Water filtration thumping problem

[Electron Spin]

I have an old under the sink H2O water filtration system. Its main components are 2 cylinder type filters, one 2.5 gal. storage tank, one passive mechanical "switch" plus a birds nest of plastic tubing with zero leaks anywhere. The output (dispenser) is your standard gooseneck type with a plastic lever to allow water output.

This is the problem: After I output water everything is normal, no hydro thumping, then after abt 5 minutes I hear and can feel to the touch this thumping at about every 900-950 ms.. a bit faster than one unit of time. It will thump until the cows come home if I do nothing.

This has been going on for years! I kid you not, no problems except for that blasted noise. It's driving me nuts!

One way I have been able to stop it is by turning on the output slowly then turning the lever down very, very slowly until the small stream of water starts to drip and then very, very slowly stopping the drip until no more output.

My method seems to work abt half the time. I do believe, but without any scientific method to back me up, that slamming the water off during a full-on output could cause air in the line thus the thumping, but that's just a guess.

People, this has been driving me nuts for a long while and hydraulic thumping in my world can be very, very bad.

Thanks in advance for any ideas or possible solutions.
Physics rules!

Alex

 

[sandy stone]

What is the source of water pressure in your system? What is the switch for?

 

[Electron Spin]

The source is from the city water system that supplies the cold water to the main faucet.

The passive "switch" or one way/2 way valves is connected to the main 2.5 gal tank and the 3 filters.

It is about 1 inch high and 4" in for Y and X.

The two vertical filters are cylindrical pre-filters abt 6' by 3" dia.

If I were to make an analogy the whole mess might be represented by an electrical series/parallel circuit as shown.

Sorry in advance for the nasty depiction. I am totally embarrassed but I welcome shame.

 

[anorlunda]

It sounds like water hammer. Are you familiar with that? Try this article.
https://en.wikipedia.org/wiki/Water_hammer

 

[Electron Spin]

It sounds like water hammer. Are you familiar with that? Try this article.
https://en.wikipedia.org/wiki/Water_hammer

Thank you anorlunda, Yes indeed. I forgot to mention that I do have a water dampener under the sink before any cold water outputs or appliances.

Yes, as a petroleum engineer, mostly drilling, this thumping or hammering was one of my first thoughts. Alas, then I would open up the output valve I tried closing it very, very, slowly down to a very small dribble to a singular drop that would reside in/on the mouth due to the water tension just to make sure I had no air inside the system which did not work.

Incidentally, to give one an idea on its intensity, one can hear it abt. 30 feet away and the frequency is always the same, between about 900 ~ 950 ms.

Another tidbit is that the intensity of the thumping can and does change after a good period of time but not the frequency, never the frequency.

One more thing, The 2.5 reserve tank has a auto tire type pressure nipple and the measured pressure is HOLD EVERYTHING! I have zero to just a few pounds of pressure.. I am going to disconnect it and fill it to the spec pressure.. Will report back!

Wish me luck! :)

 

[AK_NC]

Expansion tanks are typically pressurized to match your incoming pressure. Before putting a bicycle pump on the Schrader valve put a pressure gauge on your hose bibs. Good house hold pressure is 50-70 psi. Pump up you expansion tank to match what your hose bibs says. Also, expansion tanks go bad. If there's water on the air side of that tank the rubber bladder has failed and it's time for a new one.
As for the frequency of the vibrations, I would look at your pipe hangers, both vertical and horizontal. If you see loose ones hammer them back in, or consider adding hangers, you can have too few, but you can't have too many.

 

[Electron Spin]

AK_NC

I like your hanger philosophy. :)
I do not know what the house input pressure is. Would it be located outside where they read the usage?
Anyway, it flows just about like any regular house, good nuff for a spray nozzle to wash a car.

So this is what I did. I went and bought a low-pressure gauge. The tank air pressure was at or near zero so I went and bought a bicycle pump and pumped it up to mgf specification of 5-7 lbs after draining the tank well and running a bladder pressure test. Hooked it all back up and am now in hour 2 of the fill-up. I opened the output and it squirted real good w/ some expected air pops/bubbles.

I bought this hunk of junk used abt 15 years ago from a friend that needed the money. The bottom of the tank is rusted and the poor bladder probably looks like a dead tire on the side of a highway.

