[[GQC] Tim]

I had a look this morning in my van, it filled it up all right, hit the flow valve, which in turn activated the shut off manifold. But the whole RO was buzzing like a petrol engine of a lawnmower, all the tubes were vibrating, and there was a loud vibrating sound, like an engine, no joke.

I pushed the float valve down, and up again, and it was gone. Do you think it was the pressure? I'm quite certain I hooked up the shut-off manifold correctly, hopefully it will not have damaged anything. Really weird.

300GPD RO, Van based.

(also if you could please have a look in this thread, and please answer my question on shut off pressure of the Varistream, thanks.)

www.cleanitup.co.uk/smf/index.php?topic=55627.0

[groundhog]

My RO vibrates since I fitted a pump to it, I shouldn't worry about it. I would take the RO out of the van and have a static system, big waste of space in the van imo!!! 

[[GQC] Tim]

My RO vibrates since I fitted a pump to it, I shouldn't worry about it. I would take the RO out of the van and have a static system, big waste of space in the van imo!!! 

True, but it's on the tank cage itself, where normally nothing would be anyway. I don't have the space for an IBC of any sorts, well I have in my parents place, but it's impractical do leave my van there.

I am worried about it, because I do not have a pump, and it vibrates really badly. Can't be good for the membranes. I'm not exaggerating, it's like a petrol engine.

[michael papworth]

This sounds like resonance - and could damage your membrane. Resonance is caused by pressure waves being transmitted through the pipes and bouncing back when they reach an open or closed end. In this case it sounds like the float valve being turned on and off by a standing pressure wave.

(What happens is that the valve closes which causes a small shock which travels as a wave down the pipe and gets reflected back at an end and reaches the valve just as it was starting to rebound - which makes it rebound even more and close with greater force etc. You sometimes hear this in toilet valves when they are just about to close. It can get very bad when the valves get worn.)

DON'T ALLOW THIS TO HAPPEN!!!!

The pressure caused by the waves can go up to VERY high values and destroy seals and membranes in the blink of an eye.

Changing the length of the pipe to the valve might well effect a cure since the standing wave is probably in there.

[[GQC] Tim]

Hm, yea that could be the case, because I've got literally a tiny tube going from the outlet to the float valve, must be 6" or so. Do you think it's that?

[michael papworth]

I wouldn't have thought that making a change on the non-pressured side of the float valve would make a difference - but it might!

The science behind resonance is exact, but finding the causes of resonances (cause of water knock) in a plumbing system ISN'T an exact science!

(Having said that, I'm a scientist, not a plumber.)

If I'm right and it is a resonance (and I could be completely wrong!!!) the problem is more likely to be on the mains pressure side of the valve.

There are three things you can change: The pressure in the pipe, the valve itself or the length of the pipe feeding the valve. The easiest, quickest and cost-free thing to change is the pressure in the pipe.

I'd do this by playing with the stop cock from the rising main. As you close it or open it, you will notice that the resonance gets better or worse, if indeed it IS a resonance.

If it doesn't change, then at least you know to look elsewhere. If it does change, you have isolated the problem and can change either the valve or the pipe.

[groundhog]

I've just remembered that I had a similar problem to this ages ago, the cause of the problem turned out to be the hozelock connector which I had fitted to the tap, it was a stopper and the little valve inside it was bouncing up and down causing the vibrations! I hope this helps. 

[[GQC] Tim]

I've just remembered that I had a similar problem to this ages ago, the cause of the problem turned out to be the hozelock connector which I had fitted to the tap, it was a stopper and the little valve inside it was bouncing up and down causing the vibrations! I hope this helps. 

yea I've got one of them in the system, but that's after the pump, so that can't make that noise.

Thanks Wally, I'm gonna put my thinking cap on armed with your information, and see what the heck is causing it.

btw. What made you choose window cleaning? You said you are a scientist, in what field? Thanks for your help, I appreciate it.

[michael papworth]

Err ... I have an interest in maths, physics and astrophysics.

It colours my approach to almost everything I do, including window cleaning .. which I prefer to my last job.

[michael papworth]

I've just remembered that I had a similar problem to this ages ago, the cause of the problem turned out to be the hozelock connector which I had fitted to the tap, it was a stopper and the little valve inside it was bouncing up and down causing the vibrations! I hope this helps. 

Yes, this is exactly the kind of thing that causes it.

A general principle in physics is that things want to vibrate. Small things vibrate quickly, big things vibrate slowly.

I would imagine that the small valve in a hoselock connector, being small and light, vibrated at a pretty high frequency. Am I right?

[groundhog]

Yes Wally it made a right racket!! It was driving my wife mad so I had to sort it out pronto!!!  It was a bit of a ureka moment when I changed the hozelock connector for one without a valve in it and the vibrations were no more!!!!

[[GQC] Tim]

Put more tubing from the shut off manifold to the float valve, and that has fixed it.

[michael papworth]

So it seems as if it was a resonance and the different length of tube doesn't resonate.

Good. Well done for sorting it.

[[GQC] Tim]

Thanks for your help Wally, really helped me a lot!