"Air Pressure" draining of water pipework - no pressure - am I doing something wrong, or just being dense?

[MH04RMV]

Hi All,
Am attempting to do a "belt and braces" drain down of fresh cold/hot water system using something similar to that shown below, having read and been told of various horror stories of the "extra" water that remains in the pipes freezing, following a normal drain-down, i.e. just opening various dump valves.

I've connected up my compressor (RAC900) to the water inlet and kept an eye on the pressure gauge (don't want to blow joints apart!), but the pressure doesn't appear to increase.
Taps inside are closed, dump valves/taps on external tanks are closed.

Am I doing something wrong, or am I being a bit dense and any air pressure is being lost through the tank overflow outlet, so need to block this up as well (I don't think this step is mentioned in the video)?

Appreciate any thoughts/suggestions.

Cheers,

Rich.

 

[Figaro]

I just open the drain valves, open taps mid point then get my laughing tackle around the tap and blow
Never had a problem.
No experience of your gadget though

 

[lunarman]

Have you got an overflow on the water tank which would need to be sealed to enable pressure to be built up.

 

[Phill D]

a thought!!

if you are connecting to the water inlet and that means where you fill up the tank, then as you say you are likely loosing pressure out of the tank overflow.

i dump the main tank, dump the heater water at the frost valve then i blow through from the shower head pipe. (I remove the head and fit a shrader valve arrangement then blow through opening one tap at a time on both cold then hot.
i then leave the taps open at mid point for hot and cold and remove the drinking water filter.

 

[Phill D]

I just open the drain valves, open taps mid point then get my laughing tackle around the tap and blow
Never had a problem.
No experience of your gadget though

that is exactly as i have done for many years but changed a year or so ago as i had to replace a tap inners as a result of freezing damage. my fault..

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[Landy Andy]

If you are blowing air into the water system with all the taps closed, I think you are asking for trouble personally, but to answer your pressure question, isn’t there an air vent on the tap of the water heater, that would allow the air out ?

 

[DuxDeluxe]

If you have a shurflow diaphragm pump, then I drain the tanks and run the pump with the taps closed until the pump stops (not over pressured as it automatically cuts out) and then open a tap until the pressure goes and no more water. Do this several times progressively with the taps in turn and at the end turn the whole thing off, leaving the taps open. Pretty confident that any water remaining will have been purged out

 

[two]

I think the practice of blowing air through pipes to clear water is flawed.
As soon as air can escape somewhere, it will, and any water remaining in the system will stay there.
You should, perhaps, try blowing from one single tap at a time with the drain open. Even then, you might just end up blowing water along different bits of pipework.
I suggest you fret about the expensive bits, only. Drain the boiler, and clear the taps and pump.
Also remove the filter cover. It's not expensive to replace but they are a common failure and it's easy to remove.

 

[TheBig1]

On a motorhome or indeed a caravan with a water tank, then you need to fit a TEE into the piping after the pump and non return valve, or it will not pressurise. Never go over the 15 PSI limit mentioned and you won't get an issue as that is what the pump runs at

 

[DuxDeluxe]

I think the practice of blowing air through pipes to clear water is flawed.
As soon as air can escape somewhere, it will, and any water remaining in the system will stay there.
You should, perhaps, try blowing from one single tap at a time with the drain open. Even then, you might just end up blowing water along different bits of pipework.
I suggest you fret about the expensive bits, only. Drain the boiler, and clear the taps and pump.
Also remove the filter cover. It's not expensive to replace but they are a common failure and it's easy to remove.

The tank drain is not on the same line as the pump so as long as the tank is empty, you are using the pump to blow air through the lines. Excuse the oil and liquid gas tanker terminology- it is what I relate it to)

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[pappajohn]

The idea is to blow water out, not pressurise the system.
Pressurising the system is asking for trouble.
That type of compressor (rac900 etc)is no use for doing that as it's airflow is too low.
You need some kind of pressure vessel such as on a small 230v compressor then use the contained pressure to blow the pipes out via the taps using piece of wet rag to seal the air hose to tap.

 

[Phill D]

I agree I do not and would avoid blow through without one of the taps open.

 

[autorouter]

Caravan water systems are usually different from MH watersystems, in that they have an external tank, and all the internal pipework is sealed to the atmosphere. A motorhome usually has an internal fresh water tank, and this will have an overflow vent with a tube, to carry away any overflow while filling. That means the trick in the video doesn't work for motorhomes.

There's more than one way to put in a tyre valve, but one good way is to cut the pipe just after the pump, and insert a Tee. Then add a short section of pipe with the tyre valve fixed in it. I put a shutoff tap between the Tee and the valve, but it's not strictly necessary.

Most water systems work at between 1 and 2 bar pressure (15 to 30 psi), and the water heater tank can usually stand 2 bar minimum. Pressurising it with a digital compressor that limits at 15 or 20 psi will do no harm. If the compressor doesn't self-limit, then keeping one tap open all the time might be OK, if you're feeling lucky.

 

[two]

I agree that, if you're determined to do this kind of thing, a high volume of air rather than high pressure is what's needed.
I also think you should not try to work against gravity; blow from each tap towards the drain.
A good pair of lungs maybe all you need.
Even then, I'm sure you'll not remove all the water from the system, just a little bit more.

 

[the1andonly]

I use a low pressure high volume pump (ie air bed pump fixed to a Tee and shurflo closed off.) to blow through the system one tap at a time.

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[DuxDeluxe]

The idea is to blow water out, not pressurise the system.
Pressurising the system is asking for trouble.
That type of compressor (rac900 etc)is no use for doing that as it's airflow is too low.
You need some kind of pressure vessel such as on a small 230v compressor then use the contained pressure to blow the pipes out via the taps using piece of wet rag to seal the air hose to tap.

….or as previously described, simply use the Shurflo pump if you have one to do it all in perfect safety for you at zero cost and minimal effort. It works on ships as well

I would like to know a reason why I cannot do this……..