oliverpsmile wrote:Small amount of water in the piping system is harmless. It freezes but does not do any damage (for example the water heater tank contains always some water left). As far as the pump is concern, blowing air and running the pump evacuates enough water, so no damage could occur.
Oliver, I do this 2-5 times a year and have been doing it for 20 years now. I use to assume that applying 40 psi to the city water hook-up and running the water pump was enough to clear the pump. A few years back I found stress cracks in the water pump - it obviously had freeze damage. This configuration does not result in a high volume of air flow through the pump as it does at the faucets and drain valves.
Since then I've found an easy and effective Solution. After clearing the lines, final task is to isolate and blow out the pump. Disconnect the input and output lines to the pump, hold a rubber tipped dust blower to the input side of the pump and with the pump turned on blow air into it. A strategically placed sponge near the output side catches a couple of tbsps and you hear the pump sound change from gurgling to a hum.
oliverpsmile wrote: Very recently I built a trap (1.5" PVC pipe), filled it with water and put it in the freezer. The ice expanded alongside the pipe and did not rupture anything.
2 or 3 of us on this forum have experiences that prove your experiment doesn't always replicate the real world. The shower drain in the 26' RSB hangs exposed under the rear of the coach. One cold day on a 5K' mountain pass I noted the BF rear view mirror thermometer unexpectedly dipped below freezing for a few minutes. When we got home I noticed it dripping on the barn floor. 'Easy and cheap to replace but lesson learned!
oliverpsmile wrote: So it is more than enough to drain the system driving with all spigots open (it safes time). And to be on the safe side, blow with with 45 psi air and put some of the Wal Mart stuff in the traps. With spigots and drain valves open the BF can go safely for storage.
Oliver is correct on the face of it but it should be noted that even though the process is easy to perform and can be done in just a few minutes it isn't mindlessly simple nor intuitive.
Be smart. Be safe
Please follow the instructions posted in the link recommended by Trish (:?:) in this thread. There is a lot of misinformation posted on the web - most of it is simply misleading due to a lack of detail. As an example: One could easily assume that you could hook an air/tire pump to the city inlet and open all the faucets and blow. When water no longer comes out of the faucets the process is complete -right? This would likely not end well. A) It could turn your water heater into a bomb if the pump were left on while connected to a closed system. (The WH does have a safety valve but why temp fate?) B) Most likely, it would simply not dry the lines well enough to protect against freeze damage.
A compressor with an air tank and regulator is required and one must follow the explicitly ordered process designed to chase the water from the system's head to the drain valves.