RV plumbing freeze test

[roach711]

I have both PEX and vinyl braided tubing in our bus and even though I winterize the plumbing each fall (by sucking out the water with my shop vac) I still wondered what might happen if I didn't get all the water out of the system.

I had read that PEX tubing is freeze resistant but what does that mean? So, since I'm now semi-retired and have way too much time on my hands, I decided to do a test.

I cut a piece of 3/4" PEX, filled it with water, formed it into a circle then crimped the connector rings with a small PEX crimp tool. I did more or less the same with some 1/2" vinyl braided tubing I had laying around except I used hose clamps to seal the connector. As a control I also soldered end caps on to a length of 1/2" copper pipe. All three were assembled under water to make sure no air remained inside then I put them outside overnight in 10 degree (Fahrenheit) cold.

My expectation was that the copper pipe would fail outright and that the vinyl braided tubing would hold. I thought the PEX tubing would also hold but wanted to see for myself since I'm considering upgrading our home plumbing.

Here are the three test rigs



Here's the PEX crimp tool with crimp rings



The next morning I checked our intrepid test subjects and found the copper pipe had failed. No surprise there. What did surprise was that the end cap had been pushed off. The solder joint failed because of (ahem) operator error. I was freezing my butt off in the cold garage and hurried through the job ending up with a bad solder joint. I might just re-do this one and re test. It seems we never outgrow that love of wanton destruction.



The PEX piece was still intact with some barely noticeable swelling near one side of the crimp joint and the vinyl braided tubing piece had just shrugged off the ice. It appears to have minimally expanded over it's entire length and just handled the situation.

So it looks like both the PEX and the vinyl braided tubing will be quite suitable in a situation where pipes might freeze. The PEX is stiff and difficult to bend while the vinyl braided tubing is quite flexible. The vinyl is rated at 250psi so it's plenty strong. If I had it to do over again I would use the vinyl tubing exclusively as water supply piping.

Regardless, I'll still be trying to get as much water out of the system as possible when winterizing. The plastic pipes and tank will all be fine with a little ice in low spots but the water pump, sink/shower traps and water heater would likely be damaged if left filled over the winter.

[Redbear]

Thanks for the test. The experience I had with an RV at work was that the plastic impeller housing on the water pump split from not being fully drained, and ruined the pump. Since the pump is usually one of the more expensive parts of the water system, that experience has (over?) sensitized me to that particular failure. I personally would put the pump at the top of the list for inspection and protection.

If I were winterizing an RV, I might even disconnect the pump for the winter.

But I also have experience with copper pipes splitting lengthwise in back room of a house when I was away, and the furnace was turned down too low to sufficiently get out to the back. Those pipes are now PEX.

[roach711]

I built our plumbing such that the water tank and the water heater are on opposite ends of the runs and are the low points so water tries to run back to them an not pool anywhere in the pipes. Both the tank and the water heater have drains so a lot of water drains out on its own, but it surprised me when I used the shop vac to suck out the water heater. There was something like a gallon or so left after draining. Another thing I found was that the water pump stops the water from draining back to the tank so now I disconnect the inlet and outlet connectors and run the pump for a second to clear it. I also remove the little strainer thingy on the pump and leave it off all winter.

I did building maintenance most of my life and between split pipes, sump pump floods and roof leaks from ice dams I've come to despise water. Except for drinking and bathing I'd gladly live without it altogether.

[gbstewart]

when I winterize my bus, I disconnect the water pump from the fresh water tank and place the intake tube into a gal of pink rv antifreeze I bypass the hot water tank, then turn on the taps starting at the kitchen, bathroom , etc till pink is running out of all the taps ant toilet, takes about 2 gals reconnect to fresh water tank and wait till spring. I used all pex pipe, and im renovating one of my rental houses and using pex. had a copper pipe break from ice, not using that anymore, pex only
gbstewart

[nat_ster]

Great test Roach.

I have seen a fair bit of frozen, water filled pex. Here are my findings.

If the system was pressurized before freezing, it compounds the expansion. At 60psi or more, it gets ugly.

Brass fittings always fail first. I think this is why one pex manufacturer is turning to fittings and rings made of the same cross linked material.

The pex will never burst. It simply expands, mostly lengthwise. If we froze 100 feet of water filled pex, it would be around 115 feet frozen.

