Abnormal Opening & Closing and Leakages of Safety Valves

Abnormal Opening & Closing and Leakages of Safety Valves


Opening and closing over set pressure means that the equipment is opened or closed over its set pressure. In this case, the overload protection function of the safety valve loses, and the reasons and countermeasures are as follows:
(1) The set pressure is inaccurate, and it is too high. Countermeasures: readjust the compression of the spring.
(2) The valve disc is stuck to the valve seat, because the safety valve is not used during long-term operation, and has not been regularly inspected and maintained, causing rust, resulting in the valve disc sticking to the valve seat. Countermeasures: regularly conduct manual air or water discharge tests on the safety valve, and pay attention to moisture during use.
(3) The internal part is blocked by the foreign matter, and the valve clack cannot rise by overcoming the obstacle, resulting in an increase in the opening pressure or failing to open. Countermeasures: Check and remove foreign bodies.
(4) The external part is blocked by foreign objects, and the external artificial weight of the dead-weight, lever-type safety valve or other reasons hinder the normal opening of the valve disc. Countermeasures: Check and remove foreign bodies.
(5) The working temperature decreases, resulting in an increase in the opening pressure. Countermeasures: value at normal temperatures should be slightly lower than the required opening pressure value when adjusted at normal temperatures and used at low temperatures. The valve is opened lower than the set pressure.
 
The set pressure is not allowed. Countermeasures: re-adjust the compression of the spring. The spring ages and elasticity decreases. The spring will age due to long-term use or corrosion of the medium, and the elasticity will decrease. Countermeasures: properly tighten the adjusting screw or replace the spring. The working temperature increases, resulting in a decrease in the opening pressure. Countermeasures: the set pressure value at normal temperatures should be slightly higher than the required opening pressure value. Leakages and other reasons make the operating environment of the safety valve higher than the allowable working temperature of the spring, causing the spring force to drop. Countermeasures: Grind the sealing surface in time to eliminate leakages and replace the new spring. The safety valve is inclined due to installation or pressing. Countermeasures: Safety valves, especially static-weight safety valves and lever-type safety valves must be installed vertically with a solid protective ring.
 
Leakages of safety valves
Under the normal working pressure of the equipment, the leakage between the valve disc and the sealing surface of the valve seat exceeds the allowable amount of leakages.
(1) There are impurities between the valve disc and the sealing surface of the valve seat. Countermeasures: Use a lifting wrench to open the valve several times to wash away impurities or dirt. 
(2) There is damage to the sealing surface. The deformation or dislocation of the sealing surface caused by the safety valve popping and returning to the valve seat due to the material, hardness, assembly and other reasons of the sealing surface, or the expansion and deformation of the sealing surface caused by the temperature change of the sealing medium may lead to leakages of media. Countermeasures: Choose a safety valve made of suitable materials according to the nature of the sealing medium and possible temperature changes. For defects or damages to the sealing surface of the safety valve, grinding or turning after grinding should be used to repair the defects or damages depending on the situation. At the same time, pay attention to grinding to prevent grooves.
(3) The gasket is damaged. The gasket is damaged due to blocking, squeezing and pressing of impurities or hard objects. Replace the qualified gasket, and pay attention to cleaning the installation position and installation objects first when placing the gasket. 
(4)The valve stem is bent and inclined, making the valve disc and valve seat dislocation. Countermeasures: Reassemble or replace the valve stem.
(5) The elasticity of the spring is reduced or lost, because the spring is corroded by the medium or the temperature of the medium increases, making the spring soft, the preload reduce, and leakages occur. Countermeasures: Strengthen the anti-corrosion and heat insulation measures of the spring; replace the spring in time or re-adjust the opening pressure.
(6) The spring is broken. Countermeasures: replace the spring.
(7) The assembly is improper or size of relevant parts is inappropriate. The valve core and valve seat are not completely aligned or there is light transmission for the joint surface in the assembly process. The reason is that the sealing surface of the valve core and valve seat is too wide, which is not conducive to sealing. Countermeasures: Check the size and uniformity of the matching gap around the valve core to ensure that the top hole of the valve core and the sealing surface are in the same positive degree; check the clearance of each part and do not allow the valve core to be lifted; the drawings require that the width of the sealing surface should be appropriately reduced to achieve effective sealing.
(8)The joint surface of the valve body leaks, and the bolts on the joint surface are not fastened enough or are too tight, resulting in poor sealing of the joint surface; the sealing gasket of the joint surface of the valve body does not meet the standard. Countermeasures: Adjust the bolt tightening force. When tightening the bolt, it must be tightened diagonally. It is best to measure the gaps around the corner while tightening; tighten the bolts until they can no longer be tightened, and make the gaps on the joint surface consistent. Also, a gasket meeting the standard should be used.
(9) The contact between the valve stem and the valve disc is corroded, resulting in  the valve disc not being able to be in the position. When the exposed valve stem is moved, the valve disc is displaced with it, resulting in a failure of the sealing and leakages. Countermeasures: Regularly check the contact groove between the valve stem and the valve disc, and take reasonable anti-rust measures.
(10) The set pressure is too close to the working pressure of the equipment, because the fluctuation range of the working pressure of the equipment is close to or exceeds the sealing pressure of the safety valve, which may cause leakages. Countermeasures: choose an appropriate safety valve, and reasonably set the set pressure of the safety valve.