The double spring safety valve relies on the force of the spring to press the spool on the valve seat, so that the safety valve is in a closed state, and the bottom of the spool is subjected to the upward force of steam.
In normal operation, the downward compression force of the spring is greater than the upward thrust of the steam, and the valve is in a closed state.When the steam pressure reaches the seat pressure of the safety valve, the force of the steam on the spool is greater than that of the spring, which makes the spool rise and the safety valve exhaust steam.
The starting pressure of the safety valve can be adjusted by changing the tightness of the spring through the adjusting screw on the upper part of the valve stem.
The double spring safety valve has the advantages of convenient adjustment, small volume and weight, large exhaust capacity and so on. It is suitable for boilers with different parameters and different capacities.
1. The action point of the valve stem force is reduced and the sealing performance is improved.
The acting point of the stem force of the ordinary flat disc is not only higher than the sealing surface, but also not directly acting on the disc.
For the valve with flexible disc, the force acting point of the stem is reduced below the sealing surface and acts directly on the disc.
This structural improvement greatly improves the anti-vibration ability of the valve, that is, the sealing stability is greatly improved.
In other words, when the valve has the same degree of vibration, the flexible disc valve is less prone to leakage.
This performance has been verified in the actual operation of the safety valve.
2. The 'flexible disc' structure not only improves the operating sealing performance, but also increases the operating pressure value to maintain the tightness.
For the design of a flat disc, the valve will 'pre-release' when the operating pressure rises to the set pressure of the valve.
For the double spring safety valve, the existence of 'pre-leakage' is a normal phenomenon, and the existence of 'pre-leakage' can help the double spring safety valve take off to a certain extent.
Therefore, the difference between the design pressure and the larger operating pressure of the double spring safety valve is set at more than 5%.
The 'flexible disc' structure introduces the system pressure into the annular groove on the back of the disc sealing surface and acts on the annular inclined surface opposite to the disc sealing surface. Because the sealing surface has a certain elasticity, with the increase of the medium pressure in the system, the disc sealing surface is pushed down by the system pressure to produce a small deformation, which is closely combined with the nozzle sealing surface, thus delaying the valve pre-discharge point.
On the premise of ensuring the accurate setting pressure of the valve, the 'flexible disc' structure can make the valve leak-free when the operating pressure reaches more than 96% of the set pressure.
The statistics of the setting and verification results of the double spring safety valve show that the pre-discharge point of the coal machine accessory safety valve of the flexible disc can reach 98.5% or even 99% of the setting pressure, and the take-off is accurate, the return seat is simple, and there is no leakage.
