Undersink water filter question

[Mike from Brier]

Hey all you plumbing pro's:

I have an approximately 4 year old 2 stage undersink OmniFilter with its own faucet on the sink ledge. Ever since I installed it, per manufacturers instructions, it has dripped from the filter faucet about 5 minutes after someone takes a hot shower or does a sink full of dishes using the hot water. I get it to stop dripping only after opening a cold water faucet (anywhere in the house). Most of the time it will start back up in a couple minutes, so I must repeat this process two or three more times before it stops.

I assume this is due to a pressure rise in the supply side of the filter due to some kind of thermal expansion, but what I don't understand is why this faucet valve can't handle the rise. It's the second valve, and both have done this. Omni replaced the first one under warranty thinking it was defective. Now I'm not so sure.

My ambient water pressure coming into the house is around 40-45 psi as supplied by the water district, and measured at a hose bib outside. All plumbing leading to this sink on the main floor is new copper in an exposed but heated basement. The supply to the sink is 1/2", and the supply from that to the filter is 1/8 or 3/16" plastic tubing, whatever came with the kit.

What's really going on here, and what pressure would do you think this filter faucet should be able to handle? Should I get some kind of gauge to measure the pressure at the kitchen sink faucet when the filter faucet starts dripping? Has anyone ever found it necessary to install some kind of pressure reducer/relief in the supply side of a filter such as this?

I'm really stumped so would appreciate any feedback and ideas.

Thanks!

 

[GoTanklessToday]

Do you have a properly sized and installed thermal expanaion tank on your water heater?

 

[Sponsor]

 

[Mike from Brier]

Nope. I guess I should go read some of the threads in this forum about thermal expansion tanks and their uses. Admittedly, I know nothing about them, as I've never had any experience with them. But before I do, what would make one important in this application when the lack of one under similar conditions in my previous homes didn't seem to have any adverse effects? I mean, all systems being similar (I realize none can be "equal"), why would one react this way when the others don't? I don't get the concept.

I've had two other homes that I've installed these undersink units in, and neither of them had a water heater with a thermal expansion tank. And neither of them had this problem. I've lived in probably a dozen other places over the years, and none of them had thermal expansion tanks, either, and not one of them ever developed any kind of known "expansion" issue; i.e.: no drippy faucets after the hot water has been running. By the way, I've always lived in the Pacific Northwest. The weather, average barometric pressure, and humidity just doesn't change much around here throughout the year. Don't know if this makes a difference or not, but I thought I'd toss it in for giggles.

How many pounds can thermal expansion raise a 40-50 PSI static pressure system by, anyway? Could I expect to see it raise by as much as 40 to 50 more at the faucet?

And, is the lack of an expansion tank the most probable cause of my original issue? If so, why? (I know.........go back and read those threads you mentioned earlier, dummy! )

More feedback, please! Mike

 

[GoTanklessToday]

Thermal expansion can take a 50 lb static pressure up to 150 in short order. It should never exceed 150, because your water heater's T&P will blow at that pressure. What you have is classic thermal expansion in action. When you heat water it expands. Since you cannot compress liquid, it need somewhere to go. It's just like the radiator recovery bottle under the hood of your car. When the engine block heats up, the coolant and water mixture expands to the point where the block and radiator can't contain it all. It send the "extra" water to the bottle, and then when things cool back down, it syphons itself back into the radiator.

In your case, Why its causing the filter to drip is beyond me. As for why other homes didn't require the exp tank, I get that question all the time. The answer is mainly because the other homes probably didn't have a closed system. Different areas of town will have them, and others won't. For instance, in Edmonds, everyone will likely have a closed system, while homes in south Seattle will most likely not. It depends on your area, or your water pressure. If you had a pressure reducing valve installed, you have a closed system. Some cities have mandated that the water meter have a check valve built in. I'm not sure about Brier. There is a quick check you can do that will tell you if you have a closed system (if you can't see evidence of it, like a PRV, etc). You need a pressure gauge that screws onto a hose bibb or drain valve. Open the valve, and watch the needle on the gauge. Ask someone to run water somewhere in the home (hot or cold, it doesnt matter). Tell them to run it for a few seconds, and then shut it off quickly. If the needle swings back and forth lazily and slowly before coming to a stop, you have an open system. If it's a closed system, the needle will instantly peg. It isn't 100% accurate, but I'd guess 99.

If you have a closed system, you need an exp tank. Whether or not this will stop your filter spout from dripping is unknown. Could there just be a bad lot of those filter valves out there?

