plumbingwater-heater
Had a bit of a snafu at home today that resulted in an empty 75 gallon tank getting refilled without opening a faucet. Faucet was opened only after the tank was full, which resulted in a long burst of pressurized air coming out. I'm worried this pressurized air may have caused damage to the pipes, fittings or fixtures. Could this be the case? These are copper pipes, some 3/4'', some 1/2'', in a 4,500 sq ft home.
UPDATE: For what it's worth, few weeks have passed and no leaks to be seen.
This sounds like your leach field is possibly blocked. That's the disaster scenario where you not only need the tank pumped, but the yard dug up and a new field placed.
Water from your laundry coming up in your tub is a sign that it's not draining to the septic system. This is either because there is a block in the system before the tank or because the tank is unable to accept any more water as it is plugged on the discharge / leach field side.
When I opened up the clean out pipe clear water came out (about ten gallons). I shoved the hose down about 25 feet and it was running full force but it seemed like all the water coming out of the hose was draining back out of the clean out pipe.
... and that's the sign that it's doing option #2: the tank is full and failing to drain.
20 years old, it's almost certainly time for a new one unless it's of very unusual construction - like stainless steel.
If water:
overflows from the top of the pipe onto the floor
Then the overflow pipe is not correctly routed - it should go DIRECTLY down to the floor. I can see it going sideways in the picture on your other question. It also appears to be reduced in size, which is a code violation, and if it's positioned so that water is held (trapped) in it, that's a code violation.
Many hot water heaters need an expansion tank to avoid over-pressurizing the PRV when heating a slug of cold water when no water is being used. Most PRVs are rather bad about resealing when they have been "exercised" a bit. Both of these may play into your problem.
Best Answer
I wouldn't worry about it at all. A gallon of water is roughly 213 cubic inches. Assuming that you filled the tank completely (which is unlikely - see below), you would have displaced 213 * 75, or 15,975 cubic inches of air inside your plumbing. One atmosphere of pressure (14.7 psi) is defined as the pressure exerted by a 33.8 ft column of water. Assuming that all of the pipe in question is 3/4", you would have increased the pressure by 14.7 psi if the total pipe length was 472 feet.
But what actually happened is that the tank stopped filling when the air pressure reached equilibrium with the water pressure. The water that you filled the tank with was coming in at whatever pressure that your household water supply has (typically this is somewhere around 40psi). When the total pressure in the plumbing system reaches 40psi, the tank simply stops filling because there isn't a pressure differential. So basically, once the air you were displacing reached the pressure of your water supply, it would have simply stopped compressing it because the tank wouldn't be filling any more.