The Ultimate Buyer's Guide for Purchasing Nozzle Check Valves

Check valves are crucial devices in many systems. The main applications of check valves are in pump outlets, pipelines, and compressors to protect equipment by preventing the backflow of fluid. 

Goto Disai to know more.

They prevent backflow by using the pressure differential between the inlet and outlet areas. With backflow prevention, fast-acting check valves also prevent water hammering caused by pressure surges and vibrations.

Available in non-slam, ball, dual plate and other types, check valves have various types and varying parts, and some check valves operate with unique mechanisms. 

This post explains what a check valve is, discusses its functions, parts, types, and working principle and highlights other essential information.

What Is A Check Valve?

Dual Plate Check Valves

A check valve, also called a non-return valve, retention valve, or one-way valve is a device through which fluid flows in only one direction. A check valve has two openings or ports, one of which is called an inlet because fluid enters the valve through it, and the other is called an outlet because fluid leaves the valve through it. 

Check valves function to prevent the reversal of fluid flow (backflow) in the system to which they are applied. They are used in applications where the backflow of fluid may contaminate the fluid moving into the system.

The check valve works with changes in pressure in the system. The valve opens to allow flow through the inlet when the inlet pressure is higher than the outlet pressure and closes to restrict flow when the outlet pressure is higher than the inlet pressure. 

The valves may also close due to the check valve weight, a spring, or other means depending on the valve type. These valves are automatically activated and are hardly operated on-site or remotely as most of them do not have handles or stems. 

Check Valve Symbol

Source: PNG Wing

The check valve symbol is composed of a triangle with two horizontal lines extending from two opposite sides of the triangle. A vertical line is inserted at the meeting point of the pointed end and the horizontal line.

The horizontal lines indicate that the check valve has two ports-inlet and outlet. The pointed triangle and vertical line show that flow is allowed upstream, but backflow is restricted in the check valve.

Types of Check Valves

Check valves are differentiated into types based on the movement of the valve closure element or member and the process with which it shuts off to prevent backflow. The types of check valves include: 

1. Swing Check Valve

The swing check valve is the most commonly used. It operates with a disc which swings on a hinge or a shaft. As inlet pressure increases, the disc swings off the valve seat and fluid is allowed to flow through the valve, and as inlet pressure decreases or there is backflow, the disc swings back to the seat to restrict the fluid flow.

This check valve offers minimal restriction to flow when open. When springs are not used to assist the valve in closing, the valves should be mounted to allow the disc to shut with gravity.

2. Lift Check Valve

The lift check valve can be installed in many ways, including horizontally, vertically and angularly. It uses a disc which lifts to allow the flow of fluid upon an increase in inlet pressure. 

This check valve requires the inlet pressure to be higher than the cracking pressure to allow the fluid flow. The inlet pressure pushes the disc against gravity or a spring force. The valve closes when the inlet pressure decreases below the cracking pressure or there is backflow.

3. Dual Plate Check Valve

Dual plate check valves are commonly used in industrial operations and refineries. They are compactly built and can handle huge fluid backflow that other weaker types of check valves will not handle.

These check valves have double metal plates and are lightweight, making them easy for installation, transport and storage. They are mostly designed as non-slam types and usually result in low fluid pressure losses.

The purpose of these check valves is primarily to handle water hammer that results from accumulated pressure in the valve. Also called nozzle check valves, the disc in this valve has an internal spring which compresses when the valve is open.

When the inlet pressure decreases, the spring pushes the disc forward to the valve seat, closing softly to prevent water hammering. The mechanism of the non-slam check valves prevents pressure spikes and vibrations in the valve.

5. Wafer Check Valve

Source: India Mart

The wafer check valves consist of wafer-style discs that swing to allow or restrict fluid flow. The valve disc is attached to a hinge or spring, which controls the opening and closing.

These valves offer minimal obstruction to flow and, because of their slim and lightweight construction, are applied in many operations. They are very similar to the butterfly check valves and may be used instead of the butterfly check valves.

6. Diaphragm Check Valves

Source: Engineering Learn

The diaphragm check valves allow fluid flow by flexing its rubber diaphragm open when inlet pressure is increased. When inlet pressure decreases, or there is a backflow of fluid, the diaphragm closes to seal the passage.