As far as the vinyl braided tubing, it will fail in less than a year in any case where there is heat involved. Even in cold environments, the hose clamp system is subject to leaking, expensive clamps, smells the water up, and IMO will fail long before the pex. It's a much older technology, not suitable for potable water.

Nat

[roach711]

Thanx Nat - Good to have your insight here.

I would not have guessed that the brass PEX fittings would fail first or that the pipe would expand lengthwise. Come to think of it, though, I would rather have the fitting fail since those are all in accessible spots. I did consider the effect of line pressure in addition to the freezing but had no practical way to pressurize the test pieces. Besides, we don't have a city water hookup so our working line pressure is pretty low.

Time will tell on the braided vinyl tubing. Watts (the manufacturer) lists it as food grade but doesn't make any claims as to tastes imparted to the water. We'll check that out this summer and if taste is a problem I'll replace the vinyl with some new faucet supply lines.

[JakeC]

Originally Posted by roach711

Thanx Nat - Good to have your insight here.

I would not have guessed that the brass PEX fittings would fail first or that the pipe would expand lengthwise. Come to think of it, though, I would rather have the fitting fail since those are all in accessible spots. I did consider the effect of line pressure in addition to the freezing but had no practical way to pressurize the test pieces. Besides, we don't have a city water hookup so our working line pressure is pretty low.

Time will tell on the braided vinyl tubing. Watts (the manufacturer) lists it as food grade but doesn't make any claims as to tastes imparted to the water. We'll check that out this summer and if taste is a problem I'll replace the vinyl with some new faucet supply lines.

The problem in my experience with vinyl is that it does not handle temp cycles well, over time. It seems to start to deteriorate. I'm not saying it won't work in a bus/rv environment, but pex is hands down superior for longevity.

[Diesel Dan]

I've had many problems with systems that involve hose clamps eventually leaking, if not fluid, then air. I know air leakage is probably not so much of a problem for water delivery, but at this point, I look for any other solution to avoid using hose clamps. I will be using PEX in my bus.

[ol trunt]

Roach, from now on you will be known as "Dr. Science". Its good to see an analytical approach to our bus stuff. Don't leave the lab--keep up the good work! Jack

[roach711]

Originally Posted by ol trunt

Roach, from now on you will be known as "Dr. Science". Its good to see an analytical approach to our bus stuff. Don't leave the lab--keep up the good work! Jack

The scientific approach is fine - it answered the question at hand - but there's nothing like having long personal experience with the stuff. I remember long ago reading that from an engineering standpoint, a bumblebee shouldn't be able to fly. Fortunately, bumblebees don't care what engineers think.

On the other hand, I don't automatically assume someone who's "in the trenches" has it right either. Last year we had a boiler tech out to certify the safety controls on our hot water boilers and as I was standing there he turned the boiler high limit down from 230 degrees down to 210. When I asked him why he set it so low he said that water boils at 212 degrees and that boiling would damage the boiler. I had to explain to him the effect of pressure on the boiling point of water. Needless to say, when we did need repairs I called someone else.

[JakeC]

Originally Posted by roach711

The scientific approach is fine - it answered the question at hand - but there's nothing like having long personal experience with the stuff. I remember long ago reading that from an engineering standpoint, a bumblebee shouldn't be able to fly. Fortunately, bumblebees don't care what engineers think.

On the other hand, I don't automatically assume someone who's "in the trenches" has it right either. Last year we had a boiler tech out to certify the safety controls on our hot water boilers and as I was standing there he turned the boiler high limit down from 230 degrees down to 210. When I asked him why he set it so low he said that water boils at 212 degrees and that boiling would damage the boiler. I had to explain to him the effect of pressure on the boiling point of water. Needless to say, when we did need repairs I called someone else.

HAHAHAHA!!!! That is awesome. I've personally heated water up to 260* in a pressurized, closed loop heating system. It was a little scary when a hose blew, though Especially when I was standing right there. In a t-shirt. -_-

[Redbear]

Originally Posted by roach711

. . . I had to explain to him the effect of pressure on the boiling point of water. Needless to say, when we did need repairs I called someone else.

Would it blow his mind to learn that propane boils at roughly -44°F (-42°C), and pressure keeps it liquid on a hot summer day?

[roach711]

Originally Posted by Redbear

Would it blow his mind to learn that propane boils at roughly -44°F (-42°C), and pressure keeps it liquid on a hot summer day?

Never mind him, that blows MY mind.