Hot water recirculation pump orientation

[wwhitney]

You'd install a tee in the water feed just upstream of the valve manifold, then a short riser to a water hammer arrestor.

Depending on the physics of water hammer, a different arrangement might be more effective. E.g. putting in a jog up and then back down on the horizontal water supply line (what you'd get with (4) 90's), and then changing the upper downstream 90 into a tee with a short vertical riser for a water hammer arrestor. That way the pressure wave would be directed at the water hammer arrestor, and only passes upstream through the tee side branch and the two upstream 90s.

Worth checking out, it should be a known thing.

Cheers, Wayne

 

[Phog]

An expansion tank at the water heater can't help until the pressure wave travels from the irrigation valves all the way to the water heater.

This isn't the right way to think about it. There would not be a large pressure wave that travels through the house plumbing. There will instead be a momentary high flow. The expansion tank would allow the flow in as the momentum from the shut-off irrigation water pushes water into house plumbing, the pressure will be damped as the tank absorbs the water, and then the water will flow back out as pressure equalizes. You are right that there will be a pressure differential between the irrigation shutoff valve and the expansion tank (flow is impossible without pressure differential), but it will be extremely low due to the relatively large diameter of the pipes in comparison to the small amount of flow.

But you want something to protect the irrigation pipes from the water hammer.

The irrigation pipes will be downstream of the irrigation shutoff valve & not see any water hammer.. unless I'm missing something? I can be dense sometimes

 

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[Niccolo]

To recap where we're at...

An expansion tank is worth considering as an insurance policy in case my utility installs a check valve on the main supply later.

A check valve that prevents irrigation water from contaminating potable water is a must-do, and should be located where irrigation water branches off the main water supply.

A water hammer arrestor should be located as close to the irrigation system as possible, because then it will protect the upstream PVC irrigation pipes, too. I didn't follow all of the suggestions about piping the water hammer arrestor, though.

 

[Phog]

An expansion tank is worth considering as an insurance policy in case my utility installs a check valve on the main supply later.

It should also solve the water hammer problem -- see my above post.

A check valve that prevents irrigation water from contaminating potable water is a must-do, and should be located where irrigation water branches off the main water supply.

This depends on if your irrigation system is uphill from your house plumbing. If not the the check valve will not be needed to protect your house as there is no way head pressure could push water into your house plumbing (water only flows downhill). But i think you can plan on someday -- whether it's a year from now or 25 years from now -- your utility will install one at your service connection. It protects their mains from contamination, and seems to be the way the world is going.

A water hammer arrestor should be located as close to the irrigation system as possible, because then it will protect the upstream PVC irrigation pipes, too. I didn't follow all of the suggestions about piping the water hammer arrestor, though.

The irrigation system won't see water hammer because it's downstream of the shutoff. Water hammer only occurs upstream of a quickly shut valve.

 

[Reach4]

The irrigation system won't see water hammer because it's downstream of the shutoff. Water hammer only occurs upstream of a quickly shut valve.

The irrigation system has valves that are the culprits. There is irrigation plumbing upstream of those valves.

 

[Phog]

The irrigation system has valves that are the culprits. There is irrigation plumbing upstream of those valves.

Ahh I see - we're talking about several branches each with individual shutoffs. Sorry I missed that. Either way, a water hammer arrestor or an expansion tank downstream would mitigate hammer throughout the system.

 

[Niccolo]

My property is level, no uphill or downhill, though I'm not sure how critical that is anyway.

My gut was that having a check valve where the irrigation water leaves the main water supply was necessary, because there are scenarios where irrigation system water could get pulled into the potable water supply, right? There's already a shutoff valve there, are there combined check valve/shutoff valves, e.g. devices that only allow flow in one direction and allow that flow to be manually turned on and off?

It sounds like some people think a water hammer arrestor, as close to the irrigation system that's triggering the water hammer as possible, is desirable. Others are suggesting that it might not be necessary because an expansion tank on the cold water supply to my water heater would take care of the excess pressure.