The two diaphragm check valves are the free-floating normally open valve and the fixed-flexing normally closed valve. 

The free-floating diaphragm does not require a cracking pressure, while the fixed flexing diaphragm requires an amount of inlet pressure to contract and allow fluid flow.

7. Spring Loaded In-line Check Valve

Source: Engineering Learn

Spring-loaded inline valves can also be called nozzle or silent check valves. These valves require an inlet pressure high enough to overcome the cracking pressure and spring force for the valve&#;s orifice to open and allow fluid flow.

The valve closes by spring force when there is a decrease in the inlet pressure or back pressure pushing the disc to shut the valve. These valves also prevent pressure variations; hence they are good for handling water hammer.

Installation of the in-line check valves can occur vertically or horizontally. 

8. Spring Loaded Y-Check Valves

Source: Engineering Learn

The spring-loaded y-check valves have a &#;y&#; shape, as their name implies. They operate like the spring-loaded inline check valves, where high inlet pressure is required to overcome the cracking pressure and spring force.

However, unlike the in-line valves, the spring of the y-check valve and the valve disc is at an angle which enables them to be serviced while still connected to the system. These valves require more space than the in-line valves.

9. Stop Check Valve

Source: India Mart

The stop check valve function is a combination of two valve functions. These valves function as blocking and throttling valves and as check valves to restrict fluid reversal in the system.

The stop check valves have an actuator on the top of the valves used to control the opening and closing of the valves. These industrial check valves find applications in steam operations such as boiler circulation, steam generation, or power plants.

10. Ball Check Valve

Source: Alibaba

The ball check valves use a spherically shaped ball to seal the valve. The ball is moved by a spring or acted upon by gravity. When the inlet pressure increases, the ball is pushed by the pressure away from the curved seat to allow the flow of fluid through the valve.

As the inlet pressure decreases or there is backflow, the disc shuts off the valve due to spring force or gravity.

11. Foot Valve

Source: Made-in-China 

These check valves find application in operations where the suction line is under the pump. The foot check valve comprises a check valve and a strainer in the inlet area. 

The strainer restricts pipe fragments or substances from entering the valve and clogging downstream instruments.

12. Duckbill Valve

Source: India Mart

The duckbill valve, as the name implies, has an end resembling a duck beak. The flat end, with increased inlet pressure, opens to allow the fluid to flow through it, and when there is a decrease in inlet pressure, the valve closes and returns to its original state.

13. Tilting Disc Check Valves

Tilting disc check valves are a modification of the swing check valves. In this valve, the hinge at the top of the disc in the swing check valve is replaced by a pivot point with a double offset from the center of the disc. This valve can open at lower pressures than the swing check valve.

Check Valve Parts

The purpose of check valves is to prevent flow reversal in the system. To restrict backflow, every part of the check valve plays a role. Check valves have different types and forms, but they all use the same principle. 

Check valves have varying parts as the components that make up a particular check valve may not be the same in another. However, these are three parts that can be found in most check valves: 

1. Inlet port 

This part of the check valve allows the fluid to enter. This part is usually shut or open with the valve closure element.

2. Valve body 

This is the vessel through which the fluid passes.

3. Outlet Port

The fluid leaves the check valve through this part. It usually serves as the first port for a backflow.

Different types of check valves have unique parts. Some parts may look the same but do not have the same function in different types of check valves. Below are some check valves and their parts.

Ball Check Valve

• Inlet port
• Gasket
• Body 
• Cap 
• Clamp 
• Ball
• Outlet port

Diaphragm Check Valve

• Inlet port
• Diaphragm 
• Outlet port

Stop Check Valve

• Inlet port
• Actuator
• Stem 
• Bonnet 
• Body 
• Disc 
• Seat
• Outlet port

Duckbill Check Valve

• Inlet port
• Elastomer or rubber flaps
• Outlet port 

Lift Check Valve

• Inlet port
• Seat
• Plug
• Body
• Bonnet 
• Outlet port

Other check valves include unique parts such as stoppers, spacers, springs, cages, etc.

