In order to ensure the safety of the boiler, the boiler is equipped with safety valves which are widely used in various pressure vessels and piping systems. This is a very important protection valve. However, there are some common failures in the safety valve, such as the low back pressure of the safety valve. Low back pressure relief valve on the economic operation of the boiler has a great hazard, back seat pressure is too low will cause a large number of medium-time emissions, resulting in unnecessary energy loss. This failure occurred in the A49H-type spring pulse relief valve used by the 200MW unit, then why the back pressure of the safety valve of the boiler is low? 1. Spool and guide sleeve with improper clearance, with the gap is small, in the impulse safety valve Kai seat, instant throttle in this area to form a higher kinetic energy pressure zone, the valve core elevation, delayed back seat time When the container is lowered to a lower level, the pressure in the kinetic energy pressure zone is reduced and the impulse valve returns to seat. Way to eliminate this failure is to carefully check the size of each part of the valve plug and the guide sleeve, with the gap is too small, reducing the diameter of the valve disc sealing surface straight valve cap or increase the radial clearance between the valve disc and the guide sleeve , To increase the flow area of ​​the site, so that steam will not flow too much over the throttling, leaving the local pressure rise to form a high kinetic energy pressure zone. 2. The friction of various sports parts, some parts have jam. The solution is to carefully check the various sports parts, maintenance standards in strict accordance with the maintenance of the various components, the parts with the gap adjusted to the standard range, eliminating the possibility of jam. 3. Spring pulse relief valve on the steam discharge, this form of impulse safety valve is opened, the media continue to discharge, promote the main safety valve action. On the one hand, the pressure before the relief valve due to the main relief valve medium displacement is not enough and continue to rise, so the pulse tube steam along the steam drum or gas header continue to flow to the impulse safety valve to maintain impulse safety valve action. On the other hand, due to this type of impulse safety valve medium flow through the gap between the valve core and the guide sleeve flows to the main safety valve piston chamber, medium out of the sealing surface of the impulse safety valve to form a dynamic pressure zone around it, The valve lift, so to achieve the momentum of the relief valve to continue emissions, the greater the steam emissions, the spool part of the kinetic energy pressure zone greater pressure on the role of the upward thrust on the valve, the greater the impulse safety valve Easy to back seat. The way to eliminate this kind of failure is to close the throttle valve so that the flow rate of the medium flowing out of the relief valve is reduced and the pressure in the dynamic pressure area is reduced so that the impulse safety valve can be returned to the seat.