Technical Articles
Common Breakdowns of Valves (Part One)
Posted: 08/12/2017 15:17:57  Hits: 4
Valves are only small parts in factories. However, once there is a breakdown of them, it can cause a lot of trouble. Which part should we check when a breakdown of the valve happens?

1. Inner walls of valve bodies 
For regulating valves used in places with high pressure differences and corrosive media, we must seriously check pressure and corrosion resistance of regulating valves. Because inner walls of regulating valves' bodies are often subject to impacts and corrosion of the media. 

2. Valve seats
When regulating valves are working, surfaces of internal threads which are used for fixing the regulating valve seats are easily to be corroded due to permeation of the media, resulting in loose valve seats. Therefore, we need to pay attention to internal threads. We should also check whether sealing surfaces of valve seats are damaged or not, especially for valves operated under high pressure differences.


3. Valve spools
Valve spools are the flexible parts when regulating valves are working; valve spools are the most serious corroded parts due to scouring of the media; under the circumstance of high pressure differences, wear of valve spools is more serious; therefore, we need to carefully check every part of the valve spool to find out whether it is corroded or wear or not; When the valve spool is damaged, it should be replaced. Moreover, we also need to check whether or not the valve stem has the same problem as the valve spool or the connection between the valve stem and the valve spool is loose.

4. "O" seal rings and other gaskets
Check whether "O" seal rings and other gaskets are aging or cracked or not.

5. PTFE packing and sealing lubricating grease
Check whether PTFE packing is aging or not; check whether the contact surface is damaged or not and it should be replaced if necessary.

What can we do when outer leakages occur in regulating valves?
1. Using the sealing grease
We should consider using the sealing grease for valves which do not use sealing grease to improve sealing performance of valve stems.

2. Increasing the packing
We can adopt the method of increasing the packing in order to improve sealing performance of the packing. Usually, we use double-layer packing and multi-layer mixed packing.

3. Replacing the PTFE packing with the graphite packing
PTFE packing is widely used; the working temperature of the PTFE packing is between -20℃ and 200℃, and when PTFE packing's temperature has a great fluctuation range, sealing performance of PTFE packing will be obviously poor; PTFE packing will age fast and have a short service life.

Flexible graphite packing can overcome these shortcomings and have a long service life. Therefore, some factories replace all the PTFE packing with the graphite packing and even replace the PTFE packing of the newly purchased regulating valves with graphite packing. However, there will be exceeded variations and even creeping phenomena at the beginning of using graphite packing; therefore, we need to take the problems above into consideration.
 
breakdowns of valves