In this article, you are going to learn about different types of valve symbols used in P&ID. Many types of valves are used in process piping and each has a different symbol. This makes the valve one of the tricky parts of reading P&ID. But with practice, you can easily remember these symbols and can read P&ID effectively.

There are two types of valve symbols — first, generic symbols, and second, a symbol with a modifier. Generic symbols will tell you that there is a valve in the line, but it will not tell you about the types of the valve. Whereas the valve symbol with modifier will tell you the exact type of valve that is used in the pipeline.

Generic symbols of Valves

Valve Symbols for 3 way and 4 way valve

Here in the image above, you can see commonly used symbols for valves. These symbols are generic in nature — for example, the first symbol of a valve.

Now when you look at the symbol on drawing, it just gives you an indication that some kind of valve is used, but it will not provide you with information about the type of valve whether it is a gate, globe, or plug type valve. There are dedicated symbols for a gate, globe, plug, ball valves which I will explain to you in minutes.

Similarly, the next two symbols are for three-way and four-way valve. It can be a plug or ball valve. Subsequent two symbols are of a check valve and stop check valve. These check valves can be swing check or lift check valve.

The next symbol is the excess flow valve. You can see that it is the same as a check valve with the only difference is the written text, below the valve symbol. You have to be very careful while reading this type of symbol as it can easily overlook.

The last symbol is of automatic recirculation valve. This type of valve is used in the pump discharge line to ensure the pump will not suffer from low inlet pressure which leads to cavitation.

Watch this video which will explain to you all aspects covered in this article.

How to Read PID Course

Relief Valve Symbols

relief valve Sysmbol

Here in the image above, the first symbol is of angle valve. In most cases, a globe valve is used as an angle valve. The next symbol is of relief valve that used to protect the piping system or equipment from overpressure.

Now the breather valve is used on the cone roof tank. This valve serves the function of the relief valve and vacuum valve. In the event of over-pressure, this valve release the pressure, and in case a vacuum is created in the tank, this valve allows air to enter the tank. Just like breathing air in and out.

The vacuum valve prevents damage to the equipment from negative pressure. Pilot operated relief valve are just working as a relief valve, but are used for large size piping. In this type, a small relief valve is used to operate the main relief valve. This arrangement is cost-effective in the large size relief operation.

Now I will explain to you the specific valve symbol that used in P&ID and isometric drawings.

If you want to learn about more than 18 types of valves in detail, you can buy my course, how to be an expert in piping valves.

Piping Courses

Gate Valve Symbol

Gate valve symbol

In the image above, you can see the gate valve. Now see the P&ID symbol for the gate valve. It is a modification of a generic valve symbol by inserting a vertical line between two triangles. Three symbols shown below are the gate valve symbols used in isometric drawings. The first is for butt-welding ends, second is for flanged end valve and the third one is for socket end connection.

Globe Valve Symbol

Globe Valve Symbol

For a globe valve, a symbol is modified by adding a small dark circle between triangles. You can see that P&ID and isometric symbols are almost the same with the only change in end types.

Ball Valve Symbol

Ball Valve symbol

You can see that there are two P&ID symbols for a ball valve. The reason is that P&ID and isometric drawing symbols are changed from company to company. So if you switch the company, you should be aware of this. Similarly, you can see the ISO symbols for butt, flanged and socket ends ball valve.

Needle Valve Symbol

needle valve Symbol

Same as a ball valve, a needle valve also has multiple P&ID symbols. If you can see that even these symbols are different but still you can easily interpret. If you are using second P&ID symbols, your isometric symbol will be changed accordingly.

Plug Valve Symbol

Plug Valve symbol

For the plug valve, the first symbol is a bit confusing with a globe valve. If you remember the symbol of a globe valve, it has a dark circle in between the triangle, whereas here only circle outline is there. So when you see this type of symbol, better to double check the drawing.

Butterfly Valve Symbol

Butterfly valve symbol

Butterfly valve symbol is the only symbol where a full triangle is not used. If you refer to the first symbol, it is similar to a globe valve but a triangle is not full. The alternative symbol is clearer in this case. For isometric symbols, you can see that there is no socket end butterfly valve.

Diaphragm Valve Symbol

diaphragm valve symbol

Here is the diaphragm valve. There is no butt-welded diaphragm valve available. Most diaphragm valves are flange type and they are used to handle process media with solid particles.

Special Valve Symbol

P&ID valve symbols for generic type

In the image above, you can see the symbols with a special note. The first symbol is a special valve. The word NC return below the second symbol is more important. It indicates that this valve remains closed during normal operation. Now the next two symbols are also used alternatively to show the valve position during normal operation.

The last symbol used to show the pressure end of the valve. The shaded are showing the pressure side of the valve.

This is all about P&ID and isometric symbols of Valves. If you want to learn about equipment symbol that uses in drawing check this article. 

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