Taper threads require a thread sealant for lubrication to prevent damage from galling and seizing during assembly. Thread sealants also fill any voids between the two threads that could cause a spiral leak.
Cylinder valve standards related to installing cylinder valves with taper threads into the cylinders allow both PTFE tape and paste to be used as a thread sealant. However, PTFE tapes are much more commonly used in the gas industry than paste. My experience is that most users are not aware of the possibility of using thread sealant paste.
Both methods have their advantages and disadvantages, and being aware of them is the first step in making an informed choice about their usage. In both cases, it is essential to choose the proper specification of thread sealants to ensure compatibility with the cylinder valve, cylinder, and the gas service/s for which the valve shall be used.
Benefits of Thread sealant paste:
- Unlike PTFE tape, which has to be removed before re-application, thread sealant pastes (like Krytox™ TS4) can be reapplied over the existing paste.
- Pastes easily cling to threads and do not shred or tear during assembly /disassembly.
- Pastes are easier and faster to apply on the threads, unlike tapes that need operator skill to ensure the correct taping procedure is followed (unless the taping process is automated).
Benefits of PTFE tape:
- PTFE tapes are more forgiving to machining inaccuracy, and they tend to assist in making the thread joint leak proof even if the threads are machined slightly out of specification.
The cost-effectiveness of both solutions has to be evaluated case by case by the user. Either solution may prove cost-effective depending upon variables not limited to the thread sealant cost, labour cost, quantity, and how frequently the cylinder valves are required to be uninstalled and reinstalled into the cylinder.
Supposing users responsible for installing cylinder valves into cylinders have never used or evaluated the possibility of using paste as a cost-effective thread sealant, I encourage them to give it a try.
