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Spring type safety valve description and maintenance series

Dec 24, 2018

Spring type safety valve manual

Second, installation, use and adjustment
1. installation
The pipeline must be thoroughly cleaned and purged before the safety valve is installed.
The safety valve must be installed vertically, the inner diameter of the inlet pipe is not less than the inlet diameter of the safety valve, and the necessary support is required.

The inner diameter of the outlet discharge pipe should not be less than the outlet diameter of the safety valve. The discharge resistance should be as small as possible. The general resistance pressure drop is less than 10% of the set pressure.
The drain pipe shall be installed at the lowest position of the discharge pipe and shall be separate and shall not be connected in series with other drain pipes.
When the valve is equipped with a hydraulic compression screw, when the valve participates in the hydraulic test of the container or piping system, the screw can be screwed onto the bonnet as shown in the figure to resist the valve stem and prevent the valve from opening. After the hydrostatic test is completed, the screw should be unscrewed from the bonnet. If possible, it is best not to involve the valve in the hydraulic test of the vessel or piping system.
Special attention must be paid to the connection of the inlet end of the valve during field installation. A sealing gasket (flexible graphite composite mat) is attached to the safety valve at the inlet end, or the inner and outer circles of the gasket at the inlet of the self-contained inlet should be in accordance with the requirements of Figure 8 and must be sealed. The end face of the inlet flange of the safety valve is placed centrally, and the purpose is to block a matching gap of the valve base. In the installation of the mating flange, special attention should be paid to the fact that the gasket cannot be off center, otherwise the medium will bypass the gasket and leak through the gap to the outlet of the valve.
The leak, which is often mistaken for leakage on the sealing surface of the safety valve.
The same high neck and convex flanges are matched with each other (see Figure 9), which is accompanied by a sealing gasket (flexible graphite composite mat) with the safety valve, or the inner and outer circles of the self-assembled gasket should be sealed. The purpose of Figure 9 is to block a matching gap of the valve base.
 2. use
The correct valve type and specification should be selected based on parameters such as pressure, temperature, media and displacement. When the medium temperature is above 350, a safety valve with a heat insulation frame structure should be used.
3. Adjustment
The adjustment of the valve's take-off (tuning) pressure can be adjusted by using the adjusting nut in the bonnet to rotate smoothly and counterclockwise (see Figure 10). Rotating clockwise increases the take-off pressure and vice versa. When adjusting the take-off (setting) pressure, the pressure at the inlet end of the safety valve must be reduced. The reduced value is generally less than 50% of the take-off (set) pressure and requires qualified personnel to be trained.
The adjustment of the discharge and return pressure (performance index) can be adjusted by using the adjustment ring in the body cavity by slewing and counterclockwise rotation. The specific adjustment method is as follows:
a) first reduce the valve inlet pressure;
b) Remove the set screws in the nut and nut. When using the single adjustment ring structure of the medium and low pressure products, use a screwdriver or other tool to rotate the adjustment ring clockwise (the ring moves down) to increase the return pressure and discharge pressure. Help the valve to return to the seat in time. Conversely, reducing the return pressure and discharge pressure is also not conducive to returning to the seat. When using the double adjustment ring structure of the secondary high pressure product), the counterclockwise rotation of the upper ring (upward movement of the ring) can increase the discharge pressure and the return pressure, which is beneficial to the return of the valve. Conversely, the discharge pressure and the return pressure are reduced. Rotating the lower ring clockwise (turning down the ring) increases the return pressure and discharge pressure, and also helps the valve to return to the seat in time. Conversely, the return pressure and discharge pressure are reduced;

To replace the set screw of the fixed adjusting ring, the head of the screw must be inserted into the tooth groove of the adjusting ring and locked with a nut, but a radial force cannot be generated to the adjusting ring;
c) After the adjustment is completed, the inlet end of the valve can be gradually boosted, and the valve will start to jump and start to judge whether it needs further adjustment according to the result of the operation.

Third, daily maintenance
1. Always check the sealing performance of the safety valve and the tightness at the connection to the pipe;
2. When the safety valve has a take-off action during operation, check for abnormal conditions and record;
3. If the safety valve is found to be abnormal (leakage or other malfunction), it should be repaired or replaced in time;
4. In the operation of the boiler, the safety valve should be periodically discharged and the boiler should be stopped.
When re-enabled, the safety valve also requires a manual discharge test.
Common faults and troubleshooting methods
1. Valve Leakage: Leakage above the allowable value occurs between the disc and the seat sealing surface under normal operating pressure of the equipment.
There is dirt on the sealing surface. The valve can be opened several times with a lifting wrench to flush the dirt;
a) Damage to the sealing surface. It can be repaired by grinding or turning and grinding, and the flatness and roughness of the sealing surface are ensured after repair;
b) The coaxiality of the valve parts is damaged due to factors such as improper assembly or pipe load. The additional load of the pipe should be reassembled or excluded;
c) The valve setting pressure is too close to the normal working pressure of the equipment. The opening pressure should be appropriately adjusted according to the equipment strength conditions;
d) The spring is loosened due to corrosion of the high temperature medium and the opening pressure is lowered and the valve is leaked. The spring should be replaced according to the reason.
2. The safety valve is not flexible: it means that the action is not flexible when opening and returning, or not returning after opening.
The position of the adjusting ring is improper, causing the valve opening process to be prolonged or the seat returning is slow, and should be adjusted again;
a) Internal moving parts have defects such as bumps or burrs, and parts should be replaced.
3. Setting pressure value change: The allowable deviation value is in accordance with the provisions of GB/T12243-2005 standard.
The change of working temperature, because the valve is adjusted at normal temperature, can be adjusted by adjusting the screw sleeve, if it is improperly selected, the model should be replaced;
a) Spring corrosion, when the medium is highly corrosive, the spring should be replaced, or a safety valve of other structure should be selected;
b) When the influence of back pressure is large, the back pressure balanced safety valve should be used;
c) The internal moving parts of the valve are jammed and should be checked and removed.
4. Valve frequency jump
Inappropriate valve diameter selection;
a) the inlet pipe diameter is too small or the resistance is too large;
b) the discharge pipe resistance is too large;
c) the spring stiffness is too large;
d) Improper position of the adjustment ring makes the return pressure too high.
Fourth, regular inspection
1. Whether the safety valve is installed correctly;
2. Whether the information of the safety valve is complete (nameplate, quality certificate, installation number, verification record and report);
3. Whether the seal of the external adjustment mechanism of the safety valve is intact;
4. Whether there are factors affecting the normal function of the safety valve;
5. When the shut-off valve must be installed, the seal of the shut-off valve before and after the inlet of the safety valve is intact and in the normal open position;
6. Safety valve with or without leakage;
7. Whether there is corrosion on the exterior of the safety valve;
8. The venting holes provided for the bellows should be open and clean;
9. The lifting device (wrench) is active and in place;
10. The external accessories of the safety valve are intact and normal.

V. Standard Specifications for Implementation
1. The design and manufacture of the valve is in accordance with the provisions of GB/T 12243 "Spring Direct Load Safety Valve";
2. The valve seal leakage rate is assessed in accordance with the API 527 "Valve Sealing Degree of Pressure Relief Valves" standard;
3. The valve specifications and selections are in accordance with the provisions of GB/T 12241 "General requirements for safety valves";
4. The valve connection is in accordance with GB/T 9113 "Steel Pipe Flange" or JB/T 79.1 and JB/T 79.2 "Integral Steel Pipe Flange" and GB/T 12224 "General Requirements for Steel Valves".