water pressure vs air pressure

[captmello]

I found myself tasked with winterizing a property the other day. it has a well that feeds 3 structures. I found that I could isolate the lines to each building using the different valves built into the plumbing setup. there is an old non-bladder expansion tank that I was charging up to 20 psi with my compressor before releasing the air pressure to one of the buildings to blow out the water. the tank is galvanized steel and typically is pressurized to 50 psi when the water pump is on.
it would have been helpful to charge the tank up more than 20psi but it made me nervous. could I pressurize the tank to 50 psi with air like it is with water? or is there a difference?

 

[alldodge]

PSI Pressure from water or air is the same, only difference is air may leak out some place where water would not

 

[harringtondav]

It would best to know the on-off/start-stop pressure settings of the system's pump control switch. Most have a gage showing actual pressure. If you can find this, force the pump to start by running water from the system until the pump cycles on, and observe the pressure at pump stop. You'll then know the safe pressure for the tank. Seems you already know it is 50 psi. If so charge it to 50 psi. Pressure is pressure. Difference is if the tank fails with water it will leak. With air it will explode.
Our river house's well system is set to 50-70 psi limited by the pressure relief valve on the bladder pressure tank. I bleed the system to zero the to empty the pressure tank, and cut it out. Then I charge the water heater to the compressor's 120 psi limit. ....water heater is rated for 200 psi. Then I use the water heater tank for a pressure vessel to blow the system dry. And man, does it ever blow!

 

[dwco5051]

During normal operation the tank has both water and a cushion of air. The tank's integrity is not changed by what is causing the pressure. If there would be a catastrophic failure of the tank the potential energy would be more if it was 100% air than say 75% non compressible water and 25% air.

 

[captmello]

thanks for the replies. next year I'll install an air hose fitting so I can attach my compressor, set to 50 psi, to the expansion tank to make the winterizing easier.
I'll leave the 120 psi to harringtondav.

 

[harringtondav]

thanks for the replies. next year I'll install an air hose fitting so I can attach my compressor, set to 50 psi, to the expansion tank to make the winterizing easier.
I'll leave the 120 psi to harringtondav.

I winterized my wife's family cabin for years before we bought our own 13 yrs ago. Her cabin looked like Rube Goldberg ran the plumbing. Impossible to gravity drain with broken copper somewhere every spring. We replaced the drywall in front of the pipes with removable peg board to simplify the repairs.
After I went to 120 psi no more broken pipes.
I recently finished the lower level of our place with nearly water pipe behind drywall. I sleep well over winter confident things will be intact in the spring.

 

[dingbat]

thanks for the replies. next year I'll install an air hose fitting so I can attach my compressor, set to 50 psi, to the expansion tank to make the winterizing easier.

Blowing out lines is a function of flow not pressure.

You would be better off installing a schrader valve in the line and forego pressuring the storage tank all together.

Used this method to clear the water line running out to the barns for years before running new lines at the proper depth a few years back

 

[dwco5051]

Blowing out lines is a function of flow not pressure.

Used this method to clear the water line running out to the barns for years before running new lines at the proper depth a few years back

Reading this post reminded me that I hadn't drained the water line to my shop and garage yet. Since it is slightly downhill I just blew it out with the shop vac.

 

[dingbat]

Since it is slightly downhill I just blew it out with the shop vac.

I use a shop vac to clear (suck) the water out of the 1.5" lines running between the skimmers in the pool and the pool house.

Actually works quite well considering the lines are 50-60 ft. long and 5 ft. below the ground level at their deepest point

 

[alldodge]

I use shop vac on AC condensate line every other year.

 

[harringtondav]

Blowing out lines is a function of flow not pressure.

You would be better off installing a schrader valve in the line and forego pressuring the storage tank all together.

Used this method to clear the water line running out to the barns for years before running new lines at the proper depth a few years back

I agree that air flow is what makes it work.
In my reply I mentioned charging our empty water heater to 120 psi as a large pressure tank to blow out all lines in our Summer house. The 120 psi doesn't last long. As the blow out process moves from fixture to fixture the pressure drops fast.
When I started winterizing over 20 yrs ago I just charged up my 20 gal air compressor to shut off and started blowing. It didn't take long until it was back on full time and loosing ground on the pressure gage until it couldn't keep up.
So my 50 gal water heater, and @captmello ,s tank are just additional pressure tanks to keep the air flow going until the last line blows clear.

 

[captmello]

So my 50 gal water heater, and @captmello ,s tank are just additional pressure tanks to keep the air flow going until the last line blows clear.

Yep. I found that it took about 10psi to move the water in the lines, so charging to 20 moved some water but I had to recharge quite often to clear each line. I'm confident that next year when I charge up to 50psi, it will speed things up, and by hooking my compressor to the expansion tank, I can leave it running while I move from building to building.
Winter is finally here in MN.

 

[harringtondav]

Winter is finally here in MN.

...we are right behind you in east central IA. Won't be able to winterize the heated place until 21 Dec. 200+ mi round trip could be a pain that time of year.

 

[Renken2000Classic]

I use shop vac on AC condensate line every other year.

That's a good idea. Mine was somewhat clogged when I changed the blower assembly last summer. It's right by the water heater, which I've been meaning to drain for a few years now...