What Does A Check Valve Do?

Check valves are designed to allow fluid flow in one direction only. They operate automatically using the pressure in the fluid to either open and allow fluid to move through or close to prevent fluid from moving out. 

The main functions of the check valves are: 

• They prevent the backflow of fluid in the pipeline system.
• They stop the pump and its generator from reversing.
• They prevent the backflow of fluid from the container.

Backflow of fluid can cause contamination, water hammer and other system damage. Some check valves, such as the stop check valve and the foot valve, have other functions asides from preventing backflow. 

Explore more:
How Does a Double Block and Bleed Valve Work
Rig Site Tips: Running Casing Procedures and Instructions
What Factors Influence Forged Trunnion Ball Valve Price?

Want more information on Nozzle Check Valves? Feel free to contact us.

For example, the stop check valve may also be used as a throttle or isolation check valve, and the foot valve also functions to block debris from moving further into the pipeline.

The check valve may also be used as an auxiliary system in cases where the pressure can increase above the pressure of the main system. Check valves such as the non-slam check valve primarily prevent water hammer in the system.

If a backflow of fluid occurs and the system does not have a check valve installed, a water hammer may occur and destroy the pipeline parts.

How Does A Check Valve Work? 

The check valve working principle involves two major areas: Opening and shutting the valve.

Opening The Valve 

For the valve to be open, it requires a minimum upstream pressure provided by the fluid. The minimum pressure is the differential between the pressures at the inlet and outlet areas. It is called the check valve &#;cracking pressure&#;.

When the cracking pressure is overcome, the valve opens and allows fluid flow. Cracking pressures are specific to different valve types. Hence, proper research should be done to ensure the system can generate the cracking pressure of the check valve.

Shutting The Valve

If the pressure at the inlet (upstream pressure) decreases, falling below the cracking pressure, or there is a backflow of fluid, the valve shuts. The closing operation and closing element depend on the valve type and design.

For proper operation of the check valve, the valves should be installed correctly. The valves should be examined for correct installation because installing wrongly could damage the system. 

Check Valves Selection Criteria 

Various factors need to be considered before the selection of a check valve for a system. Some of these factors are: 

Valve Material

The fluid makes contact with the valve while passing through it. Hence, the material of the valve must be compatible with the fluid to prevent contamination. 

Fluid 

The check valve must be able to handle the fluids for the intended operation. Most check valves can handle normal fluids without suspended solids, but specific check valves can handle fluids with suspended solids, such as raw wastewater or sewage water.

Pressure

The fluid must be able to generate enough pressure to overcome the cracking pressure of the selected valve. Also, in some cases, it should be confirmed that the fluid can generate enough back pressure to seal the valve.

Pipe Size and Connection

The fitting of the valve with pipe should be considered. The size of the check valve and its parts should correspond with the required size of the pipe. 

Operating Conditions

The fluid and external temperature conditions should be compatible with the valve type. Also, the installation of the check valve type should give enough space for repairs and inspections.

Check Valve Installation and Maintenance 

Installation Of Check Valves

For check valves to work effectively and with optimal efficiency, they have to be installed properly. Mistakes in the installation of the valves may result in damage to the valve and the pipe system. Here are some installation best practices that apply to most check valves:

• The selected check valve should be appropriate for the pipe size and connection, the fluid material, and operating conditions, as selecting the wrong valve may lead to premature wear.
• The check valves should be positioned properly. Check valves differ in their ability to function in horizontal or vertical piping runs. Also, enough space should be given from the valve position to other devices that can cause turbulence.
• The flow arrow on the valve should be checked and followed to ensure the proper valve orientation.
• The valve should be test run after installation to ensure that all parts are stable for operation.

Maintenance of Check Valves

Most check valves from industrial valve manufacturers are of different materials and parts. Therefore, for proper check valve maintenance, following the maintenance guide from the manufacturer is always best. 

However, below are some effective maintenance guidelines for most check valves.

