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Check Valve Technical Guide

A check valve is a one-way valve. The main purpose of the check valve is to prevent system backflow, protect equipment, and reduce maintenance. Check valves are a cheap, effective, and simple solution to potential plumbing problems. If the fluid backflows in the pipeline, it may contaminate the upstream medium or damage the equipment. If a check valve is installed in the pipeline, it isolates the possibility of contamination between the upstream and downstream media and protects the equipment from reverse damage caused by backflow.

Check valves come in many sizes and materials to ensure there is a check valve for every application. All check valves have arrows on them that indicate the direction of fluid flow in the check valve.

Table of contents

Check valve working principle

Check valves work by allowing fluid to flow in one direction and automatically blocking flow in the opposite direction.

The check valve is a one-way automatic valve that does not require manual intervention when working.
The structure of the check valve is usually very simple, including valve body, valve seat, sealing disc and valve cover. These valves are flow sensitive and rely on pressure differences in the pipe to open and close the valve. As fluid passes through the valve, it forces the valve open. When reverse flow occurs, the valve is forced to close.
The main purpose of the check valve is to prevent system backflow, protect equipment, and reduce maintenance. Check valves are a cheap, effective, and simple solution to potential plumbing problems. If the fluid backflows in the pipeline, it may contaminate the upstream medium or damage the equipment. If a check valve is installed in the pipeline, it isolates the possibility of contamination between the upstream and downstream media and protects the equipment from reverse damage caused by backflow.

Check valves come in many sizes and materials to ensure there is a check valve for every application. All check valves have arrows on them that indicate the direction of fluid flow in the check valve.

How Check Valve Works?

Opening pressure

The check valve is an automatic valve that opens automatically when the upstream pressure in the pipeline is greater than the downstream pressure. The minimum upstream pressure at which the valve opens is called the “cracking pressure” of the check valve. The opening pressure of the check valve varies according to the design and size of the valve. When selecting a check valve, make sure that the pipeline system pressure can produce sufficient opening pressure.

Closing

If the downstream pressure is greater than the upstream pressure and flow attempts to be diverted from the outlet to the inlet, the check valve will close with the assistance of gravity or a spring. Generally, check valves have sealing parts of different shapes such as gates, balls, diaphragms, discs, etc. The greater the downstream pressure, the better the sealing effect of the check valve.

What are the types of check valves?

Spring check valve, swing check valve, lift check valve,flap check valve, wafer check valve

Spring check valve

Spring-loaded check valves are divided into spring-loaded linear check valves and spring-loaded y-check valves.

Spring-loaded linear check valves

Spring check valves are common, simple in design and easy to install. Figure 1 shows the spring check valve in the open and closed positions. Arrows indicate the direction of fluid flow. When fluid enters the valve inlet, enough pressure is generated to compress the spring and push the valve disc, opening the valve and allowing fluid to pass through the valve. When the input pressure is less than the spring force or there is sufficient negative pressure, the negative pressure and spring rebound force push the valve disc back to its original position, and the valve automatically closes. The short travel of the spring and disc allows for a fast closing response time. The only drawback to this design is that the spring check valve is affected by spring force. When the spring works for some time, the rebound time of the spring will be extended and the rebound amplitude will become smaller, thus affecting the performance of the valve in the pipeline.
Spring check valves can be installed horizontally or vertically.

Spring check valve working flow chart

Figure 1:Spring-loaded check valve open (left) and closed (right).The working components are the valve body (A), disc (B), spring (C), and guide (D)

Spring-loaded Y-check valve

The working process of the spring-loaded Y-shaped check valve is similar to that of the spring-loaded check valve. The difference is that the spring and valve disc are fixed on one side of the valve body at a 45-degree angle, forming a Y shape. Y-shaped check valves require more installation space. When the valve’s spring fails, the Y-shaped valve can replace the spring.

Spring-loaded Y-check valve

Figure 2:Spring-loaded Y-check valve

PVC True Union Ball Check Valve

PVC True Union Ball Check Valve

CPVC Single Union Ball Check Valve

CPVC Single Union Ball Check Valve

Swing check valve

The swing check valve consists of a rocker arm mechanism and a sealing disc. It is also called a “swash plate” or “baffle” check valve. They have a disc on their hinge (or trunnion) that opens under inlet pressure. When the inlet pressure decreases or backflow occurs, the valve disc will automatically close under the action of gravity. Figure 3 shows the working flow of the swing check valve.

Swing check valve Working diagram

Swing check valve Working diagram

Flap check valve

The lift check valve consists of a fixed guide device and a valve disc. There is sufficient pressure at the valve inlet to force the valve disc to rise (lift) away from the valve seat to allow the medium to flow. It requires opening pressure to overcome gravity and/or spring resistance. Guides hold the disc in vertical line for reseating with proper alignment and sealing.

