In industrial production, safety valves are important devices that ensure the safe operation of equipment. They can automatically open when the equipment pressure exceeds the set value, releasing excess pressure and thereby protecting the equipment from damage. However, to ensure that the safety valve can function properly at critical moments, correct adjustment is essential. This article will provide a detailed introduction to the adjustment methods and precautions for safety valves, helping users better understand and operate them.
Before leaving the factory, each safety valve is adjusted by the manufacturer so that its opening pressure reaches the set value required by the user. If the user specifies the working pressure grade of the spring, the adjustment is usually made to the lower limit of that pressure grade. However, this does not mean that users can rely entirely on the factory settings. Before installing the safety valve onto the protected equipment, it must be readjusted on site to ensure that its set pressure value meets actual requirements.
Adjusting the opening pressure of a safety valve is mainly done by rotating the adjustment screw to change the compression of the spring. Before adjustment, the inlet pressure of the valve needs to be reduced to below 90% of the opening pressure, so as to prevent the valve disc from being driven to rotate while turning the adjustment screw, which would otherwise damage the sealing surface. In addition, to ensure the accuracy of the opening pressure value, the medium conditions during adjustment, such as type of medium and temperature, should be as close as possible to the actual operating conditions. This is because changes in medium type and temperature may affect the opening pressure of the safety valve.
Changes in medium type, especially when the aggregate state of the medium changes (for example, from liquid phase to gas phase), usually cause changes in opening pressure. For example, in safety valves used for gas or steam, temperature variations of the medium in actual use may affect the opening pressure. When the working temperature increases, the opening pressure generally decreases. Therefore, if the safety valve is adjusted at normal temperature, but in actual use it is under high-temperature conditions, the set pressure value at normal temperature should be slightly higher than the required opening pressure. The specific margin depends on the structure and material of the valve and should generally refer to the manufacturer’s instructions.
The adjustment methods vary depending on the structure of the safety valve. Understanding these differences and mastering the correct adjustment methods are key to ensuring the proper functioning of the safety valve. Below are detailed introductions of several common safety valve structures and their adjustment methods.
For safety valves equipped with a blowdown disk and a seat adjusting ring, the method of adjusting the discharge pressure and reseating pressure is to use the seat adjusting ring. The specific steps are as follows:
Loosen the fixing screw of the adjusting ring: First, loosen the fixing screw of the adjusting ring so that the ring can be turned.
Move the adjusting ring: Use a thin iron rod or similar tool, insert it through the exposed screw hole, and move the gear teeth of the adjusting ring to rotate the ring left or right. If you need to lower the discharge pressure and reseating pressure, turn the adjusting ring to the left counterclockwise; if you need to increase them, turn the ring to the right clockwise.
Control the adjustment range: Each adjustment should not involve too much rotation; generally, just a few teeth are enough. After adjustment, tighten the fixing screw so that its end is located in the groove between two teeth of the adjusting ring. This prevents the ring from turning but does not apply radial pressure on it.
Lower the inlet pressure: Before moving the adjusting ring, the inlet pressure of the safety valve should be reduced appropriately (generally below 90% of the opening pressure) to prevent accidental opening of the valve during adjustment, which may cause accidents.
For safety valves with upper and lower adjusting rings, the adjustment process is more complex. The steps are as follows:
Adjust the lower adjusting ring: First, adjust the lower adjusting ring by changing the size of the passage between the valve disc and the adjusting ring, thereby changing the degree of pressure accumulation in the chamber between them during the initial opening of the valve. Raising the seat adjusting ring increases pressure accumulation, reduces the proportional opening phase, makes the valve open rapidly, and lowers the discharge pressure. However, the seat adjusting ring should not be raised too close to the valve disc, otherwise premature rapid opening and chattering may occur.
Adjust the upper adjusting ring: The upper adjusting ring changes the angle at which the flowing medium is reflected and deflected beneath the valve disc, thereby changing the fluid force and adjusting the reseating pressure. Raising the upper adjusting ring reduces the deflection angle, decreases fluid force, and increases reseating pressure; lowering it decreases the reseating pressure. The upper adjusting ring also affects discharge pressure, but its impact is less significant than on reseating pressure.
