The reliability of the safety valve action is directly related to boiler safety and personal safety. The correct selection of the safety valve according to the working conditions of the boiler is a prerequisite for whether the safety valve can play a role in safety protection.

Therefore, the correct selection of industrial boiler safety valve is very important.

The correct selection of safety valves involves two aspects: one is the action characteristics and parameters of the safety valve itself;

On the one hand, it is the working conditions of the boiler, in other words: what kind of working conditions does a certain type of safety valve apply to the boiler; and which type of safety valve should be selected for the boiler under certain working conditions.

The practice of boiler inspection and safety valve verification work shows that only when both are considered can the safety valve be selected correctly.

The following are the key points for selecting safety valves for industrial boilers from the two aspects of safety valves and boilers.

Safety Valve Performance and Selection

Three types of spring safety valves commonly used in industrial boilers:

The first model: A48Y-1.6C. Among them: A-safety valve; 4-flange connection; 8-spring type not closed with wrench full open type; Y-seat sealing surface material is hard alloy; 1∙6-nominal pressure is 1∙6MPa;

The second model: A47H-1.6. Among them: A-safety valve; 4-flange connection; 7-spring type non-closed with wrench micro-opening type; H-seat sealing surface material is alloy steel; 1∙6-nominal pressure is 1∙6MPa;

The third model: A27T -1.0. Among them: A—safety valve; 2—external thread connection; 7—spring type non-closed with wrench micro-opening type; T—valve seat sealing surface or lining material is copper alloy; 1.0—nominal pressure is 1.0MPa;

1.The full opening safety valve is suitable for steam boilers, and the micro opening safety valve is suitable for hot water boilers, and it is not suitable to exchange between the two

The main reason is: the opening height of the disc of the full-opening safety valve is equal to or greater than 1/4 of the diameter of the flow channel, and it is of the sudden opening type, that is, when the pressure rises little, the disc suddenly opens to discharge the medium. It has the advantages of sensitive action, large discharge volume and quick seat return.

In addition, the volume of the lower valve body of the full-opening safety valve is larger than that of the micro-opening type, and its outlet diameter is also an order of magnitude larger than the inlet diameter, which meets the needs of steam volume expansion when the safety valve is discharged, so it is suitable for steamer.

The height of the valve disc of the micro-opening safety valve is only 1/40 to 1/20 of the diameter of the flow channel. The main feature of the action of the micro-opening safety valve is that the valve disc has no sudden opening and closing action in the process of opening and returning to the seat. That is, the opening height of the valve disc increases with the increase of the inlet medium pressure, which belongs to the proportional action safety valve.

Its advantage is that the pressure of the protected system will not cause drastic changes due to the opening and reseating action of the safety valve. Due to the small opening height of the safety valve, the discharge volume is smaller than that of the full-opening safety valve of the same caliber, and the volume of the lower valve body is relatively small, and the inlet and outlet diameters are the same, so it meets the need for no volume expansion. So it is only suitable for hot water boilers.

If the full opening safety valve is installed on the hot water boiler, water impact will easily occur when the safety valve is opened or returned to the seat;the pressure of the boiler will continue to rise, and the protective effect of the safety valve cannot be brought into play. To ensure sufficient discharge, it is necessary to increase the diameter of the safety valve inlet pipe and the nominal diameter of the safety valve, which is obviously uneconomical and unsafe.

2.Generally, hammer type and lever type safety valves are not used

This is mainly due to the following disadvantages in the structure of the hammer type and lever type safety valves: the valve body is bulky, sensitive to vibration, easy to eccentric, poor seat return performance, etc. In use, there are many examples of accidents caused by the deficiency of its structure. During boiler inspection and safety valve calibration work, it was found that some safety valve manufacturers (especially some small factories) produced poor quality products, used materials that did not meet the requirements of national standards, cut corners and did not play a role in safety protection.

Matching selection of boiler and safety valve

1.Determine the nominal pressure of the safety valve according to the working temperature and working pressure of the boiler

Under the same nominal pressure, when the working temperature increases, the maximum working pressure decreases accordingly, which is the so-called "long-term temperature-lowering principle". Since the general working temperature of industrial boilers is relatively low, the nominal pressure of the safety valve only needs to be higher than and as close as possible to the working pressure.

2.Determine the working pressure level of the safety valve according to the working pressure of the boiler

The set pressure of the safety valve can be adjusted by changing the spring preload compression, but each spring can only work normally within a certain set pressure range, and if it exceeds this range, another spring must be replaced. The valve is divided into different working pressure levels according to the set pressure range designed by the spring. Some people confuse the nominal pressure of the safety valve with the working pressure level, and think that the nominal pressure of the safety valve is 1.6MPa, and any pressure between 0 and 1.6MPa can be set. This view is wrong. Therefore, the working pressure range of the selected safety valve must include the working pressure of the boiler.

3.Determine the nominal diameter of the safety valve according to the boiler capacity

The rated discharge of the selected safety valve should be greater than and as close as possible to the rated evaporation of the boiler. The rated discharge of the safety valve is determined by the nominal diameter of the safety valve. The discharge volume and flow channel area are calculated according to the provisions of the "Steam Boiler Safety Technology Training Supervision Regulations" (hereinafter referred to as "Steam Regulations" and "Hot Water Boiler Safety Technology Supervision Regulations" (hereinafter referred to as "Hot Water Regulations").

Calculate the flow channel diameter d according to the flow channel area and determine the nominal diameter DN of the safety valve according to the standard. The "Steam Regulations" stipulates that the flow diameter of the safety valve should not be less than 25mm; the "Hot Water Regulations" stipulates that the flow diameter of the safety valve should not be less than 20mm.

4.Determine the number of safety valves according to the boiler capacity

The "Steam Regulations" stipulates that each boiler should be equipped with at least two safety valves, and boilers with rated evaporation less than or equal to that or only one safety valve. The "Hot Water Boiler" stipulates that for boilers with a rated thermal power greater than 1, at least two safety valves should be installed. Boilers with rated heating power less than or equal to at least one safety valve shall be installed.

All in all, only the correct selection of safety valves for industrial boilers can ensure the safe operation of boilers, meet the needs of production and life, and ensure the safety of national property and people's lives.

If you have any questions about boiler selection, please contact EPCB.

 EPCB, your private boiler system expert!

Further Reading:

Research on Energy Saving and Emission Reduction Strategy of Industrial Steam Boiler

How to Make Industrial Boilers Move Towards a New Stage of Automation and Intelligence?

Boiler Guidance| Industrial Boiler Operation Optimization and Adjustment Method