Hot water recirculation pump orientation

[wwhitney]

Three pictures attached:
3) Backyard irrigation valves, top view

Yeah, so the big cylinder part in the front of the valve is the atmospheric vacuum breaker. That has to be at least 6" above the highest sprinkler outlet downstream of it. So if it's 12" off the ground (for example), as long as your yard doesn't rise more than 6" to a sprinkler head, that's fine. Visually flat may not actually be flat, so if it's a big yard, it could matter.

Cheers, Wayne

 

[Niccolo]

False alarm. The utility cross-contamination specialist was just here. His guys told him I was seeing sustained super-high pressures and that they thought I had a booster pump (apparently people with huge backyard irrigation setups can experience a loss of pressure and install booster pumps to mitigate it). I don't have a booster pump. He was amused at the misunderstanding. He said the atmospheric vacuum breaker integrated into my irrigation system was sufficient to prevent backflow contamination into the potable water line, so he didn't suggest any changes were necessary (I was a bit surprised he didn't ask me to install a backflow preventer where the irrigation line leaves the main water line). Also, I will not be able to tap into the grey water for my irrigation, so that's off the table.

But I still have the irrigation system water hammer issue. So...

Install an expansion tank at the cold water input to my hot water heater and be done with it? This has the upside that if check valves are required for each house later, I already have an expansion tank, but it doesn't sound like that's in the works. It also provides whole-house protection if for some reason I ever experienced high pressure.

Install a water hammer arrestor just upstream of the irrigation system? This directly targets the issue I'm having, but doesn't provide whole house protection or cover the potential future contingency of check valves being required. If I go this route, is the momentary PSI I'm reporting of 120-180 high enough that you'd shut off the irrigation system until this got addressed?

 

[Sponsor]

 

[Phog]

Whereas a fast closing solenoid valve is a purely dynamic phenomenon, the sudden interruption of flowing water, generating a pressure wave that travels in all directions as the speed of sound in water.

Good discussion & fun to talk about this kind of stuff while my day job is paused. What you are describing here is a sonic boom, which requires a supersonic shockwave initiator. To have this occur would require the water velocity at some point during the valve closing process to be higher than the speed of sound (like the crack of a whip). I don't believe this is even a remote possibility at the static pressures we are talking about here, but I haven't done a calculation to 100% confirm.

Also the valve does not close instantaneously, it does take some finite amount of time, say 1/2 second. So there is at least some time for flow into a downstream expansion tank, even remotely located after some length of pipe, and take up the water being pushed into the system by the incoming momentum.

 

[Phog]

But I still have the irrigation system water hammer issue. So...

You will get rid of most, but maybe not all, of the hammer with a water heater expansion tank. The TET will take care of absorbing the momentum of the water from the street mains to the inlet of your house. What little hammer that will be remaining after installing the TET will be only in the further length of pipe between the house/irrigation split-off point & the irrigation valves themselves.

But how much of an issue is that hammer, really? Maybe someone else can correct me here but I have not heard that water hammer is damaging to well-secured / non-movable pipes. I've only heard of fittings sometimes cracking when a loose unsecured pipe length can wiggle back and forth, a lot, over a long period of time.

To me it seems like you really only need to protect your hot water tank from pressure flexing to prevent premature failure. Just my opinion though.

 

[wwhitney]

Good discussion & fun to talk about this kind of stuff while my day job is paused. What you are describing here is a sonic boom, which requires a supersonic shockwave initiator. To have this occur would require the water velocity at some point during the valve closing process to be higher than the speed of sound (like the crack of a whip). I don't believe this is even a remote possibility at the static pressures we are talking about here, but I haven't done a calculation to 100% confirm.

From the second google hit for me for "water hammer sonic boom":

https://plumbingperspective.com/water-hammer-annoying-to-destructive-in-50-70-psi

Now, I have no idea if that's a reputable source or not, nor have I done the research to see if that's really correct. But at least some people seem to think that water hammer is a sonic boom. Pretty sure solenoid valves can close a lot faster than 1/2 second.

Also, it seems to me that under your model, the OP would never see +80 psi spikes at the entrance hose spigot. He's got no check valve, so the entire water main volume is there to absorb expansion.

If you do some proper research to determine which one of is correct, please let us know. I'm apparently only motivated to do a single google search and then let my confirmation bias kick in.

Cheers, Wayne

 

[Phog]

Very interesting, however I'm still skeptical. The speed of sound in water is several multiples of its speed in air, and intuitively I don't see why it's necessary to have a supersonic component. The momentum of the water mass in the incoming pipe will create a pressure spike (it will apply a force) as it comes to a stop and it could easily be on the order of 80psi -- especially if there is a long length of pipe from the street water main to the house, lots of mass in motion there. The house plumbing will do nothing to buffer this since water is incompressible under almost any practical conditions. (However if there is an expansion tank in the house it WILL buffer the spike, just like I've been saying ). I'm also too lazy to research the topic very much, but a quick Google search also turned up this: https://www.ianj.com/Velocity-of-Flow-and-Water-Hammer

 

[Niccolo]

There seems to be an overwhelming consensus that water hammer is damaging. I'm not seeing much to suggest this is a controversy or many people think it's not damaging.