• Check valves should be inspected twice a year or as often as the manufacturer recommends. On-site inspection should be done, and the check valve parts should be cleaned.
• Debris and sludges should be removed, and they may affect seal integrity. If some parts need to be washed, dislodge the valve to wash and reinstall.
• Replace any broken or worn-out parts of the check valve.
• Clean the closure element properly&#;test after reinstalling. Water can be used for proper testing.

What To Consider To Buy A Check Valve

The material, standard, sizes and designs of the check valve should be compatible with the application. Below, some of these specifications are discussed.

Check Valve Materials 

These are the types of check valve materials to consider.

PVC (Polyvinyl Chloride)

Check valves made from PVC material are insusceptible to corrosion. They can be used with corrosive fluids such as acids and other caustic chemicals. However, they may be damaged by aromatic and chlorinated hydrocarbons. 

Polypropylene 

Check valves made from polypropylene are also insusceptible to corrosive fluids such as inorganic acids and bases. They have a maximum temperature of around 80 degrees and find applications in water systems and food products.

Brass

These check valves find applications in systems that use air, water, oil and fuel. They are more susceptible to corrosive fluids than the other material types. They are mostly used in low-pressure applications and small systems.

Stainless Steel 

These valves are resistant to corrosive fluids and low-temperature conditions. They also offer good structure and have solid construction. However, they are a less economical option than the PVC and brass material types.

Check Valve Design

The check valve has several types and designs, and some types are more suitable for certain applications than other types. Some check valve designs are listed below:

• Swing Check Valves: These valves are very common and readily available. They have low cost and result in low-pressure losses when open.
• Lift check valves: These are simple, automatic and cost-effective but may have high energy costs in the long run.
• Spring In-line Check Valves: These valves have low cracking pressure because of the large area of the closure element.

Other check valve designs have characteristics that make them suitable for specific operations.

Check Valve Standards

The check valve standards should be complied with when buying a check valve. These are some standards followed during piping design: 

API Standards

• API Spec 6D, API Std 594

ASME Standards

• B16.34

AWWA Standards 

• C508, C510

BSI Standards

• , , , , , , ,

MSS Standards

• SP-42, SP-61, SP-71, SP-80, SP-84

Check Valve Size

Check valves depend on fluid pressure at the inlet to open or close. Hence, knowing how much the valves open to allow fluid flow through the pipe is essential to effectively operating the valves. Check valve sizes inform on the spatial capabilities of the valve and if it is compatible with the pipes. 

The most important consideration in selecting a check valve size is its application. The operation the check valve is intended for determines the size used. Calculating the valve size requires the material viscosity, pressure, temperature, and flow rate; with these flow characteristics, a valve size can be customized for the application.

An operation in which a wrong check valve size is used may lead to higher pressure losses, unstable flow and a shorter valve lifespan.

Check Valve Working Pressure

The pressure ratings of the check valve vary depending on the manufacturer. Some common ratings are: 

• Water, Oil, and Gas (WOG): This is a pressure rating for valves at room temperature.
• Cold Working Pressure (CWP): This pressure rating for valves between -20 and -100F.
• Pressure Nominal (PN): This is a PSI rating that some manufacturers include.

Conclusion 

This post discussed all you need to know about the check valve, including its function, parts, installation and maintenance requirements, and what you need to consider before buying an industrial check valve.

Dombor valve is an industrial valve manufacturer that provides high-quality valve solutions to fit market requirements and pipe specifications. We pride ourselves on creating suitable valve types in various conditions. So contact us today!

Tilting disc, slanted seat check valves

The slanted seat check valve also offers enhanced resistance to water hammer. The valve has a double eccentric shaft position as well as an increased seating angle. This yields a shorter valve stroke, thus reducing the time taken for the door to close.

Hydraulic dampers are recommended, especially when the valves are installed on a pumping station where high frequency opening and closing of the valve is required. The valve disc closes quickly over the first 85% of its angular travel before meeting the hydraulic damper. The damper then dissipates the kinetic energy of the disc and forces it to open slightly. The disc closes until it contacts the damper again and this cushions the disc until it returns to its fully closed position, sealing the valve. This function greatly reduces the onset of water hammer due to the damped and controlled method of valve closure. 

