Backflow preventer in pond/waterfall system

[cmac2012]

One of my client's house is in a nice hilly community, toney but not far from I-280 which goes through some otherwise exclusive property. Their street has a bit of hill action stopping most of the freeway noise but there is a bit of roar nonetheless so they put in a waterfall for some white noies. It's maybe 20 feet long emptying into a 15 foot diameter pond, this in their inclined front yard. It has three little creek/waterfall bits, one goes alongside the sidewalk which descends from the street to the front door.

It's surrounded by bushes and trees, about once a year I need to clean the scum and mud from the gravel and filters, as the flow gets progressively slower. This year I was having a weird problem, it would start to flow after I put it all together and then would go to next to nothing after a minuter or so.

I finally discovered that the backflow preventer just above the pump had failed - the spring mechanism that held the plastic plug had deteriorated, allowing the plug to be pushed up to the top.

There is another backflow preventer at the control panel, which has valves for the flow between the three rivulets to be balanced. Total rise maybe 10 feet.

They want this thing together now and the soonest I can get a new part is a week - not Amazon Prime capable, no one has it locally. I'm wondering if backflow protection is needed. I could get the plug out with some work. This is a completely closed system. I refill the pond with a garden hose after cleaning. All I can imagine the backflow preventer doing is keeping the weight of the water off the pump when it's not on which is about half the day - on a timer. Hard to imagine that is really needed.

Pretty sure this is the part:

https://store.aquascapeinc.com/p/check-valve-assembly-3

Here is a photo of the existing part, worn but plently servicable just as an elbow:

 

[Diehard]

A "Backflow Preventer" sole job is to prevent drinking water from being contaminated due to backflow. You are referring to a check valve which is used to prevent backflow also but is not an approved device to serve the function of a backflow preventer. It has other reasons for it's prevention of backflow.
Commonly on the discharge of a pump to prevent reverse rotation of the pumps impeller,etc.

So not seeing or visualizing exactly what the arrangement is I can't comment further on the potential importance of that check valve.

It's not code dictated.

You mention, "...keeping the weight of the water off the pump". It not a flooded discharge I assume , so wouldn't the water just run back leaving the discharge pipe empty?
would that require thet the pump be primed in order for it to pump again. (Centrifugal pump?)

 

[cmac2012]

Thanks for the quick reply. I should have known of that distinction. I didn't really think this would be code dictated but I knew that backflow prevention was. FWIW, here's a crude drawing of the setup:

The pump is an Aquascape 91020, 5284 GPH. Strong and durable little sucker. When the pond is full, there can't be much weight of water between the control box and the lower check valve. It occurs to me that I should replace the upper check valve as it might also be deteriorating and it's doing most of the work. There is an approx 5 gallon basin with filters at the top, from which the water spills over into the main creek. I suspect that weight is all on the main check valve.

 

[frodo]

,,,,,,,,,

 

[frodo]

i think, but am not certain, the ck valve is to keep the pump primed

 

[Diehard]

It's a relatively small sump but I assume the pump doesn't cycle on and off being a, relatively speaking, closed system?
So the box with valves is just a distribution box for the 3 discharges, and each has its own check valve.

I really can't think of a reason for what would appear to be a redundant check valve.

How often do you have to add water, on average?

Does it have some type of overflow path for when it rains?

Just curious.

EDIT: Being in a sump I assume it has a float and is always submerged.

 

[Diehard]

i think, but am not certain, the ck valve is to keep the pump primed

This is true with centrifugal pumps but it's not necessarily the only reason.
For example, in the case of a sump pump, you don't want the water in the discharge line to come back into the sump every time it stops pumping. This would of course shorten the start/stop cycle times.

 

[cmac2012]

It's a relatively small sump but I assume the pump doesn't cycle on and off being a, relatively speaking, closed system?
So the box with valves is just a distribution box for the 3 discharges, and each has its own check valve.

I really can't think of a reason for what would appear to be a redundant check valve.

How often do you have to add water, on average?

Does it have some type of overflow path for when it rains?

Just curious.

EDIT: Being in a sump I assume it has a float and is always submerged.

No float, it will always have water above it. When power is on, it's pumping. Here's a pic of the pump:

The first one lasted 9 years.

I recall them telling me that they add water every few weeks. Funny, we had a rainy winter and I don't recall any mention of it overflowing. Maybe there's an escape port I don't know of.

They installed this a few years before I met them, I wish I had a drawing of how the underground plumbing works. But as I piece it together, I'm sure the larger check valve at the box is for the main, central creek only. It has the basin at that top. The two creeks on either side are dependant on the check valve just above the pump. They each have a ball valve in the box, whereas the main creek has a large gate valve. They like to have good flow in the creek by the sidewalk. Takes a little finessing but if I limit flow to the main creek I can then send maybe 40% of the water to creek they want, 40% to the main, 20% to the far creek.

I should have it running tommorrow, I'll take pics.

 

[cmac2012]

Got it running in fine form. The owner has some technical training, he likes to weigh in with opinions and often his ideas are sound. We found that there are check-valves on all three lines going up to feed the creeks.

In the first view can see all three - the gate valve on the 3" line allows limiting the pressure that goes to the main overflow sump at the top of the main creek, this so the two smaller lines can see some of the water. In the second pic you can see the bulbous check valves for the two small lines under the box, something I wasn't aware of at first:

Here is what I'm calling the main overflow sump at the top:

I put a sharpie in the bottom so size could be gauged. I'm guessing 15 to 20 gallons. The two smaller creeks have no such resorvoir, just some rocks surrounded the place where the 1-1/2" PVC comes out. Might be one inch, didn't look that close.

A checkvalve is needed to hold that back, would be a lot of weight on the pump.

The owner said the same builders over-engineered the hell out of another project that eventually went south. He suggested we just cut out the plastic plug that had broken free inside the elbow shown in the first post and give it a go.

I managed to grip it with some of those long skinny visegrips and cut a third of it off with my Fein saw and out it came. Almost seems that the flow is stronger than ever and this pump is 3 to 4 years old. I don't think the small amount of back pressure from the height the three check valves about the waters surface is making the pumps vanes turn backward. I started and stopped it several times observing closely.

Here are pics of the main collection sump:

You can see two of the three stainless bolts I epoxied into holes I drilled in the opening. Those to support this stainless steel grating:

The original was a squarish piece of plastic stock for supporting a filter and gravel. It was breaking years ago, we tried a couple of solutions before I hit upon putting the filter inside the cavity thusly:

Two different filter materials FWIW.

Here's a Youtube of it in operation. At one point I turned the camera around and aimed it under a bush so you can see the rectangular shaped piece of flat rock covering the plastic box that contains the three valves.

They want the creek by the sidewalk to run strong, people walk next to it.