If we assume it's damaging, then I'm left with the question of whether a water hammer arrestor or expansion tank seems like the more appropriate solution in my case. The former would be located right where the shock wave is generated, to nip it in the bud. The latter would be maybe 50 feet away, inside the garage by the water heater, but maybe that's not critical and it would still do a good job mitigating the shock.

 

[Phog]

If your utility is telling you that you need a thermal expansion tank at the water heater soon regardless, you could install that first and then take a measurement to see how much reduced the pressure spikes are by it. Then proceed to put a hammer arrestor near the irrigation valves at a later date -- if needed.

 

[wwhitney]

And if you take that approach, please tell us if the expansion tank reduces the pressure spikes!

BTW, on the OP, you should reverse the circulating pump. : - )

Thanks,
Wayne

 

[wwhitney]

OK I'd like to reference wikipedia, on the basis that if they got it wrong, someone would have fixed it by now:

https://en.wikipedia.org/wiki/Water_hammer

Cheers, Wayne

 

[Phog]

The case that applies to the present situation is described in that Wikipedia article under the section titled "Slow valve closure; incompressible fluid" (notice that it contains the same equation that is referenced in the article linked to a few posts back, post # 126).

 

[Niccolo]

And if you take that approach, please tell us if the expansion tank reduces the pressure spikes!

BTW, on the OP, you should reverse the circulating pump. : - )

Thanks,
Wayne

Yep, circulation pump reversed, albeit still broken and awaiting warranty replacement because the local plumbing supply house and Grundfos need to get their ducks in order...

 

[Niccolo]

Hmm, interesting new wrinkle.

I was working this morning and noticed the nearby shower suddenly started dripping meaningfully, which it's never done before. All components are only about 1.5 years old, but we do have very hard water. Anyway, I checked the PSI gauge on my outside hose spigot, and instead of the usual 53-58 PSI, it was at a steady 108 PSI. I went and checked the water heater, and it was off, so I turned up the temperature to get it to come on, and five minutes later the gauge was at 114 PSI. I then ran the kitchen hot water tap for several minutes, but to my surprise, that only dropped the pressure to 110 PSI (running cold water also doesn't seem to drop the pressure much, I would have thought opening taps would dramatically vent pressure?).

My home does not have any sort of backflow preventer at the water supply. The nearest utility PRV is a few blocks and slightly uphill away, for the neighborhood, and is apparently set to output at 30 PSI. My usual pressure is consistently 53-58 PSI.

We previously established that my irrigation system was causing water hammer when it kicked in early morning and that's what was leading to the tattletale hand showing huge spikes overnight. But this is different; assuming my PSI gauge hasn't suddenly gone bad, after a week of monitoring with constant results, today my steady-state PSI is doubled. Any words of wisdom for diagnosing what might be going on here, e.g. utility water pressure being higher for some reason, or my water heater raising the pressure and for some reason it's not dissipating into the utility lines, or otherwise?

Shower keeps dripping.

EDIT: I do recall past circumstances where the shower suddenly dripped for a little while and then it stopped again, so I bet you I've occasionally experienced high pressures like this. But I'm mystified about the source. The utility seems to take delivery pressure extremely seriously, it seems bizarre if their delivery pressure doubled like this. And given the lack of a backflow preventer for my house, how could I be generating these kinds of pressures in my house and not dissipating them into the utility supply lines?

EDIT 2: Pressure at 120 PSI now. Sink faucet flow when hot or cold are fully open seems more vigorous, not surprisingly. Shower still dripping, obviously. Anything I can do in the short-term to reduce the pressure (while I figure out long-term solutions)?

 

[Jadnashua]

As you heat the water, if no taps are open and there are no leaks, the initial expansion balloons any flexible pipes (like say those to your washing machine if you leave the valves open, and any faucet or toilet supply), then when they reach their limit, you're trying to balloon metal, and the pressure will quickly spike from there. Without a check valve, that expansion just pushes back out into the supply where there will be some capacity to absorb it. The total volume of expansion depends on the temperature the water starts at and how much water is being heated, and the delta in temperature. Without using hot water, raising the aquastat on the WH slightly to cause it to come on, the delta isn't much, therefore, the increased volume will be small. From cold to normal WH temps, in say a 40g tank, you might see a couple of cups. In a closed system, that's easily enough to reach over 150psi, where the WH T&P safety valve can open to relieve it. WHere I live, in a cold snap, mu delta-T exceeds 100-degrees (incoming is very close to freezing, and my tank is set to 140-degrees).

