position. The time required to reach a fully secure place can cause significant reverse flow. When disc seats are under this condition, water hammer can occur. 

Where Pressure Drop must be kept to a Minimum

Swing check valves have a straight-through design and clear waterway. This keeps pressure drop to a minimum. Therefore, swing check valves working on pressure differential can be the best choice. 

Installation in Horizontal and Vertical Direction

We can install swing check valves in horizontal as well as vertical directions. For vertical direction installation, the flow direction is usually upwards to provide gravity assistance in keeping effective disc closure. 

Ease of Maintenance  

Due to easy construction, simple design, and flat seats, swing check valves are the most straightforward check valves to maintain. 

Tilted Disc Check Valves

Titled disc check valves are an upgraded form of swing check valves. They overcome shortcomings available in swing check valves. 

Working Mechanism and Design

Titled disc check valve design enables to remain fully open, remain steady at lower flow rates, and close quickly when the flow stops. The disc is a dome-shaped, fluid flow on both the bottom and top sides of the disc surface. Its disc is spring loaded. Therefore, when forward flow pressure reduces, the spring force closes the valve quickly. Tilted disc check valves are also available in wafer and Lug type design. 

Basic Components

Check valves do not have a handle, gearbox, or stem as in butterfly valves. Also, check valves contain the following components.

· Valve Body

· spring

· disc

· Hinge

· Supports

· Disc Seat

· Assembling Accessories (Nuts & Studs)

Applications 

Where Fast Opening and Closing is required

The center of gravity for the tilted disc check valve is very near to the axis of rotation. Thus it can open and close very quickly without damaging seat or disc. Since it opens and closes very soon upon reversal of fluid and significant flow velocity does not develop in the reverse direction, minimizing the effect of water hammer. 

Stable at Low and Pulsating Flows

Due to tilted disc check valves’ design, it is beneficial at low and pulsating fluid flows compared to swing check valves. 

Moderate Pressure Drop

The pressure drop across the tilted disc check valve is significantly less from the lift check valve but slightly higher from straight flow swing check valves. A titled disc design will flow from the top and bottom and cause minimal pressure drop from the center. 

Where Sealing is required

Tilted disc check valves provide moderate Sealing as compared to swing check valves. Sealing is significant where a higher-pressure differential exists. For tighter shutoff at low differential pressure, dual elastomeric seats are available. 

Installation in Horizontal and Vertical Direction Designs

In tilted disc, check valves both horizontal and vertical direction installation designs are available. For vertical lines, the flow should be kept upwards for gravity support in disc closure. The center of gravity location relative to its pivotal point is key to a well-designed tilted disc check valve. 

Lift Check Valve 

Working Mechanism and Design 

Seat designing of lift check valves is similar to the globe valve. The disc can be a plug, piston, globe, or Ball. We can divide it into two subtypes globe or ball lift check valves and plug lift check valves. When flow enters below the seat, a disk is raised from seat by the upward flow pressure. When the flow stops, the backflow or gravity forces the disc downward or on the seat. Ball-type design is straightforward as it solely works on the principle of sincerity. When the forward flow starts, it forces the Ball upwards, and when it stops ball rest in seat due to gravity. 

Basic Components

Lift check valves do not have disc as swing and tilting disc check valves. Even though it contains plug, piston, globe, or Ball as a disc. Lift Check Valves also include:

· Ball

· spring

· plug

· Valve Body

· seat

· Bonnet

· Assembly Accessories (Nut, Bolt & Studs) 

Applications 

Where Rapid Flow Reversal May Occur

Wherever rapid flow reversal may occur globe, lift check valves are an excellent selection. The time required from fully open to close position is the shortest. This helps to avoid water hammer. Inherently, lift check valves are rugged by design, have no hinges, bushings, or bolted connections. 

Excellent for Low or Pulsating Flows

As we know, lift check valves have the shortest stroke and fewer components under impact loads and wear. This makes it an excellent choice for low and pulsating fluid flow rates. For exceptional cases, lightweight discs are also available. Lightweight disc eliminates pressure drop at low fluid flow rates and low liquid flow rates, removes the possibility of chugging or simmering. 

Pressure Drop 

Pressure drop in lift check valves is generally higher than swing or tilted disc check valves. We can minimize this pressure drop by using a Y-lift check or angle check with an elbow in the piping system.

Installation Orientation

For optimum performance, we should install lift check valves with the neck upright and vertical. This position wear as the disc’s weight acts along the inlet’s centerline and seat. 

Dual Plate Check Valve

The double-disc check valve, also known as a butterfly check valve, folding disc check valve, double disc, or split disc check valve. Two plates or discs move towards the centerline with the forward flow and reverse flow. Two halves open and rest on the seat to close the flow as a flapping action. 

It is popular in low-pressure liquid and gaseous applications. Its lightweight and compact construction make it a preferable selection when space and convenience are essential. It is 80 to 90% lighter than other conventional full body check valves. We can also use it as a butterfly valve replacement. The cost of installation and maintenance is meager as well. 

Selection Parameters

The following table summarizes selection parameters and comparison of Swing, Titled disc, and Lift check valves.