Water inlet restriction or ?.

[budbon]

I bought my 2019 2250rk from a private party this winter. Not being sure he had properly winterized, I began a check this past week. I have an adapter I made to winterize using air compressor (set at 40 lb.) I have used this for years on other RV's. When I hooked the air line to the inlet, I was unable to get pressure to go thru the lines. Assuming there is ice in the lines (it has been 10-20 degrees here in Colorado) I set about warming everything. Two days later, still unable. To pressure the lines. Is there a check valve or some such that could be blocking the inlet?
Today I am going to pressurize the system thru the water heater to attempt a backflush test to ensure the lines are without restriction. In the meantime, any suggestions would be appreciated.

[huntr70]

Can you pull the screen out of the inlet and look for the check valve?

You can push it in (make sure it is not under pressure or you'll be putting a new one in).

[budbon]

I put the adapter on the water heater pressure relief valve and put 40 lb air pressure on the lines. I discovered the water lines were okay. I then put the adapter back on the water inlet and everything is working. That releif valve must have been stuck. Thanks for the response.

[boyscout]

I put the adapter on the water heater pressure relief valve and put 40 lb air pressure on the lines. I discovered the water lines were okay. I then put the adapter back on the water inlet and everything is working. That releif valve must have been stuck. Thanks for the response.

Congrats on solving your problem.

An engineer has told me that 40 lb of air pressure puts a lot more stress on the plumbing system than 40 lb of water pressure. I've seen similar cautions elsewhere since. I use 20 lb of air pressure when blowing lines and it works fine.

[Chewwi]

Congrats on solving your problem.

An engineer has told me that 40 lb of air pressure puts a lot more stress on the plumbing system than 40 lb of water pressure. I've seen similar cautions elsewhere since. I use 20 lb of air pressure when blowing lines and it works fine.

What’s heavier 40 lbs of water or 40 lbs of air?


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[Richter]

Mass (weight) is not the same thing as pressure. The problem is a liquid (in this case water) has some compressability whereas a gas (air) does not.

I’m not certain that I understand that, but...

It would seem to me that, if you turn on the air pressure with the faucets open, you are not allowing 40 pounds of pressure to build up in the system. You are not pressing against a fixed object (a closed valve), but against a movable object (water). As long as you are pushing water through the system, and out an open valve, I don’t see that there would be as much pressure build-up as when I keep the pedestal water on and there is 40 pounds of actual constant pressure in the system.

[Chewwi]

Mass (weight) is not the same thing as pressure. The problem is a liquid (in this case water) has some compressability whereas a gas (air) does not.

True! Mass weight and pressure are NOT the same. 40 lbs of lead and 40 lbs or cotton weigh the same. 40 psig of water and 40 psig have the same pressure. 40 psig of pressure is NOT THE same as 40 lbm.

You have it backwards. Water (H2O in its liquid state) is virtually incompressable. Air is very compressable, as are all gases.

Their is a reason you have air in your tires and not water. Water filled tires would make for a very rough ride.

[budbon]

Congrats on solving your problem.

An engineer has told me that 40 lb of air pressure puts a lot more stress on the plumbing system than 40 lb of water pressure. I've seen similar cautions elsewhere since. I use 20 lb of air pressure when blowing lines and it works fine.

All I can say is I have used this 40 lb air pressure on my last 4 RV's plus this one and have yet to blow out any lines. Maybe I am just lucky or maybe the lines are capable of holding that much air pressure. It is interesting that when a new home is built, the plumbing inspector wants to see all of the new lines hold a set value under air pressure. It would be interesting to see air pressure tests done on RV lines.

[boyscout]

It would seem to me that, if you turn on the air pressure with the faucets open, you are not allowing 40 pounds of pressure to build up in the system. You are not pressing against a fixed object (a closed valve), but against a movable object (water). As long as you are pushing water through the system, and out an open valve, I don’t see that there would be as much pressure build-up as when I keep the pedestal water on and there is 40 pounds of actual constant pressure in the system.

However is that how you blow out your lines? Leave faucets open?

I keep all outlets closed and open the faucets and other outlets one at a time, allowing pressure to build as I move from one to the next so there's a good sputtering burst of water and air when I open the outlet.

The person who advised me to use air pressure lower than the 40-50 psi water pressure that our plumbing is designed for was @Cate&Rob, longtime plumbing guru and helpful advisor here and on another forum. That tag I inserted in the last sentence may bring him to this thread to explain the advice better than I can.

However as I've said, when I set my regulator to 20-25 psi of air pressure it does the job just fine; don't know why I'd use more.

[powerscol]

Mass (weight) is not the same thing as pressure. The problem is a liquid (in this case water) has some compressability whereas a gas (air) does not.

Its actually the other way around Water is essentially in-compressible just like hydraulic fluid while air is (scuba tanks come to mind). If air was in compressible, then why do brake lines need to be bled of it to work properly and not feel spongy?

Now pressure is pressure, Force over an area, So 40psi air is the same as 40 psi of water or a 40 lb mass over a square in area. However as it flows through a faucet air will move (velocity) faster as is has less resistance, so it is precieved as having more force. The high velocity can cause damage to seals etc, so I don't use more than 20/25 psi.