Check valve applications and materials.

The check valve is a kind of automatic valve, its role is to ensure the directional flow of media in the pipeline without backflow. It is an essential working part of the pipeline system, and for different fluid media, we have to choose different valves.

Working pressure:
Its working pressure1 is .0~25MPa/Class150-2500/2.0-42.0MPa Working temperature -29~+550℃.

Common materials:
Common check valve materials usually include. WCB, HT200, HT250, QT350, QT450, WC6, WC9, CN7M, CF8 (M), CF3 (M). A105, F304 (L), F316L, etc.
Used for pipelines under various working conditions in petroleum, chemical, pharmaceutical, fertilizer, electric power, and other industries. Applicable media are water, oil, steam, acidic media, etc.

Check valve classification:

1.The valve body shape of the lift check valve is the same as the stop valve (which can be used in common with the stop valve), its sealing performance is good, and the fluid resistance coefficient is large. The horizontal check valve should be installed on the horizontal pipeline and the vertical one on the vertical pipeline.

Ductile Iron Ball Check Valve

2. Swing check valve, the valve disc rotates around the pin shaft outside the valve seat, which is more common. The valve can be installed in any position. It can be installed in horizontal, vertical, or inclined pipelines. If installed on a vertical pipeline, the direction of flow of the medium should be bottom-up.

British Standard Swing Check Valve

3.The disc of the disc check valve rotates around the pin shaft in the valve seat. Its structure is simple, the sealing performance is poor, and the installation position is not restricted. It can be installed in a horizontal pipeline, or in a vertical or inclined position.

the disc check valve

4.

PVC-Swing-check-valve

Flip check valve

The flip check valve is made of all plastic material, smooth, lightweight, anti-oxidation, anti-corrosion, and erosion resistance.
The overall structure is simple and compact, beautiful in appearance, short disc stroke, and small valve closing impact.

5. True Union Check Valve
The valve is made of all plastic material, exquisite appearance, smooth surface, fine processing, full flow design, no rust, and corrosion resistance. When assembling the valve, no silicone oil lubricant is used, which is hygienic and non-toxic and can be applied to most media.
The design of a two-way dual-router is convenient for maintenance, and the ball valve can be closed and the router can be unloaded to carry out the repairing of the latter section without the need to stop the equipment pipeline in the front section.

UPVC True Union Ball Check Valve

UPVC True Union Ball Check Valve

How to choose a check valve at different pressures

Size Pressure Model
<DN50MM high and medium pressure check valve vertical lift check valve and straight-through lift check valve
<DN50MM low and medium pressure check valve butterfly check valve, vertical lift check valve, and diaphragm check valve
50mm<DN<600mm High and medium pressure check valve Swing check valve Medium and low-pressure check valve
200mm<DN<1200mm Medium and low-pressure check valve Wear-free spherical check valve
500mm<DN<1200mm low-pressure check valve butterfly check valve and diaphragm check valve

1.Selection and installation of pump outlet check valve 

① Swing check valves are generally installed on horizontal pipelines: For check valves with a diameter of DN~80mm, they can also be installed on vertical or upwardly inclined pipelines.
② The straight-through lift check valve should be installed on the horizontal pipeline; the vertical lift check valve must be installed on the vertical pipeline, and the medium flows from bottom to top.
③ As the check valve is easily damaged, a check valve should be installed near the pump outlet, and a shut-off valve (usually a ball valve or gate valve) should be installed on the top of the check valve to facilitate maintenance.
④ In order to facilitate the pressure relief before the check valve is disassembled, if the check valve itself does not have a drain valve, a pressure relief valve should be installed between the check valve and the shut-off valve.

Protective measures against water hammer damage to the sealing surface of check valves

The setting of the check valve plays a role in preventing the material from flowing back and preventing the pump impeller from being hit by liquid. But as far as the check valve itself is concerned, the improper setting will cause a sudden impact of the valve disc on the valve seat caused by the water hammer, which will damage the sealing surface of the check valve. Therefore, several protective measures should be taken.

Protection measures:
1. For the swing check valve with DN>80mm at the pump outlet, the horizontal installation method should be adopted to reduce the disc return and impact.

2. For pipelines with a pump outlet check valve diameter DN≥150mm, bypass should be installed before and after the check, valve to prevent excessive pressure rise in front of the valve and damage to the sealing surface of the valve.

3. For pipelines with high pressure at the start and end of the pump discharge pipeline, if the bypass is not allowed, the following measures can be taken.
① Set a safety valve to replace the bypass valve. Its function is similar to the bypass valve. It is set near the outlet of the check valve. When the pressure rises due to the water hammer, a part of the water can be released to prevent damage caused by the continued increase in pressure.

4. In-line check valve: a valve whose disc slides along the centerline of the valve body. The pipeline check valve is a new type of valve, its small size, Lighter weight, and good processing technology are one of the development directions of check valves. However, the fluid resistance coefficient is slightly larger than that of the swing check valve.

Installation Notes:

1. Do not allow the check valve to bear weight in the pipeline. Large check valves should be independently supported so that they are not affected by the pressure generated by the piping system.
2. When installing, pay attention to the direction of medium flow should be consistent with the arrow direction of the valve body.
3. Lifting vertical flap check valve should be installed on the vertical pipeline.
4. Lifting horizontal flap check valve should be installed on the horizontal pipeline

The  valve installation position

The valve is installed to ensure the flow direction of the water inside the pump, so as to ensure the normal operation of the pump. Therefore, the installation position of the valve, whether it is installed before or after the pump, can be divided into two situations.

A.One is to install at the end of the vertical suction pipe in front of the water pump.

The purpose is to fill the water pump without pumping water once because when there is no water in the water pump and the suction pipe in front of the pump, the water pump can only run idling and cannot pump water, so the water pump must The water can only be pumped out when it is full of water. The installation of this pump is a method when it is above the liquid level. It is also called a negative pressure method, such as pumping water up from a well.

B.Another way to install the pump is that the liquid level is higher than the pump.

This method is generally used for secondary water supply. Because the liquid level is higher than the pump, it is not necessary to close the pump outlet valve when starting and stopping the pump, so the check valve should be installed in The rear of the water pump.

Cautions:

The valve must be installed at the outlet of the pump and before the outlet control valve in order to check the check valve. Generally, the outlet of the pump is the soft connection (shock absorber) first, followed by the check valve, and then the isolation valve (such as butterfly valve, gate valve, stop valve, etc.).

1. Install the check valve first and then the gate valve or butterfly valve
Advantages: It can protect the check valve, especially in parallel pumps. When one pump does not start and the other pump starts, the impact force is borne by the gate valve or butterfly valve
Disadvantages: Who will protect the gate valve or the check valve? There was a case where the valve plate of a butterfly valve was broken.
2. Install gate valve or butterfly valve first and then check valve
Advantages: It can protect the butterfly valve or gate valve, and the impact force is borne by the check valve
Disadvantages: Who will protect the check valve? The check valve is switched on and off by the pressure difference. If the pressure of the main pipe is high, it will be closed, and the pressure of the pump will be opened. If the flow rate used is unstable, the check valve will switch repeatedly. Affect the life of the check valve.

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