Selection, Location, Advantages and Disadvantages of Valves in Water Supply Pipeline

Valve selection and setting position
(1) The selection principle of valves used on water supply pipelines
1.Pipe diameter is not greater than 50mm, it is appropriate to use the globe valve, pipe diameter is greater than 50mm, use gate valve, butterfly valve;
2.Regulating valve and globe valve should be used to adjust flow and water pressure;
3.The part requiring small water flow resistance (such as the water pump suction pipe) should use gate valve;
4.Gate valve and butterfly valve should be used on the pipe section where the water needs to flow bidirectional, and globe valve should not be used;
5.Butterfly and ball valves should be used for parts with small installation space;
6. It is appropriate to use a globe valve on the pipe section that is often opened and closed;
7. Multifunctional valve should be used on the outlet pipe of the large caliber water pump.
(2) The position of valves on the water supply pipeline
1.The water supply pipeline of the residential district is from the entrance pipe section of the municipal water supply pipeline;
2.The nodes of the outdoor annular pipe network in the residential community should be set according to the separation requirements. When annular pipe section is too long, it is appropriate to set up a segmented valve;
3.Start of branch pipe or household pipe from the water supply main pipe in the residential district;
4.Household pipe, water meter and each branch riser (bottom of riser, upper and lower end of vertical ring pipe network riser);
5.Branch pipe of loop pipe network, connecting pipe of through branch pipe network;
6.Indoor water supply pipeline to households, public toilets and other access to the water distribution pipe starting point, When there are 3 or more water distribution points on the water distribution branch pipe;
7.Outlet pipe of pump, suction pump of self-irrigation pump;
8.Water tank inlet, outlet pipe, drainage pipe;
9.Water filling pipe for equipment (such as heater, cooling tower, etc.);
10.Water distribution pipe for sanitary appliances (such as urinals, washbasins, showers, etc.);
11.Before some accessories, such as automatic exhaust valves, pressure relief valves, water hammer eliminators, pressure gauges, sprinklers, etc., before and after the pressure reducing valve and backflow preventer, etc;
12.The lowest part of the water supply network should be equipped with a drain valve.

 

(3) The selection of check valve
Check valves should generally be selected according to their installation position, water pressure before the valve, sealing performance requirements after closing and the size of the water hammer caused by closing factors:
1.Swing type, ball type and shuttle type check valves should be selected when the water pressure before the valve is small;
2.When the sealing performance is strict after closing, a check valve with a closing spring should be selected;
3.When the water hammer is required to be weakened and closed, Quick closing silencing check valve or the Dashpot check valve with damping device should be selected;
4.The disc of the check valve should be able to close itself under the action of gravity or spring force.
(4) Set check valves in water supply lines
Service pipe; On the inlet pipes of sealed water heaters or water installations; On the water pump outlet pipe; The inlet and outlet pipes are combined on the water tank, water tower and outlet pipe section of the highland pool.
Note: No check valve is required for pipe sections equipped with pipe backflow preventers.

 

(5)Position of exhaust device for water supply pipe
1.Automatic exhaust valves shall be installed at the ends and highest points of intermittently used water supply networks;
2.Pipe section of water supply network with obvious undulating air accumulation. Automatic exhaust valve or manual valve has been installed at the peak point of this section for exhaust;
3.Pneumatic water supply device, when the use of automatic air tank, the highest point of the water distribution network should be equipped with automatic exhaust valve.

Advantages and disadvantages of various valves
1.Gate valve
Gate valve refers to the closing part (gate plate) along the vertical direction of the channel axis of the valve, mainly used as a cutting medium on the pipeline, that is, fully open or fully closed. Generally, gate valves cannot be used to regulate flow. It can be applied to low temperature pressure can also be applied to high temperature and high pressure, and according to the different materials of the valve. But gate valves are generally not used for conveying mud and other media in the pipeline
Advantages:
(1)Low fluid resistance;
(2)Smaller torque required for opening and closing;
(3) It can be used in the loop network where the medium flows in two directions, that is to say, the flow direction of the medium is not restricted;
(4) When fully opened, the erosion of the sealing surface by the working medium is smaller than that of the globe valve;
(5) The body structure is relatively simple, and the manufacturing process is better;
(6) The structure length is relatively short.
Disadvantages:
(1)Larger dimensions and opening height, larger installation space required;
(2)In the process of opening and closing, the friction loss of sealing surface is larger, even at high temperature easy to cause chafing phenomenon;
(3) General gate valves have two sealing covers, which increase some difficulties for processing, grinding and maintenance;
(4) Long opening and closing time.

2. Butterfly valve:
Butterfly valve is a kind of valve that opens, closes and adjusts the fluid channel by reciprocating rotation of disc type open and close parts about 90 °.
Advantages:
(1) Simple structure, small size, light weight, material saving;
(2) fast opening and closing, small flow resistance;
(3) Can be used for medium with suspended solid particles, according to the strength of the sealing surface can also be used for powder and granular medium. It can be used for bidirectional opening and closing and adjustment of ventilation and dust removal pipeline, widely used in metallurgy, light industry, electric power, petrochemical system of gas pipelines and waterways, etc.
Disadvantages:
(1) The flow adjustment range is not large, when open up to 30%, the flow will enter more than 95%;
(2) Due to the structure and sealing material of the butterfly valve, it is not suitable for high temperature and high pressure pipeline system. General operating temperature below 300℃, PN40 below;
(2) The sealing performance is poor compared with ball valves and globe valves, so it is used in places where the sealing requirements are not very high.