To properly size an ET, you need your worst case incoming water temperature, the size of the WH, and what you've got the WH set to produce that generates the delta T. The calculators on the ET manufacturer's website will then tell you the size tank you need. Do not go smaller, but larger doesn't hurt (except the bigger ones cost a little more).

Your PVC irrigation piping doesn't like those pressure spikes, either, so you would want to protect them with a hammer arrestor. The strength of some pvc piping degrades if it is exposed to UV light, so it is more susceptible to fracturing, so helping to relieve stresses from water hammer are prudent. Generally, you want that as close to the offending valve as possible for optimum results. An ET for your WH will be further away, but still would help.

In some places, when an irrigation system is connected, they not only want a special check valve, but annual certification from a licensed inspector to verify that it is working properly. Having that protects not only your house, but the entire community near you. A simple check valve certainly helps, but isn't as good as one designed for irrigation.

So, I'd install an ET, see what that does for you on spikes, and then seriously consider adding a hammer arrestor on the supply side to your irrigation control valve(s). WHen you stop the flow rapidly, it's like the water hitting a brick wall and it bounces back from that. With a hammer arrestor, it compresses some air in a chamber. You want an engineered one, not a home-made one that's just a air column, as the air in one will be absorbed after a few months.

Don't know what part of IN you are in, but with the water supply coming above ground before going into the house wouldn't be allowed around where I live...it would freeze overnight. When the water is moving, that isn't likely to happen, but overnight, or say when nobody is home during the day, that water is just sitting there, and the exposed piping would just freeze and split around here.

 

[Niccolo]

Really appreciate all the input.

If we assume that my utility-provided water pressure is constant, and knowing that there is no backflow preventer installed so pressure should significant dissipate into the supply lines, isn't it surprising that my water heater is able to raise the pressure from the steady-state 53-58 PSI all last week to 110-120 PSI now?

And when I run the hot and cold water at a tap for several minutes, shouldn't that dramatically reduce the pressure, assuming again it's not coming from the utility supply line?

I'm confused about what could be different today versus all of last week. Obviously one option is utility supply pressure, e.g. maybe a mechanical failure of one of their PRVs for the neighborhood. But if it's not that, it seems odd, no?

Also, I'm on the Central Coast of California, so frost is exceedingly rare.

To clarify where I'm at:

- I'm absolutely installing a water hammer arrestor as close as possible to the irrigation valves, sometime in the next week or two

- I had decided to wait on an expansion tank, since my water pressure was constant all last week at 53-58 (aside from irrigation water hammer), but all of a sudden today this high constant pressure has thrown a wrench into that.

EDIT: Constant pressure peaked at 124 PSI but is down back to a normal 55 PSI. I have no idea what released so much pressure, there's been minimal hot or cold water use. EDIT2: Actually, I have a house guest who did take a shower, so that almost certainly explains the return to normal pressure. Apparently the shower pressure was unpleasantly high (not very surprisingly).

 

[Reach4]

And when I run the hot and cold water at a tap for several minutes, shouldn't that dramatically reduce the pressure, assuming again it's not coming from the utility supply line?

Compared to running the tap for 1 or 2 seconds at the same rate? No. Compared to no-flow conditions? Maybe.

 

[Bannerman]

Pressure at 120 PSI now. Sink faucet flow when hot or cold are fully open seems more vigorous, not surprisingly.

As the pressure is not dropping when running water, and as you have no pump to boost pressure, you may now wish to involve your municipal water supplier as their PRV may be experiencing an intermittent lagging issue thereby not reacting rapidly enough to maintain the usual 55-60 psi downstream pressure.

Since the sudden closing of the irrigation solenoid valves is causing the water hammer on the feed line, suggest locating an expansion tank on the feed line to the solenoid valves. The cusion of air within the expansion tank will be more prone to absorb the water hammer before it has opportunity to travel through the bulk of house plumbing to an expansion tank farther away.

The downstream side of the solenoid valves do not benefit from expansion tanks as the flow is stopped at each solenoid valve so any remaining downstream pressure in those lines will be casually relieved through the always open sprinkler heads.

Locating an expansion tank on the irrigation feed line will also address a pressure increase caused by heating water in the water heater. With a check valve on the line leading from the municipal supply, when the water in your WH expands, it will increase pressure equally in both the cold and hot water lines throughout your home. Regardless of where the expansion tank is located, the expansion tank will provide a place to absorb the expansion.

A contradiction to this is with later installing a water softener. When the softener location results in a short pipe distance between it and the water heater, then a check valve is often installed after the softener to prevent the possibility of hot water from expanding back into the softener. With a check valve after the softener, then an expansion tank would be needed downstream of the CV even if one exists upstream.

