Where Should The Check Valve And Backflow Preventer Be Installed? Did You Pretend It Right?

Where should the check valve and backflow preventer be installed? Did you pretend it right?

1. Definition

1. Check valve

Check valves are used to prevent the reverse flow of water. Check valves mainly have two types: lift type and swing type. The lift check valve is installed on the horizontal pipeline, and the head loss is large, which is only suitable for small pipe diameters. Swing check valves are generally larger in diameter and can be installed on horizontal and vertical pipelines. The installation of the above two kinds of check valves has directionality. The opening and closing of the valve plate or spool must be consistent with the direction of water flow, and it must be automatically closed under the action of gravity to prevent the normally open state.

2. Backflow preventer

The backflow preventer (also known as the anti-fouling shutoff valve) consists of two check valves with a drain valve between them, which is used to prevent backflow pollution in the drinking water pipeline. The difference between the backflow preventer and the check valve is that the check valve is only a valve that guides the water flow in one direction, not an effective device to prevent backflow pollution. The pipeline backflow preventer has the function of a check valve. After the pipeline backflow preventer is installed, it is not necessary Set the check valve again.

2. the selection requirements of the check valve

1. Many comprehensive factors should be considered when choosing a check valve type:

(1) The opening pressure of the check valve is related to the sealing performance of the check valve in the closed state. If the closed state has a good sealing performance, the opening pressure will be large, and vice versa.

(2) The opening pressure is generally greater than the local head loss when the water flows normally after opening.

(3) The quick-closing noise-closing check valve and the damping slow-closing check valve have the function of weakening the pump-stop water hammer, but the mechanism of the two attenuating the pump-stop water hammer is different, and the quick-closing noise-closing check valve is general Used for small diameter water pump, damping slow closing check valve is generally used for large diameter water pump.

(4) When the water flow stops, the disc or spool of the check valve should be able to close automatically under the action of gravity or spring force. Generally speaking, horizontal lift check valves, damping slow-closing check valves and multifunctional valves can only be installed on horizontal pipes. Except for vertical lift check valves, other check valves can be installed on horizontal pipes. Up or on a riser with a bottom-up flow direction. The standpipe with the water flow direction from top to bottom should not be equipped with a check valve.

2. The valve type selection of the check valve should be determined according to factors such as the installation position of the check valve, the water pressure before the valve, the sealing performance requirements after closing and the size of the water hammer caused by closing, and should meet the following requirements:

(1) For parts with low water pressure in front of the valve, swing, ball and prismatic check valves should be selected.

(2) For parts with tight airtight performance requirements after closing, a check valve with a closing spring should be selected.

(3) For parts that require weakening and shutting off the water hammer, quick-closing muffler check valves or slow-closing check valves with damping devices should be selected.

(4) The disc or spool of the check valve should be able to close by itself under the action of gravity or spring force.

(5) The minimum pressure of the pipe network or the minimum water level of the water tank should be able to automatically open the check valve.

3. The determination of setting the check valve pipe section

1. The check valve is only a valve that guides water flow in one direction, not an effective device to prevent backflow pollution.

The pipeline backflow preventer has the function of a check valve, but the check valve does not have the function of a pipeline backflow preventer, so after the pipeline backflow preventer is installed, there is no need to install a check valve.

When the inlet and outlet pipes of the water tank and water tower are one, in order to prevent water from entering at the bottom, a check valve should be installed on the pipe section where the water is discharged at the bottom. , Make the check valve in a state of unstable pressure, which will cause the disc (core) to vibrate. Therefore, the check valve should be subjected to vibration isolation treatment, and it is not suitable to choose a swing or lift check valve with large vibration.

2. Check valves should be installed on the following pipe sections of the water supply pipe section:

(1) Check valves should be installed on the inlet pipes directly connected to the community or buildings from the urban water supply network.

(2) A check valve should be installed on the inlet pipe of a closed water heater or water equipment.

(3) A check valve should be installed on the outlet pipe of each water pump.

(4) Check valves should be installed on the water tank, water tower, and highland pool where the inlet and outlet pipes share the same pipeline.

4. Where should the check valve be installed?

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

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.

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.

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 the 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 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.

5. Necessity of installing backflow preventer on water supply pipeline

Since most cities usually only build a water supply network, in addition to the main supply of domestic water, it also supplies non-domestic drinking water in terms of fire-fighting water, industrial water, and green water. Therefore, non-domestic drinking water needs to be connected from the domestic drinking water pipeline. Water pipes.

However, non-drinking water pipelines are polluted due to long-term use or contact with the environment during use. Once backflow occurs, the drinking water pipeline network may be seriously polluted. Regardless of whether the water in the non-domestic drinking water pipeline connected to the drinking water pipeline has been polluted, as long as it flows back into the drinking water pipeline, it is called backflow pollution. For the above reasons, pollution devices to prevent backflow must be installed on the water supply pipeline.

6. The pipe section where the backflow preventer should be installed

1. When the following water pipes are directly supplied from drinking water pipes, backflow preventers should be installed at the following locations of these water pipes:

(1). Two or more inlet pipes are connected from different pipe sections of the urban water supply pipe network, and the community or building that forms a loop pipe network with the urban water supply pipe is on the inlet pipe;

(2) On the suction pipe of the pump that directly pumps water from the urban domestic water supply pipe network;

(3) When the water pressure of the urban water supply network is used and the introduction pipe of the community has no backflow prevention facilities, it is used to inject water into the water inlet pipe of commercial boilers, hot water units, water heaters, air pressure tanks and other pressure vessels or closed vessels;

2. When connecting to the following water pipes or equipment from the drinking water pipeline system in the community or building, a backflow preventer should be installed:

(1) When the fire-fighting water pipeline is separately connected, it shall be at the beginning of the fire-fighting water pipeline;

(2) On the outlet pipe of the fire water pump pumping water from the drinking water storage tank.

3. When the drinking water pipeline system is connected to the following hazardous and toxic places or equipment containing substances harmful to health, a backflow preventer should be installed:

(1) On the connecting pipes of storage tanks (tanks), devices and equipment;

(2) In addition to setting up in accordance with paragraph (1) of this article, chemical agent tank farms, chemical workshops, and laboratory buildings (medicine, case, biochemical), etc., air gaps should also be set on their introduction pipes.

4. When connecting to the following water pipes from the drinking water pipeline system in the community or building, vacuum breakers should be installed on these water pipes:

(1) When the air gap between the outlet of the water filling or replenishing pipe of the swimming pool, water amusement pool, massage pool, water feature pool, circulating cooling water collection pool and the overflow water level is less than 2.5 times the diameter of the outlet pipe, it shall be filled (Make up) on the water pipe;

(2) For green sprinkler irrigation systems that do not contain chemicals, when the sprinkler is underground or automatic lifting type, at the beginning of the pipe; (4) Fire (hose) reel;

(5) The connection between the flush nozzle of the outlet hose and the water supply pipe.

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