3. Ball valve
Ball valve is evolved from the plug valve, its opening and closing parts is a ball, using the ball around the axis of the stem rotation 90 degrees to achieve the purpose of opening and closing. Ball valve in the pipeline is mainly used to cut off, distribution and change the direction of media flow, designed into the V-shaped opening ball valve also has good flow control function.
Advantages:
(1) Has the lowest flow resistance (actually 0);
(2) Because it is not stuck in the work (in the absence of lubricant), it can be reliably applied to corrosive media and low boiling point liquid;
(3) In the larger pressure and temperature range, can achieve complete seal;
(4) It can realize fast opening and closing, and the opening and closing time of some structures is only 0.05~0.1s, so as to ensure that it can be used in the automation system of the test bench. Quickly open and close the valve, operation without impact;
(5) Spherical closing parts can be automatically positioned on the boundary position;
(6) The working medium is sealed reliably on both sides;
(7) When fully open and fully closed, the sealing surface of the ball and seat is isolated from the medium, so the medium passing through the valve at high speed will not cause erosion of the sealing surface ;
(8) Compact structure, light weight, it can be considered to be the most reasonable valve structure for low temperature medium system;
(9) Symmetrical valve body, especially welded valve body structure, can withstand the stress from the pipe;
(10) Closing parts can withstand the high pressure difference at closing.
(11) The ball valve of the fully welded valve body can be buried directly underground, so that the valve internals are not eroded, and the maximum service life can reach 30 years. It is the most ideal valve for oil and gas pipelines.
Disadvantages:
(1) Because the main valve seat sealing ring material is PTFE, it is inert to almost all chemical substances, and has a comprehensive characteristics of small coefficient of friction, stable performance, not easy to aging, a wide range of temperature and excellent sealing performance. However, the physical properties of teflon, including high coefficient of expansion, sensitivity to cold flow and poor thermal conductivity, require that the seat be designed around these characteristics. Therefore, when the sealing material hardens, the reliability of the seal is compromised. Moreover, PTFE temperature resistance grade is low, can only be used under the condition of less than 180℃. Above this temperature, the sealing material will age. In the case of long-term use, it is generally used at 120℃.
(2) Its regulating performance relative to the globe valve is worse, especially the pneumatic valve (or electric valve).

4. Globe valve
It refers to the valve that the closing part ( disc ) moves along the center line of the valve seat. According to this movement of the valve disc, the change of the valve seat opening is proportional to the valve disc stroke.Because this kind of valve stem opening or closing stroke is relatively short, and has a very reliable cutting function, and because the change of the valve seat opening is proportional to the stroke of the valve disc, it is very suitable for flow regulation.Therefore, this type of valve is very cooperative for cutting or regulating and throttling.
Advantages:
(1) In the opening and closing process, because the friction between the disc and the valve body sealing surface is smaller than the gate valve, so it is wear-resistant;
(2) The opening height is generally only 1/4 of the valve seat channel, so it is much smaller than the gate valve;
(3) Usually there is only one sealing surface on the valve body and valve disc, so the manufacturing process is better and easy to maintain;
(4) Because its filler is generally a mixture of asbestos and graphite, so the temperature resistance grade is higher. General steam valves use globe valves.
Disadvantages:
(1) because the medium through the valve flow direction has changed, so the minimum flow resistance of the stop valve is higher than most other types of valves ;
(2) Due to the long stroke, the opening speed is slower than the ball valve.

5. Plug valve
It is a kind of valve that the closing part is a plunger-shaped rotary valve, and the channel port on the valve plug is connected or separated from the channel port on the valve body through 90 ° rotation to realize opening or closing. The shape of the valve plug can be cylindrical or conical. Its principle is basically similar to the ball valve. The ball valve is developed on the basis of the plug valve. It is mainly used for oilfield exploitation and also for petrochemical industry.

6. Safety valve
It refers to the overpressure protection device on the pressure container, equipment or pipeline. When the pressure in the equipment, container or pipeline rises above the allowable value, the valve opens automatically and then discharges in full to prevent the pressure of the equipment, container or pipeline from continuing to rise ; when the pressure is reduced to a specified value, the valve should be automatically closed in time to protect the safe operation of equipment, containers or pipelines.

7. Steam trap valve
In conveying steam, compressed air and other media, there will be some condensed water formation, in order to ensure the work efficiency and safe operation of the device, we should discharge these useless and harmful media in time to ensure the consumption and use of the device. It has the following functions :
(1) It can quickly eliminate the condensation water ;
(2) to prevent steam leakage ;
(3) Exclude air and other non-condensable gases.

 

8. Pressure reducing valve
It is a valve that reduces the inlet pressure to a required outlet pressure by adjustment, and relies on the energy of the medium itself to keep the outlet pressure automatically stable.

9. Check valve
The check valve is an automatic valve, which is automatically opened and closed by the force generated by the flow of the medium itself in the pipeline. Check valve is used in pipeline system, its main function is to prevent medium backflow, prevent pump and drive motor reversal, and the leakage of container medium. Check valves may also be used to supply auxiliary systems where pressure may rise above the system pressure. It can be mainly divided into a swing type ( rotating according to the center of gravity ) and a lift type ( moving along the axis ).