In industrial production, safety valves are essential devices for ensuring the safe operation of equipment. They can automatically open when the internal pressure of equipment exceeds the set value, releasing excess pressure and preventing the equipment from experiencing danger due to overpressure. However, to ensure that the safety valve can accurately operate at the set pressure, adjustments before leaving the factory and before installation are critical. This article provides a detailed introduction to the methods and precautions for adjusting safety valves, helping users correctly set them and ensuring the safe operation of equipment.
Before leaving the factory, manufacturers adjust the opening pressure of each safety valve to reach the set value required by the user. If the user specifies a spring working pressure level, manufacturers generally adjust it according to the lower limit of that level. This adjustment ensures that the safety valve already possesses a basic set pressure at the time of leaving the factory, but it should be noted that this does not mean the safety valve does not require further adjustment when installed on specific equipment.
Before installing the safety valve on the protected equipment, users must re-adjust the safety valve on site. This is because the actual operating conditions of the equipment may differ from the testing conditions at the factory, including factors such as medium type, temperature, and back pressure. The purpose of re-adjustment is to ensure that the set pressure fully meets the actual operating requirements so that the valve can accurately open at the set pressure during equipment operation.
Clean the valve: Before adjustment, the interior of the safety valve should be thoroughly cleaned to ensure no impurities or dirt remain. At the same time, a clean medium should be used for testing to prevent impurities from adversely affecting the adjustment process or valve performance.
Reduce inlet pressure: Before performing any adjustments, the inlet pressure of the safety valve must be reduced to below 90% of the opening pressure. This step is crucial because if the inlet pressure is too high, the valve disc may rotate during adjustment, damaging the sealing surface and affecting the valve's sealing performance.
Rotate the adjusting screw: Within the spring working pressure range indicated on the nameplate, rotate the adjusting screw to change the compression of the spring, thereby adjusting the opening pressure. During adjustment, slowly increase the valve inlet pressure until the valve lifts once and observe whether the opening pressure meets the requirement.
If the opening pressure is too low, tighten the adjusting screw clockwise.
If the opening pressure is too high, loosen the adjusting screw counterclockwise.
After reaching the desired opening pressure, tighten the lock nut and reinstall the valve cap.
Matching medium conditions: To ensure the accuracy of the opening pressure, the medium used during adjustment should be as close as possible to the actual operating conditions. If the actual operating medium differs from the adjustment medium, especially when the accumulation state of the medium differs (for example, changing from liquid to gas phase), the opening pressure may change. Additionally, an increase in working temperature usually leads to a decrease in opening pressure. Therefore, if adjusted at room temperature for high-temperature use, the set pressure at room temperature should be slightly higher than the required opening pressure. The exact extent should be selected based on the valve's structure and material, following the manufacturer's instructions.
For conventional safety valves used in applications with fixed additional back pressure, when adjusting the opening pressure after inspection, the set value should be the required opening pressure minus the additional back pressure. This is because back pressure affects the actual opening pressure of the valve and must be considered during adjustment.
Adjusting the discharge pressure and reseating pressure requires a full-lift test of the valve. Therefore, such adjustments are generally only possible on large-capacity test devices or after the safety valve has been installed on the protected equipment. Different safety valve structures have different adjustment methods.
For this type of safety valve, adjustment is performed using the seat adjusting ring. After loosening the fixing screw of the adjusting ring, a thin iron rod or similar tool can be inserted into the exposed screw hole to move the teeth of the adjusting ring, allowing the ring to rotate left or right.
When the ring is rotated counterclockwise (left), its position rises, lowering both the discharge pressure and the reseating pressure.
Conversely, when rotated clockwise (right), its position lowers, increasing both pressures.
During each adjustment, the rotation of the adjusting ring should not be too large; generally, rotating a few teeth is sufficient. After adjustment, tighten the fixing screw so that its end is located in the groove between two teeth of the ring, preventing rotation without applying radial pressure. Before moving the adjusting ring, the inlet pressure of the safety valve should be appropriately reduced, generally below 90% of the opening pressure, to prevent the valve from opening suddenly during adjustment and causing an accident.
This type of safety valve is more complex to adjust.
The seat (lower) adjusting ring changes the size of the passage between the disc and the ring, affecting the degree of pressure accumulation in the chamber between the disc and the ring during initial valve opening. Raising the seat adjusting ring increases pressure accumulation, reducing the proportional opening phase and causing the valve to reach rapid full lift more quickly. Therefore, raising the seat adjusting ring can lower the discharge pressure. However, it must not be raised too close to the disc, as this may cause premature sudden opening or frequent popping. The seat adjusting ring mainly reduces the proportional opening phase and adjusts discharge pressure, while also affecting the reseating pressure.
The upper adjusting ring changes the deflection angle of the medium flowing under the disc, altering the fluid force and thereby adjusting the reseating pressure. Raising the upper ring decreases the deflection angle, reducing fluid force and increasing reseating pressure; lowering it does the opposite. While the upper ring affects discharge pressure, its impact is less significant than on reseating pressure.
Adjustment steps: Open the lower lead seal, loosen the adjusting ring's locking screw, and use a thin iron rod or similar tool through the screw hole to rotate the ring teeth. If the safety valve outlet has no connecting pipe, the adjustment rod can be inserted directly from the outlet. For safety, the inlet pressure should be reduced to below 80% of the opening pressure before adjustment to prevent sudden valve opening. Each adjustment should rotate the ring only 2–5 teeth. After adjustment, tighten the locking screw, ensuring its end sits in the groove between two teeth to prevent loosening. For valves with both upper and lower adjusting rings, adjust the lower ring first to achieve the preset discharge pressure, then adjust the upper ring for reseating pressure. During testing, mutual interference may occur and repeated adjustments may be necessary until satisfactory.
Selection of medium parameters: Where conditions permit, use medium parameters as close as possible to actual operating conditions to ensure accurate opening pressure. If this is not possible, gas or steam safety valves can use air for set pressure adjustment, and liquid or water safety valves can use room-temperature water. When the actual medium temperature differs significantly from the adjustment medium, temperature compensation should be considered.
Pressure gauge calibration: Pressure gauges used for set pressure adjustment should be regularly calibrated, with accuracy of Grade 1 or higher. The set pressure should be within one-third to two-thirds of the gauge range, with a dial diameter ≥100 mm. Using accurate gauges ensures adjustment accuracy.
Avoid abnormal actions: During testing, avoid abnormal actions such as chattering or fluttering, which may damage the sealing surface and affect valve performance and lifespan. If such phenomena occur, stop immediately, check the cause, and take corrective action.
Position of adjusting rings: After adjustment, the relative positions of the upper and lower rings should not be too close, as this may affect the valve's discharge capacity. Generally, the annular area between the rings should not be smaller than the throat area of the valve seat.
Proper adjustment of safety valves is crucial to ensuring the safe operation of industrial equipment. As described in this article, safety valves require precise adjustments both before leaving the factory and before installation. During adjustment, attention should be paid to matching medium conditions, pressure gauge accuracy, the position of adjusting rings, and avoiding abnormal actions. Only by strictly following correct steps and methods can safety valves reliably open at the set pressure in actual operation, effectively protecting equipment and personnel. This article aims to provide valuable reference and guidance for safety valve users.