 

[Phog]

My gut was that having a check valve where the irrigation water leaves the main water supply was necessary, because there are scenarios where irrigation system water could get pulled into the potable water supply, right?

This can only possibly occur if either of the following is true. 1) Some of the irrigation plumbing is elevated above the level of your house (like if you live on a hill side). 2) There is a vacuum created inside your house plumbing that sucks water up from the irrigation plumbing that is at/below the house elevation level. Scenario #1 is eliminated since you have a flat yard. Scenario #2 would be very difficult to imagine -- the only way I can see it occurring is if you have your water heater full of trapped air and there is a temperature change toward the cold, which would cause the trapped air to contract and create a suction. I suppose that could occur, in theory.

 

[Terry]

Irrigation uses either a vacuum breaker or a reduced pressure back flow preventer.
The vacuum breaker can be used if it's higher than all of the irrigation. If not, then the reduced pressure back flow is used.
It is a very big concern that your water is not contaminated by an outside source. It's why there is an air break on all faucets and anti-siphon on hosebibs.

 

[Niccolo]

So my water utility took my call very seriously. They sent out a few guys, so I had a chance to chat with them.

There are two PRVs that reduce pressure in the water supply, one at the top of a nearby hill and a second one at a nearby street. The second one is needed because the water traveling down the hill builds pressure.

There are not currently check valves at individual homes. Upgrades to water infrastructure are likely in the near term, in part because a recycled water project is coming online for gray water for irrigation. As part of that, a requirement that homeowners have check valves/backflow preventers installed seems likely.

 

[Niccolo]

Irrigation uses either a vacuum breaker or a reduced pressure back flow preventer.
The vacuum breaker can be used if it's higher than all of the irrigation. If not, then the reduced pressure back flow is used.
It is a very big concern that your water is not contaminated by an outside source. It's why there is an air break on all faucets and anti-siphon on hosebibs.

Okay, so my irrigation needs some kind of backflow preventer located where the irrigation line leaves the main water line. That could be either a vacuum breaker (if it's higher than my irrigation--how much higher?) or a reduced pressure backflow preventer.

That deals with potential backflow scenarios, but does it also deal with the water hammer issue? I'm guessing not, and I'd still want a water hammer arrestor located near the irrigation system valves are are generating the pressure shock.

It seems I've woken a sleeping dragon, and my water utility is now mandating that I either install a double check valve just after my water meter or sever my irrigation system from their supply.

 

[Reach4]

The deals with potential backflow scenarios, but does it also deal with the water hammer issue? I'm guessing not, and I'd still want a water hammer arrestor located near the irrigation system valves are are generating the pressure shock.

How many valves are there? Are they together or distributed around?

It seems I've woken a sleeping dragon, and my water utility is now mandating that I either install a double check valve or sever my irrigation system from their supply.

Go with it.

 

[Terry]

It seems I've woken a sleeping dragon, and my water utility is now mandating that I either install a double check valve just after my water meter or sever my irrigation system from their supply.

It is what needs to happen. Just git er done!

 

[Phog]

That deals with potential backflow scenarios, but does it also deal with the water hammer issue? I'm guessing not, and I'd still want a water hammer arrestor located near the irrigation system valves are are generating the pressure shock.

I will leave the irrigation check valve vs. vacuum breaker discussion to others. However I stand by the assertion that a thermal expansion tank located at & appropriately sized for your water heater will also have the side effect of arresting this water hammer from your irrigation system. Since your municipality is apparently going to be requiring a double check valve anyway then why not just install it + add a thermal expansion tank now? And be done with it all? This way you don't need a hammer arrestor.

 

[Niccolo]

Okay, to recap...

Utility will force me to install a double check valve (a type of backflow preventer) just downstream of my meter, presumably they will have specifications that need to meet.