Hydraulic dampers are recommended, especially when the valves are installed on a pumping station where high frequency opening and closing of the valve is required. The valve disc closes quickly over the first 85% of its angular travel before meeting the hydraulic damper. The damper then dissipates the kinetic energy of the disc and forces it to open slightly. The disc closes until it contacts the damper again and this cushions the disc until it returns to its fully closed position, sealing the valve. This function greatly reduces the onset of water hammer due to the damped and controlled method of valve closure.

For more details, please see our slanted seat check valve product information.

Nozzle check valves

Nozzle check valves are designed with the valve disc connected to the stem which is guided on the central horizontal axis. A spring is positioned between the disc and the diffuser sleeve. When flow enters the valve, the hydraulic force exerted onto the front face reacts against the spring, causing the spring to compress and allow the valve to open. When the flow stops, the spring forces the disc to return to the closed position.

Due to the spring-assisted closure and the short linear valve stroke, the nozzle check valve is one of the quickest acting check valves available and is commonly used in pumped systems where water hammer is a potential concern. Because the disc is constantly in the direct line of flow, the head loss characteristics of this valve are higher compared to that of conventional swing check valves.

For more details, please see our nozzle check valve product information.

What to consider when choosing your check valves?

In order to choose the right check valve for your application, several selection criteria should be considered. First, however, there is not one type of check valves being the best choice for all applications, and the selection criteria may not be equally important for all cases. Some of the things you may need to consider are fluid compatibility, flow characteristics, head loss, non-slam characteristics and total cost of ownership.

Fluid

All check valves referred to in this article are designed for water and treated wastewater applications, but using the valves for raw wastewater/sewage applications may cause some issues. When selecting a valve for these fluids, you should consider how the presence of solids may potentially affect operation of the valve.

Flow characteristics

If a check valve closes very fast, it may prevent slamming against upstream equipment such as pumps. However, the rapid closure will not protect against the surges caused by pumps being started and shut down. If the valve opens (and closes) quickly, the flow will change rapidly and thus increase likeliness of surge occurrence.

Head loss

Head loss is, among other things, a function of fluid velocity. The head loss through a valve is determined by the internal design of the valve and the opening degree. When a valve is designed with a restricted (narrowed) opening compared to the pipeline, the velocity will increase through the valve, increasing the head loss as a result. Vice versa, if a valve is designed with less restriction and bore is equal size to the pipeline, the head loss will be smaller, and the valve will in practice not affect the overall head loss of the system. There are a number of values for head loss, amongst others zeta values, Kv and Kvs values.

Total cost of ownership

The costs for your check valve consist of more than just the purchase price. For some installations, the most important costs may be purchasing and installation, but in other cases, maintenance or energy costs may be equally or even more important. Also protecting more valuable equipment such as e.g. pumps has to be considered, and looking at the valve performance will be crucial. When considering costs as a selection criterion for your check valve, the total costs over the life of the valve should be considered. In general, the simpler the valve construction is, the lower are the maintenance requirements. The higher the Kv value, the lower the energy consumption. The higher the performance, the better the protection ability.

Non-slam characteristics

Check valve slam can affect pressure surges in a negative way. First step of the process is when the pump stops, starting the pressure surge. Second step is, when the flow is reversed, slamming against the fully closed check valve. If the check valve closes too fast, the kinetic energy is turned into high pressure, stressing the pipes, and causing high noise.

A slam sounds like if the disc or the ball from the check valve is hitting the seat and can make quite some noise. However, the sound is not caused by the physical closing but by a sound wave arising from a pressure spike stretching the pipe wall.

To prevent the occurrence of check valve slam, the valve should close in a controlled way and slower when near closed position. For a check valve to close slowly, it requires additional ancillary equipment, such as hydraulic dampers, which act as a cushion to the valve door, as it comes into its seated position. This slower closure allows the fluid to pass through the check valve until it closes, causing less kinetic energy turning into high pressure, and thus less energy to feed and maintain the surge. Consideration must be given to the upstream pump to ensure that it is suitable for reverse spin and flow.

As swing check valves have the disc in the flow stream, helping with rapid closure, they have better non-slam characteristics. However, today many pumps are frequency converted, enabling them to adjust the start-up and closure time to avoid water hammer.