During adjustment, note that the relative positions of the upper and lower adjusting rings must not be too close, otherwise the valve discharge capacity will be affected. Generally, the annular area between the two rings should not be smaller than the throat area of the valve seat. In addition, abnormal actions such as chattering or vibration must be avoided during adjustment to prevent damage to the sealing surface.
After the safety valve is adjusted, it should be sealed with lead to prevent random changes to the adjusted state. When repairing the safety valve, the positions of the adjustment screw and adjusting rings should be recorded before disassembly to facilitate re-adjustment after repair. After readjustment, the valve should again be sealed.
Adjustment Steps for Opening Pressure
Open the seal and remove components: Open the top seal, remove the lifting lever, remove the valve cap, and loosen the locknut.
Adjust the spring preload compression: Within the specified working pressure range of the spring, rotate the adjusting screw sleeve to change the spring’s preload compression to adjust the opening pressure.
Perform a test: During adjustment, gradually increase the valve inlet pressure until the valve pops open once. If the opening pressure is too low, release the inlet pressure and tighten the adjusting screw sleeve clockwise; if the opening pressure is too high, loosen the screw sleeve counterclockwise.
Lock and install: After the opening pressure has been adjusted to the required value, tighten the locknut and reinstall the valve cap.
Replace the spring: If the required opening pressure exceeds the spring’s specified working pressure range, replace the spring with another one of the appropriate pressure grade and then readjust. After replacing the spring, the corresponding data on the nameplate should be updated.
Clean and use clean medium: Before adjustment, the inner chamber of the valve should be cleaned, and clean medium should be used for testing.
Avoid rotation of the valve disc: When the inlet pressure approaches the opening pressure (i.e., exceeds 80% of the opening pressure), the adjusting screw sleeve must not be rotated to avoid rotating the valve disc and damaging the sealing surface.
Approach actual working conditions: If possible, adjust using medium parameters close to actual working conditions to ensure accuracy of the opening pressure value.
Medium temperature differences: If the same medium as in actual operation cannot be used, gas or steam safety valves can be adjusted with air, and liquid or water safety valves can be adjusted with room-temperature water. If the actual medium temperature differs greatly from the test temperature, temperature compensation should be considered.
Pressure gauge calibration: The pressure gauge used for adjustment should be calibrated regularly, with accuracy no lower than Grade 1. The set pressure should fall within one-third to two-thirds of the gauge’s range, and the dial diameter should be at least 100 mm.
If the opening pressure has been adjusted but the discharge or reseating pressure does not meet requirements, the position of the adjusting ring can be changed. The steps are:
Open seal and loosen screws: Open the lower seal and loosen the adjusting ring set screw.
Move the adjusting ring: Use a thin iron rod inserted through the screw hole to move the gear of the adjusting ring. If the safety valve outlet has no connected pipe, the rod can be inserted directly from the outlet.
Lower the inlet pressure: For safety, reduce the inlet pressure appropriately before adjustment (generally below 80% of the opening pressure) to prevent sudden opening during adjustment.
Control adjustment range: Each rotation should not be excessive, generally 2–5 teeth. After adjustment, immediately tighten the set screw so that its end is in the groove between two teeth of the adjusting ring to prevent loosening.
Repeated adjustment: For safety valves with both upper and lower adjusting rings, normally adjust the lower ring first to achieve the desired discharge pressure, then adjust the upper ring. Interference may occur during testing, so repeated adjustments are necessary until satisfactory results are obtained.
The test bench used to adjust discharge and reseating pressure should have a sufficiently large air source flow to ensure that the valve can reach full opening (i.e., full lift of the safety valve) during testing. Otherwise, the measured discharge and reseating pressures will not be accurate.
The correct adjustment of safety valves is critical to ensuring the safe operation of industrial equipment. Through this detailed introduction, users should clearly understand the basic requirements for adjustment, the methods for different structures of safety valves, and the precautions during the process. In actual operation, it is essential to strictly follow these steps and requirements to ensure that the safety valve can work properly at critical times, protecting both equipment and personnel safety.