 

[Mike from Brier]

Thanks for the detailed explanation! I figured the dripping had to do with expansion, but what I don't understand is, in any given system where there are no crossovers (or leaky mix valves), how can thermal expansion affect the cold water side? Does the expanded hot water "push back" against the supply, therefor raising the water pressure on the cold side somehow? I guess logic dictates that in your closed system, without a PRV or check valve on the supply side, it's probable. Maybe that explains why the "weak link" (filter faucet) shows the symptom. But, I don't have any issues with hot water coming from cold faucets. Is this relevant?

I will do as you suggested and determine whether or not my system is closed, but based on your explanation I suspect it isn't. I'll verify with Brier to determine if the meter has that check valve.

As for a possible bad batch of filter faucets, I can't say for sure, but mine were installed three years apart. It would seem to me Omni would have to have had a long production run of defective valves for this to be the case. And I haven't found anything on the web indicating consumers have been having this problem en masse. If so, I'd think they'd do a recall or something. Their customer service has always been great to me, so I think they have corporate ethics (wait, is that an oxymoron?)...

I've also written Omni to ask what pressure the faucet valve should be able to withstand. Hope to hear from them early next week. And I'll repost when I have the results of my little test re the closed/open system. In the meantime, if you or anyone else has anything to add, I'm all ears!

Thanks again! Mike

 

[GoTanklessToday]

The hot water is the same as the cold water. I mean... all you are doing is taking a leg off the cold main and sending it through a heating device before sending it along it's way. The expansion occurs in the water heater, which is fed by the cold.

 

[Mike from Brier]

Well, the results are in. I rechecked my static water pressure at a bibb, and it is 60 psi. With the gauge installed and tested per the following...

There is a quick check you can do that will tell you if you have a closed system (if you can't see evidence of it, like a PRV, etc). You need a pressure gauge that screws onto a hose bibb or drain valve. Open the valve, and watch the needle on the gauge. Ask someone to run water somewhere in the home (hot or cold, it doesnt matter). Tell them to run it for a few seconds, and then shut it off quickly. If the needle swings back and forth lazily and slowly before coming to a stop, you have an open system. If it's a closed system, the needle will instantly peg. It isn't 100% accurate, but I'd guess 99.

...it didn't swing lazily, but it didn't peg, either. It jumped about 5 psi and settled there. Conclusion? Inconclusive.

After all this exertion, I took a shower (with the gauge still installed). Within a few minutes after the shower, I checked the gauge again and it was sitting around 100 psi. Opening an adjacent valve dropped it to 60 again. Had to do this several times before it settled. Conclusion? Classic thermal expansion.

I heard back from Omni regarding the pressure limits of the faucet and was treated to the following response (cut and pasted):

The unit can withstand up to 100 psi of your water pressure going into the unit. It will lessen while going through the filters & gets restricted slightly by the 1/4" tubing up to the faucet. So if I had to guess....if you had the maximum of 100 psi going into it you probably would get about 90 psi coming out of the faucet.

The hot water should never affect the cold water unless your plumbing is done wrong. Hot water & cold water should be separate to all sources in your home. One should never affect the other.

Thank you for contacting Omnifilter, we appreciate your business.

Fascinating, huh? I do believe their tech support person may very well be a Home Despot (sic) reject. After everything I've read in this forum, I had no idea water pressure acted the way Omni described it!

Also heard from my water department, and the meter servicing my home definitely does not have an integral PRV or regulator. They did say the street pressure in my area was in the neighborhood of 80-120 psi. And since there isn't a PRV inside the home, and the pressure at the bibb is 60 psi, I can only assume there is one between the meter and the house, probably buried in the yard.

Conclusion: I need an expansion tank.

Thanks for all the suggestions and help, everyone. It was truly appreciated!

Mike

 

[Gary Slusser]

Omni was explaining dynamic pressure, when water is being used, not static pressure, when no water is being used. Staic pressure will aways be higher than dynamic pressure due friction losses.

 

[Bob NH]

I assume that you have city water and not a well/pump/tank system.

You need to check that gauge after someone uses a lot of hot water, and then shuts off all water for a while. Check the gauge when the faucet is observed to be leaking.

The water heater is filled with cold water after someone uses the hot water. If it heats for a while and nobody is using any water, hot or cold, the expanding heated water increases the pressure in the system.

The condition exists if you have a pressure regulator because the regulator usually doesn't allow any backflow to the city system (some do).

If you have a problem and need to install an expansion tank, it should be installed at a tee, usually off the cold water line. It shoud be precharged with air at a pressure equal to your normal operating pressure (60 psi).

If you buy such a tank be sure you get one made for city water pressure; NOT the less-expensive kind put on furnaces/boilers. Those are rated for lower pressure and will fail when they are supposed to work.