 

[Niccolo]

As the pressure is not dropping when running water, and as you have no pump to boost pressure, you may now wish to involve your municipal water supplier as their PRV may be experiencing an intermittent lagging issue thereby not reacting rapidly enough to maintain the usual 55-60 psi downstream pressure.

Since the sudden closing of the irrigation solenoid valves is causing the water hammer on the feed line, suggest locating an expansion tank on the feed line to the solenoid valves. The cusion of air within the expansion tank will be more prone to absorb the water hammer before it has opportunity to travel through the bulk of house plumbing to an expansion tank farther away.

The downstream side of the solenoid valves do not benefit from expansion tanks as the flow is stopped at each solenoid valve so any remaining downstream pressure in those lines will be casually relieved through the always open sprinkler heads.

Locating an expansion tank on the irrigation feed line will also address a pressure increase caused by heating water in the water heater. With a check valve on the line leading from the municipal supply, when the water in your WH expands, it will increase pressure equally in both the cold and hot water lines throughout your home. Regardless of where the expansion tank is located, the expansion tank will provide a place to absorb the expansion.

A contradiction to this is with later installing a water softener. When the softener location results in a short pipe distance between it and the water heater, then a check valve is often installed after the softener to prevent the possibility of hot water from expanding back into the softener. With a check valve after the softener, then an expansion tank would be needed downstream of the CV even if one exists upstream.

Yep, it's definitely possible my utility supply is the culprit, though it would suggest a pretty serious failure in their systems.

My thought was water hammer arrestor (i.e. mini-expansion tank) on the irrigation supply line, close to the irrigation valves, and likely also expansion tank, but in the classic location at the water heater cold water supply line. Full-sized expansion tank on the irrigation supply line seems like a pretty unusual prescription.

There is no check valve on the utility supply, at least not prior to the neighborhood PRV.

A water softener is probably in the cards sometime soon, too, so that's an interesting additional wrinkle to consider.

 

[Bannerman]

Full-sized expansion tank on the irrigation supply line seems like a pretty unusual prescription.

Not sure what you mean by Full-sized. A thermal expansion tank by its very nature, will usually be quite small for a residential application, maybe 2-3 gallons actual fluid capacity.

Because water cannot be compressed, even a small amount of expansion will result in excessively high system pressure when there is nowhere for that expansion to be absorbed. When there is no X-tank, the water heater pressure relief valve will usually begin to seep when there is nowhere else for pressure to be relieved.

An expansion tank utilizes a sealed chamber of compressed air at the same pressure as the water chamber. Since air can be further compressed, the tank provides space to absorb the thermal expansion of the water. The air also can act as a shock absorber to absorb sudden energy. When a substantial volume of water flowing at high velocity is suddenly stopped such as through a solenoid controlled valve, that will be similar to a vehicle traveling at 60 mph, and then immediately dropping to 0 mph when slamming into a large tree.

Although there is no back-flow prevention device currently located between your home and the municipal supply, best to anticipate one will be added even if your home is disqualified from participation in the grey water irrigation program.

https://www.amtrol.com/resources-rewards/selection-tools/

 

[Niccolo]

Not sure what you mean by Full-sized. A thermal expansion tank by its very nature, will usually be quite small for a residential application, maybe 2-3 gallons actual fluid capacity.

Because water cannot be compressed, even a small amount of expansion will result in excessively high system pressure when there is nowhere for that expansion to be absorbed. When there is no X-tank, the water heater pressure relief valve will usually begin to seep when there is nowhere else for pressure to be relieved.

An expansion tank utilizes a sealed chamber of compressed air at the same pressure as the water chamber. Since air can be further compressed, the tank provides space to absorb the thermal expansion of the water. The air also can act as a shock absorber to absorb sudden energy. When a substantial volume of water flowing at high velocity is suddenly stopped such as through a solenoid controlled valve, that will be similar to a vehicle traveling at 60 mph, and then immediately dropping to 0 mph when slamming into a large tree.

Although there is no back-flow prevention device currently located between your home and the municipal supply, best to anticipate one will be added even if your home is disqualified from participation in the grey water irrigation program.

https://www.amtrol.com/resources-rewards/selection-tools/

I'm making a distinction between a water hammer arrestor (which is like a tiny expansion tank) and an actual expansion tank (which I was calling a full-size expansion tank).

It was my impression that a water hammer arrestor should be located on the irrigation supply line, as close to the irrigation valves as possible, which will likely be sufficient to deal with the transient high pressures I was seeing (water hammer). If I understood you correctly, you were suggesting substituting an expansion tank for the water hammer arrestor on the irrigation supply line, and that suggestion is what I was calling unusual.

The sustained high pressures I saw this morning, on the other hand, likely call for an expansion tank and/or a PRV at the house water supply, depending on their source (which I am trying to diagnose, including with help from this forum).

Hope I've been more clear here, sorry for any confusion I may have caused.