threaded plug blew out of plumbing line

[Maryland_Newbie]

Hello, I've been helping my next door neighbor with her pool (new as of this season). But we made a mistake today. After we added a chlorine tablet to her chlorinator, we forgot to reopen the valve next to the chlorinator, and we turned the pool pump back on with that valve closed. We did not realize the mistake for some hours, until the pool level had dropped below the level of the skimmer basket intake. When we checked the pumping equipment area, we saw that a threaded plug had blown out of the line. We think this plug might have been designed for this purpose, to release pressure from the system in case of a valve mishap, in order to protect the equipment. We can see no other purpose for that plug, which is in the pipe exiting near the base of the (DE) filter.

The company that installed the pool has closed for the weekend, so we were hoping to troubleshoot ourselves. We saw that there was a lot of teflon tape wrapped on the threads (the old tape now shredded and adhering to the threads inside the pipe opening). We also saw a ring of what appeared to be silicon caulk, which seemed to fit the shape of the end of the threaded plug and the base of the threaded opening in the line.

We tried wrapping several layers of teflon tape around the threads and twisted the plug into the opening. We didn't know if we should tighten it firmly or not, if its purpose was to permit a pressure release if needed in the future. When we restarted the system, after the pump was primed, there was a small amount of water leaking around the threads. We tightened it more securely and water continued to leak. So we shut down the system for the time being.

My questions are:

1) If caulk is needed as well as teflon tape, what kind of caulk would be appropriate to add to the threaded area; where should we apply it; and how long would it need to cure before we could test the system again? How tightly should this threaded plug be tightened if it is meant as an emergency pressure release?

2) Can you tell me if this threaded plug does seem to be intended as an emergency pressure release? Or was it meant instead as part of the set-up for winterizing the pool or some other purpose? If it is not designed for emergency pressure release, then do you think the threads have been damaged by this trauma?

3) Do you think we have caused damage to the pump or the filter by creating the pressure build-up that caused this threaded plug to blow out and by continuing to run the system (with the closed valve and with water escaping through the open pipe) for about six hours after that? In other words, even if we are able to get the threaded plug to stop leaking, is it a bad idea to run the system at this point; are we better off bringing in a professional to inspect the filter, etc.? Would we have damaged the heater if it were running under these unfortunate circumstances?

Thank you for helping out these pool newbies!

[Teapot]

I won't answer all of your long post, sufficient to say no threaded plug would ever be used as a pressure relief device as it could injure someone used in the way you describe. A modified polymer sealant from home depot (not silicon) could be used as caulk around the thread and setting time will be as detailed by the manufacturer.

If the pump can deliver such a pressure to blow out a properly fitted threaded plug the the pump is too powerful and the system will be inefficient and cost more than it should to run.

[Denniswiseman]

I agree with Teapot
If the pressure was high enough to blow out a threaded plug then yes the threads would be damaged
I take it that the plug is plastic and what it screws into plastic. See what threads are damaged and get a brass plug
Your heater normally has a minimum flow rate through it to operate
Other damage can only be determined when you try to run it