Cracked multiport valve

[essayer]

Anyone seen this before? The return line spigot on our multiport has developed a crack seemingly since last summer. Drips constantly with filter on.

Line was drained for winter and the equipment room probably never went below freezing, so absent some mechanical damage I wasn’t aware of, why would it have cracked like this?

Is a repair possible?

 

[ajw22]

Post some wider views of the MPV and the area of the crack.

 

[essayer]

 

[ajw22]

I don't think any repair will hold long term.

Time for a new MPV.

 

[essayer]

Boo! But I think you’re right.
What might have caused it? Physical damage?

 

[ajw22]

How old is the MPV?

Plastic gets brittle with age and UV exposure.

 

[1poolman1]

No repair possible, sorry. Part of the problem is that the fittings were threaded all the way in. Pipe nipple threads are tapered to expand as they go further in. The socket has the same taper, smaller the further in you go. An old adage I learned 40+ years ago is, "Never less than 3 nor more than 5." You should never see less than three threads outside the fitting socket, nor more than five. With a good 5 or 6 tight wraps of Teflon tape this has never failed me. You can add a bit of RTV silicone as well, it always helps.

 

[essayer]

The MPV predates my ownership but I think it’s 5-10 years old.

Thanks 1poolman1 I will be careful on reassembly!

One last question - the existing pipe work seems to have some flexible rubbery sealant around it - you can just about see it on the photos. What is it? Is it required?

 

[1poolman1]

Looks like someone tried to seal a leak with RTV (silicone) sealant. If its not in the threaded area its just in the way. Peel it off.
Personally, after I wrap pipe threads with Teflon tape I will, on fittings this size, put a very thin layer of RTV as an added precaution. That's just my standard procedure. Be sure to use unions to re-assemble. The hi-temp pump unions that use an O ring to seal work very well. I still add about 4 or 5 wraps of Teflon tape to the threads, but I hate call-backs.

 

[essayer]

With nothing to lose I remade the whole thing with fresh pipe sealant but still a slight drip. So I’ll replace the valve, but one weird thing.

I tightened up the fitting dry, and six turns was finger tight. Literally just using my thumb and finger to tighten. Everything I’ve read says to go one and a quarter past this, so I remade with sealant, and got an extra half turn on reasonably easily using my hands. Another quarter turn by hand led to a nasty cracking noise and some surface cracks all around the edges of the female thread opening up!

So I can’t imagine going a full one+quarter without it causing serious damage. Before I break another multiport valve, is this just because the port is already fatigued or have I misunderstood the various instructions?

 

[ajw22]

Everything I’ve read says to go one and a quarter past this, so I remade with sealant, and got an extra half turn on reasonably easily using my hands.

Where did you read 1 + 1/4 turn more?

I would have said 1/4 turn after hand tightening.