Anyway, fella's I really appreciate all the ideas and input.

Will make a final transmission tomorrow!

Thanks again,
Alex

 

[Asymptotic]

1. What are the characteristics of filter #1 and #2?
I'm envisioning #1 is sized to act as a pre-filter (in the 10 to 50 micron range, depending on incoming water quality), and #2 in the 1 to 5 micron range, possibly with activated carbon to serve as a polish filter. Are they string-wound elements, or melt blown polypropylene or polyethylene cartridges?

2. What is the media in the 3 port 'main filter'?
I've seen standard filter bodies equipped with a waste port for back-flushing the media to increase its service life, but the existence of filter #1 and how the 'main filter' is plumbed into the 'switch' has me thinking it may be a reverse osmosis stage.

3. Can you position a graduated 3 or 5 gallon bucket under the spigot? With that, and a stopwatch (or wristwatch with seconds resolution) you can measure flow rate (GPM). I'm wondering if the thumping symptom commences shortly after the 2-1/2 gallon expansion tank has emptied.

Hooked it all back up and am now in hour 2 of the fill-up

I'm thinking out loud here, but the flow capacity of an RO element probably isn't very high (tenths of a GPM, perhaps), and the filter system manufacturer would have had to design the 'switch' to bypass the 'main filter' during heavy demand periods where the expansion tank had emptied. I'm wondering, could the thumping symptom be caused by whatever valve logic exists in the 'switch' in combination with an underinflated expansion tank bladder?

 

[Electron Spin]

1. What are the characteristics of filter #1 and #2?
I'm envisioning #1 is sized to act as a pre-filter (in the 10 to 50 micron range, depending on incoming water quality), and #2 in the 1 to 5 micron range, possibly with activated carbon to serve as a polish filter. Are they string-wound elements, or melt blown polypropylene or polyethylene cartridges?

2. What is the media in the 3 port 'main filter'?
I've seen standard filter bodies equipped with a waste port for back-flushing the media to increase its service life, but the existence of filter #1 and how the 'main filter' is plumbed into the 'switch' has me thinking it may be a reverse osmosis stage.

3. Can you position a graduated 3 or 5 gallon bucket under the spigot? With that, and a stopwatch (or wristwatch with seconds resolution) you can measure flow rate (GPM). I'm wondering if the thumping symptom commences shortly after the 2-1/2 gallon expansion tank has emptied.
I'm thinking out loud here, but the flow capacity of an RO element probably isn't very high (tenths of a GPM, perhaps), and the filter system manufacturer would have had to design the 'switch' to bypass the 'main filter' during heavy demand periods where the expansion tank had emptied. I'm wondering, could the thumping symptom be caused by whatever valve logic exists in the 'switch' in combination with an underinflated expansion tank bladder?

Those are really good questions for the manufacturer to be sure concerning permeability functions and filter sizes. Looks like my #1 problem stopped with evacuating the tank and pressurizing the bottom side of the bladder to 7.5 PSI.

Tomorrow I am going to call the manufacturer for some technical details and life expectancy.

Look fella's, thanks again for all your help and thinking out loud. Ya can't beat teamwork.

Also, sorry to Greg if I posted this inquiry in the wrong section. You're dealing with a half-baked retired RF EE and physics instructor here. :)

Regards,
Alex

 

[Tom.G]

Hi Alex (@Electron Spin ),
Maybe you can help out on this thread. https://www.physicsforums.com/threads/alternatives-to-creeping-contacts-for-high-frequencies.960914/

Cheers,
Tom

 

[Electron Spin]

SITRIP:

Well, Problem fixed.
Yes, I know I posted "problem fixed" in post # 9 but now repeatability has been verified to be a-ok and nothing blew up to take half the county with it...

I called the mfg. told indicated the make and model, the guy asked me in so many words what was it like back in the Mesoproterozoic days.
I told him I didn't know Fred too well but Barney and I were chums..

Sooo, I did everything in post #9 and shortened the tubes to non-resonant lengths related to the resonant freq of the thumping. =< J/K. (That's how us RF guys think, I guess. Never can be too careful).

Thanks again peeps.

73,
Alex