Question for "Blow Out the Water Line" gurus

Empty Nest, Soon wrote:

Gdetrailer wrote:
. . .
I would not recommend 90 or 100 lbs on the city water line, that is well above normal water line operating pressure even for city water.

Air compresses greatly and over pressurizing water lines with air will create potential safety hazards when a waterline or even water fixture fractures or ruptures.

Use the regulator on the compressor, if you don't have a air regulator buy one and USE IT..

Set the regulator to zero then increase slowly up to 30 lbs and not much more than 40 lbs.. This is the most gentle way to introduce air pressure.

You really don't need the high pressure to do this, but what you need is VOLUME which is rated in CFM.. In air compressors you tend to be rated more CFM at LOWER PRESSURES.. So the lower pressure you set the regulator the more CFM a air compressor will be able to supply..

Using low pressures like 25 lbs to 30 lbs allows very small "pancake" compressors like this one from Harbor Freight to safely empty the lines..



Even though it only can supply 1 CFM at 40 PSI and is often "on sale" for $39 or $49..

It just takes a longer time for the compressor to build up and the motor will run more but you will only be running it 10-30 minutes max..

Perhaps I need to clarify . . .

I was not suggesting pumping up the RV water system to 90 or 100 pounds. I start with my portable air tank at that pressure.

The RV water system will never see anything close to 90 PSI because the compressed air first expands into the empty water heater (now 10 gallons; my last one was 6 gallons) and the pressure will be cut by about half when it equalizes into about twice its original volume.

I start with pressure that high for the sole reason of getting a greater volume of air into the portable tank before beginning. I could get the same amount of air by filling the portable tank to 45 or 50 PSI twice.

Note: For blowing out the lines, I use a 7-gallon portable air tank, not my compressor directly. If I should need more air than what is in the little tank, I will take it back to my workshop and refill from the compressor. I don’t hook up the high-pressure compressor to the water system directly.

I agree that volume of air is what’s important. The higher starting pressure in the portable tank is simply my way of getting volume of air with fewer refills of the portable tank.

Wayne

I would still recommend using a regulator even with a portable tank..

This allows you to turn on the air at a slow controlled rate instead of shocking the water system..

Fortunately for myself I can reach my RV via 75ft of air line.. Otherwise I would use my small pancake compressor.. Doing so eliminates the short coming of a small air tank supply.