Spring Safety Valve Series

A38Y-16C/25/4aA43H-16C/25/40A37H-16C/25/40  

The spring-loaded safety valve is suitable for equipment and pipelines handling steam water and other mediums with working temperatures of ≤350℃. As an overpressure protection device, the connecting flange standard is in accordance with the JB/T-94 series.

Working Principle:

Based on the analysis of the opening action characteristics of spring-loaded safety valves, it can be concluded that: under the influence of the external force FW, throughout the entire process of a safety valve transitioning from closed to open and then from open to closed, the variation规律 of the external additional force FW is such that when the additional force gradually increases from zero to match the sum of the internal pressure PL×S with the spring pre-tension force, the valve slightly opens, increasing the effective area S of the medium. This causes the internal pressure force required to overcome the spring pre-tension to急剧 increase, resulting in an instantaneous decrease in the external additional force. This leads to the appearance of the characteristic peak A. As the external additional force gradually diminishes and reaches the closing point, due to the sudden decrease in the effective area of the medium, to maintain the balance of forces, there is a momentary rebound in the external additional force, resulting in the second characteristic peak B. These two characteristic peaks A and B serve as the technical basis for detecting the opening pressure and the return seat pressure of safety valves under online conditions.

Structure:

Safety valves are categorized by their structural form into pendulum, lever, spring, and pilot (pulsating) types; and by the valve body construction, they can be either sealed or unsealed. Sealed safety valves ensure that the released medium does not escape externally, but is discharged entirely along the outlet to the designated location. They are generally used in environments with toxic or corrosive media. For safety valves used with air and steam, unsealed types are more commonly adopted. When selecting safety valve products, the actual sealing pressure should be determined. For spring-loaded safety valves, within a specified nominal pressure (PN) range, several working pressure grades of springs are available. When placing an order, in addition to specifying the model, name, medium, and temperature of the safety valve, the valve body sealing pressure should also be noted; otherwise, the supply will be made according to a default sealing pressure.

Installation and Maintenance:

All safety valves should be installed vertically.

The safety valve outlet should be free of resistance to prevent pressure build-up.

The safety valve should be tested specifically before installation and its sealing integrity should be checked.

Regular inspections should be conducted on safety valves in use.

The installation of the safety valve should comply with the following requirements:

(l) Boilers with a rated evaporation capacity greater than 0.5t/h must be equipped with at least two safety valves; for boilers with a rated evaporation capacity of 0.5t/h or less, at least one safety valve is required. Safety valves must be installed at the outlet of the dividing economizer and at the outlet of the steam superheater.

(2) The safety valve should be vertically mounted at a high position on the boiler and header. No outlet pipes or valves for steam extraction should be installed between the safety valve and the boiler drum or header.

(3) The lever-type safety valve must have a device to prevent the heavy hammer from moving freely and a guide frame to restrict the lever from derailing. The spring-type safety valve should have a lifting handle and a device to prevent the adjustment screw from being loosened arbitrarily.

(4) For boilers with a rated steam pressure of 3.82MPa or less, the safety valve throat diameter should not be less than 25mm; for boilers with a rated steam pressure greater than 3.82MPa, the safety valve throat diameter should not be less than 20mm.

(5) The connecting pipe between the safety valve and the boiler should have an area not less than the inlet area of the safety valve. If several safety valves are installed together on a short pipe that is directly connected to the drum, the passage area of the short pipe should not be less than 1.25 times the total steam discharge area of all the safety valves.

(6) Safety valves should generally be equipped with exhaust pipes, which should lead directly to a safe location and have an adequate cross-sectional area to ensure smooth exhaust flow. The bottom of the exhaust pipe of the safety valve should have a drain pipe connected to a safe location, and valves should not be installed on either the exhaust pipe or the drain pipe.