DrewE wrote:
Just curious and thinking out loud here...
Aren't there seals on either side of the gate of the gate valve? Assuming my understanding of that is correct, what keeps the seals on the downstream side wet and hence in good shape? I'd think if being moist was a requirement that we'd see far more cases of seals breaking down on one side but not the other of the valve.
I would tend to suspect that seals mostly wear out from aging rather than being dry, but I'm certainly no expert on the chemical properties of rubber or rubber-like gaskets.
Here's a look at a gate valve:
The seals (#3) aren't anchored very securely on the body of the valve - if you remove the 4 bolts that hold it together, the seals will simply fall off. If they dry and get "grabby", or shrink/change shape, etc, they can get in front of the blade, and then the valve no longer closes fully. Ironically, antifreeze is "slippery", so helps lubricate the seals (as do specific products sold for RVs). The only time I would have to do seal replacements was on tubs that had been left sitting without water and the gate valves left open.
I'm personally not comfortable with the thought that my black/gray tank gate valves might not close properly, when about a dollar's worth of antifreeze will prevent a potential problem.