Working diagram of lift check valve

Figure 3: Working diagram of lift check valve

Flap check valve

The flap check valve is composed of a rocker arm mechanism and a sealing disc. When the fluid flows into the valve, sufficient pressure is generated to push the flap to open. When the pressure at the inlet of the pipeline is lower than the pressure at the outlet, the sealing valve will automatically close due to gravity to prevent backflow.

Flap check valve

Figure 4: Working diagram of flap check valve

Wafer check valve

The internal design of the wafer check valve consists of a rocker arm mechanism and a sealing disc. When there is sufficient opening pressure in the pipeline, the valve starts to work, allowing the medium to flow through the valve. When the opening pressure in the pipeline is insufficient or there is negative pressure, the valve will automatically close due to gravity. The wafer check valve cannot be installed directly on the pipeline and requires two flanges to be fixed on the pipeline.

UPVC Wafer check valve

UPVCWafer check valve

How to choose a check valve?

There are several factors to consider when choosing the right check valve:
1. Fluid properties: The selection of check valve should be determined according to the properties of the fluid, such as liquid, gas or steam, etc. Different fluids have different requirements for valve materials and sealing.
2. Working pressure: Determine the required rated pressure of the valve based on the working pressure of the pipeline system.
3. Flow requirements: Select the appropriate valve type and size according to the flow requirements of the system.
4. Temperature requirements: Select the appropriate valve material according to the operating temperature of the system to ensure that the valve can work normally in high or low temperature environments.
5. Installation requirements: Select the appropriate valve connection method according to the installation requirements of the system, such as flange connection, threaded connection or welded connection, etc.
6. Economy: Choose a suitable check valve based on budget and economic considerations, taking into account factors such as the valve’s price, maintenance costs, and lifespan.

What materials are check valves made of?

Most check valves are made of durable materials that can withstand a certain amount of pressure and are corrosion-resistant. Common check valve materials include: PVC, CPVC, PPH, Brass,carbon steel, stainless steel, copper, and ductile iron,and cast steel.

PVC: PVC is corrosion-resistant and inexpensive. The smooth surface of PVC allows the check valve components to move easily. PVC check valves are usually used in water supply, irrigation, sewage treatment and chemical media transportation.
CPVC: CPVC has better corrosion resistance and higher working temperature than PVC, and the price is slightly higher than PVC. CPVC material check valves are usually used in water supply, irrigation, sewage treatment and chemical media transportation.

PPH: PPH has excellent chemical resistance, wear resistance, high temperature resistance, corrosion resistance, aging resistance and good insulation. PPH materials are widely used in chemical media transportation, food, medicine, sewage treatment and other fields.
Brass: It has excellent machining properties and does not rust. It is more expensive than other materials and is generally used for water supply pipes.
Carbon steel: has excellent properties of resistance to high temperature and pressure, and is easy to rust.
Ductile Iron: Ductile iron contains more than 3% carbon, which gives it excellent machinability and can be bent and formed easily. It is resistant to high temperatures and pressures and is generally used in urban water supply or drainage main pipeline systems.
Stainless Steel: Stainless steel is corrosion-resistant, durable and can be used in harsh conditions, including chemical applications.
Cast steel: Cast steel is used to produce check valves because it can resist sudden impacts, does not deform, break, bend, and can withstand high temperatures and pressures. Widely used in steam and water medium pipelines under various working conditions and medium pipelines in petroleum, chemical industry, metallurgy, etc.

What are the advantages of check valves?

Prevent Backflow: Check valves are designed to allow fluid to flow in only one direction and block reverse flow, preventing backflow when pressure drops or the pump shuts down. This helps protect the system from contamination and water hammer damage to the equipment.
Reduces water hammer: Water hammer is the sudden pressure surge that can occur when the flow of water suddenly stops, and check valves help reduce water hammer by preventing the flow of water from reversing.
Reduced Maintenance Costs: A check valve is a simple device that reduces maintenance on your piping system.
Reduce production costs: reduce downtime and production losses.

What are the applications of check valve?

The check valve is one of the essential valves in the pipeline and is a safety device in the pipeline system. Installing check valves in pipelines can reduce maintenance time and reduce production costs. Therefore check valves are widely used in:
water supply system
Irrigation system
sewage treatment
pharmaceutical
Petroleum and natural gas

What are common check valve problems?

Common problems with check valves include leakage, component wear, backflow, water hammer, and noise.

Leo Xiong

     I am the author of this article and the CEO and Marketing Director of SWDPLASTIC with 15 years of experience in the valve and pipeline industry. If you have any questions, you can contact me anytime.

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