Common faults and precautions for sanitary diaphragm valves

(1) Leakage of the sealing surface of the bonnet. The valve head of the diaphragm valve is composed of bolts fastening the upper and lower valve covers and diaphragms, and the critical blocking oil of the main engine lubricating oil system is introduced into the chamber between the upper valve cover and the diaphragm. 

 

(2) The oil pressure disappears due to the rupture of the diaphragm, and the diaphragm valve is opened. The diaphragm valve diaphragm rupture, and the lubricating oil flows to the hot pipeline, so the machine has to be shut down and replaced with a new diaphragm. Subsequent inspection revealed a 3 mm diameter perforation at the point where the diaphragm came into contact with the spring tray.

 

 

 

(1) The adjustment door (for pressure relief) to adjust the oil pressure is a needle valve, which will gradually close during operation due to the influence of vibration and other factors, resulting in a slow rise in oil pressure, if the adjustment is not timely, the diaphragm will run under 0.80~0.85 MPa overpressure, which accelerates the damage of the diaphragm. In addition, when the main engine was doing the overspeed test, the speed rose to about 3 300 r/min, and the oil pressure of the diaphragm valve was once increased to 0.9 MPa due to the untimely adjustment, resulting in short-term overpressure.

 

(2) The design width of the sealing surface of the upper and lower bonnet is small. The inspection found that the sealing width of the leaking diaphragm (the part that was extruded and deformed) was less than 5 mm as a whole.

 

(3) The thickness of the upper and lower bonnet plates is only 5 mm, and the pressure is about 36 170 N calculated according to the diameter of the upper bonnet is 240 mm and the oil pressure is 0.8 MPa.

 

(4) The diaphragm installation process is unreasonable. The maintenance personnel are not familiar with the structural principle of the diaphragm valve, and when installing the new diaphragm, they do not take the measure of loosening the adjustment nut to make the spring lose the force, but carry out the diaphragm valve open. Due to the high position of the spring tray, the diaphragm is in contact with the upper bonnet, but there is a gap of 20 mm from the lower bonnet. In order to tighten the three together, it is necessary to forcibly connect with a long rod bolt (the purpose is to overcome the elastic force of the spring), and the bolt hole of the diaphragm is pulled and deformed, which is easy to cause damage, and the position of the bolt hole is offset inward and becomes elliptical relative to the bolt hole of the bonnet, the sealing surface becomes narrow, and the sealing effect becomes worse.

 

(5) There are bubbles in the colloidal part of the diaphragm, and there is delamination inside, and the maintenance personnel do not check carefully before replacement, and fail to find it in time, leaving hidden dangers after installation.

 

(6) Accidental damage to the diaphragm. The diaphragm is not properly protected during storage and installation, and the diaphragm is in contact with corrosive liquids or collides or extrudes with sharp parts of tools and parts (such as the protruding corners of the spring tray), damages or scratches the surface of the diaphragm, and fails to deal with it in time, resulting in potential leakage.

Aseptic sanitary diaphragm valves

 

(1) Carefully inspect the goods to prevent the use of substandard products. The diaphragm should be properly kept and stored; During the installation process, it is necessary to pay attention not to the diaphragm to be bumped or scratched; Pay attention to check the upper valve cover and spring tray, clean the burrs, and keep the contact parts smooth. After the above treatment, the diaphragm valve works well, ensuring the long-term normal operation of the main equipment.

 

(2) Prevent diaphragm overpressure operation. The operator should strengthen the monitoring, and if the oil pressure exceeds the standard, the maintenance personnel should be notified immediately to calibrate the pressure gauge. After confirming that the oil pressure has risen, the adjustment door should be slowly screwed to stabilize the pressure within the rated range. Special attention should be paid to the unit speed increase and the main engine overspeed test, send a special person to be responsible for monitoring the oil pressure on the spot and adjusting it in time.

 

(3) Transform the upper and lower valve covers. After demonstration and experiments, under the condition of keeping the safety oil pressure of the control oil system unchanged and not affecting the characteristics of the diaphragm valve, the newly processed bonnet imitates the design form of the original parts, increases the thickness to 10 mm, and increases the width of the sealing surface to 10 mm. This measure was implemented in 2003 and 2004 on the No. 1 and No. 2 aircraft, and the results have been good, and there has been no leakage so far.

 

(4) Improve the diaphragm installation process. Before replacing the diaphragm, first measure and record the exposed size of the adjustment nut, and screw it down so that the spring is free and the spring tray is in a low position. At this moment, the diaphragm is installed, there is no longer a gap, and the bolts can be tightened symmetrically and evenly. After installation, screw the adjustment nut upwards to its original position.