My irrigation needs some kind of backflow preventer located where the irrigation line leaves the main water line. That could be either a vacuum breaker (if it's higher than my irrigation--how much higher?) or a reduced pressure backflow preventer.

I'm guessing the electrically-controlled irrigation valves, which are located all together, need a water hammer arrestor located as close to them upstream as possible. But maybe that unnecessary if I have an expansion tank (which I need to have anyway).

And with a backflow preventer installed, my water heater will need an expansion tank at the cold water supply.

The wrinkle here is that plans are apparently afoot to supply recycled gray water in the coming year, and if I can tap into that as a homeowner, I might want to hold off on a bunch of expensive plumbing work. One option is to temporarily sever the connection from my main water supply to irrigation and to hand water in the backyard as needed for a few months.

 

[wwhitney]

I will leave the irrigation check valve vs. vacuum breaker discussion to others. However I stand by the assertion that a thermal expansion tank located at & appropriately sized for your water heater will also have the side effect of arresting this water hammer from your irrigation system. Since your municipality is apparently going to be requiring a double check valve anyway then why not just install it + add a thermal expansion tank now? And be done with it all? This way you don't need a hammer arrestor.

That would be a good experiment to do, because my understanding is that neither of those will affect the pressure spike reading the OP gets at the outdoor hose bibb, since that measurement location is between the irrigation valves and the expansion tank. If you're right, the OP is done; if I'm right, he can go ahead and install a water hammer arrestor by the irrigation valves.

Water hammer is different from thermal expansion, because the latter is comparatively slow (the water temperature rises comparatively slowly), so the whole system can be considered to be in equilibrium at every point in time (just a slowly changing equilibrium). 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.

Cheers, Wayne

 

[wwhitney]

Utility will force me to install a double check valve (a type of backflow preventer) just downstream of my meter, presumably they will have specifications that need to meet.

So basically they are saying "Oh, you have irrigation, we don't trust you to implement it correctly, we want to protect our water main from contaminants, and we want the protection right after the meter so we can see it." Seems a bit draconian, and expensive if your setup is like mine: a small meter box in the public sidewalk that would probably require enlarging to fit in a double check valve.

My irrigation needs some kind of backflow preventer located where the irrigation line leaves the main water line. That could be either a vacuum breaker (if it's higher than my irrigation--how much higher?) or a reduced pressure backflow preventer.

It doesn't have to be where the irrigation line leaves the main water line. It does need to be upstream of all irrigation outlets (and should be upstream of any lower quality buried pipe like some irrigation systems use). But common irrigation valves have a vacuum breaker built-in, post a picture of yours and we can tell you.

The wrinkle here is that plans are apparently afoot to supply recycled gray water in the coming year, and if I can tap into that as a homeowner, I might want to hold off on a bunch of expensive plumbing work. One option is to temporarily sever the connection from my main water supply to irrigation and to hand water in the backyard as needed for a few months.

Maybe the water utility would accept an air gap: you could install a spigot that fill a big gravity tank, and then install a pump to feed your irrigation system. Just a possible option.

Cheers, Wayne

 

[Niccolo]

Three pictures attached:

1) Main water in with junction supplying backyard irrigation

2) Backyard irrigation valves, frontal

3) Backyard irrigation valves, top view

 

[Reach4]

Maybe the water utility would accept an air gap: you could install a spigot that fill a big gravity tank, and then install a pump to feed your irrigation system. Just a possible option.

A (big tank and a cistern and a pump) vs a backflow preventer? A back flow preventer is not a big deal.

So just two valves with the inputs close together? Sounds easier than what I was suspecting. A big water hammer arrestor at the input of those valves should help a lot. I don't have one to suggest.

 

[wwhitney]

A (big tank and a cistern and a pump) vs a backflow preventer? A back flow preventer is not a big deal.

Unless that backflow preventer has to be in the utility water meter box and the utility wants several thousand dollars for the permitting and work in the right of way to enlarge the box, etc.

Cheers, Wayne